Sporulation and Dispersal of the Biological Control Agent Aspergillus flavus AF36 Under Field Conditions

Aflatoxins are carcinogens produced by the fungi Aspergillus flavus and A. parasiticus that contaminate pistachio crops. International markets reject pistachio when aflatoxins exceed permitted maximum levels. Releasing the atoxigenic strain AF36 of A. flavus is the leading aflatoxin pre-harvest control method. The product AF36 Prevail, sorghum grains coated with AF36 propagules, has been used in California since 2017. However, a high percentage of grains of the Prevail fail to sporulate in orchards. Here, the effect of soil moisture on the percentage of AF36 product grains sporulating (SG) and the quantity of spores per grain using a sporulation index (SI) was determined. Under controlled conditions, SG was higher than 85% when soil moisture was 13% or more, and SI increased with increasing soil moisture from 8.4 to 21%. The highest AF36 sporulation occurred near the micro-sprinklers when the grains were not impacted by the irrigation water drops. Arthropod predation was responsible for lost product grains, which was more pronounced in non-tilled soil than in tilled soil. Dispersal of the AF36 spores decreased markedly with the height and distance from the inoculum source, following a pattern of diffusion equations. However, AF36 spores easily reached canopies of pistachios located 10 m from the inoculum source. Our results indicate that AF36 Prevail should be applied close to the irrigation line in the moist soil area but avoiding the areas where excess irrigation causes water accumulation. The biocontrol of aflatoxins in California's pistachio production areas was optimized by improving the field realization of the biological control agent.

The dynamic changes in olive fruit phenolic metabolism and its contribution to the activation of quiescent Colletotrichum infection

Anthracnose, the most critical disease affecting olive fruits, is caused by Colletotrichum species. While developing olive fruits are immune to the pathogen regardless of the cultivar, the resistance level varies once the fruit ripens. The defense mechanisms responsible for this difference in resistance are not well understood. To explore this, we analyzed the phenolic metabolic pathways occurring in olive fruits and their susceptibility to the pathogen during ripening in two resistant cultivars ('Empeltre' and 'Frantoio') and two susceptible cultivars ('Hojiblanca' and 'Picudo'). Overall, resistant cultivars induced the synthesis of aldehydic and demethylated forms of phenols, which highly inhibited fungal spore germination. In contrast, susceptible cultivars promoted the synthesis of hydroxytyrosol 4-O-glucoside during ripening, a compound with no antifungal effect. This study showed that the distinct phenolic profiles between resistant and susceptible cultivars play a key role in determining olive fruit resistance to Colletotrichum species.

Pollen production in olive cultivars and its interannual variability

BACKGROUND AND AIMS

Olive (Olea europaea subsp. europaea var. europaea) is the most extensively cultivated fruit crop worldwide. It is considered a wind-pollinated and strictly outcrossing crop. Thus, elevated pollen production is crucial to guarantee optimum fruit set and yield. Despite these facts, the variability of pollen production within the cultivated olive has been scarcely studied. This study aimed to characterize this feature by analysing a representative set of worldwide olive cultivars.

METHODS

We evaluated the average number of pollen grains per anther in 57 principal cultivars over three consecutive years. We applied a standard generalized linear model (GLM) approach to study the influence of cultivar, year and the previous year's fruit load on the amount of pollen per anther. Additionally, the K-means method was used for cluster analysis to group cultivars based on their pollen production capacity.

KEY RESULTS

Pollen production per anther was highly variable among olive cultivars. The cultivar significantly accounted for 51.3 % of the variance in pollen production and the year for 0.3 %. The interaction between the two factors explained 8.4 % of the variance, indicating that not all cultivars were equally stable in producing pollen across the years. The previous year's fruit load and its interaction with the year were significant, but barely accounted for 1.5 % of the variance. Olive cultivars were classified into four clusters according to their capacity to produce pollen. Interestingly, the fourth cluster was composed of male-sterile cultivars, which presumably share this character by inheritance.

CONCLUSIONS

Pollen production per anther varied extensively within the cultivated olive. This variation was mainly driven by the cultivar and its interaction with the year. The differential capacity of olive cultivars to produce pollen should be considered not only for designing new orchards but also gardens where this species is used as an ornamental.

Pistachio Male Inflorescences as an Alternative Substrate for the Application of Atoxigenic Strains of Aspergillus flavus

Aflatoxins are carcinogens mainly produced by Aspergillus flavus and A. parasiticus in susceptible crops, including pistachio. The primary inoculum sources of these pathogens are plant debris in the orchard soils. In Californian fields, one approach to controlling aflatoxin contamination is based on releasing the atoxigenic strain of A. flavus AF36 in inoculated (coated) sorghum grains (AF36 Prevail). However, this control method can fail due to poor sporulation of the AF36 strain or sorghum grain losses due to predation. In 2008 and 2018, we showed that toxigenic and atoxigenic isolates of Aspergillus spp. frequently colonized fallen inflorescences of male pistachio trees. Under controlled conditions, strain AF36 profusely colonized pistachio male inflorescences when humidity was higher than 90%. However, there were significant differences between types of inflorescence (aerial > fallen). In 2016, we considerably (P = 0.015) increased the population of AF36 on the canopies of trees when fallen inflorescences were inoculated with AF36, compared with untreated trees. In 2017 and 2018, these differences were not detected (P > 0.05) due to cross-contamination of strain AF36 between seasons and neighboring plots. In any case, the density of AF36 spores on the canopy of the inflorescence-treated trees was similar (P > 0.05) to that on trees treated with the commercial product. Here, we present a new method for applying strain AF36 based on using a natural, abundant, and uniformly distributed substrate in pistachio fields, and we discuss how it can be improved. Furthermore, our results indicate that, in pistachio orchards where biocontrol practices are not conducted, eliminating this important source of toxigenic Aspergillus inoculum is recommended.

Study of the competition between Colletotrichum godetiae and C. nymphaeae, two pathogenic species in olive

Olive anthracnose, a critical olive fruit disease that adversely impacts oil quality, is caused by Colletotrichum species. A dominant Colletotrichum species and several secondary species have been identified in each olive-growing region. This study surveys the interspecific competition between C. godetiae, dominant in Spain, and C. nymphaeae, prevalent in Portugal, to shed light on the cause of this disparity. When Petri-dishes of Potato Dextrose Agar (PDA) and diluted PDA were co-inoculated with spore mixes produced by both species, C. godetiae displaced C. nymphaeae, even if the percentage of spores in the initial spore mix inoculation was just 5 and 95%, respectively. The C. godetiae and C. nymphaeae species showed similar fruit virulence in separate inoculations in both cultivars, the Portuguese cv. Galega Vulgar and the Spanish cv. Hojiblanca, and no cultivar specialization was observed. However, when olive fruits were co-inoculated, the C. godetiae species showed a higher competitive ability and partially displaced the C. nymphaeae species. Furthermore, both Colletotrichum species showed a similar leaf survival rate. Lastly, C. godetiae was more resistant to metallic copper than C. nymphaeae. The work developed here allows a deeper understanding of the competition between C. godetiae and C. nymphaeae, which could lead to developing strategies for more efficient disease risk assessment.

Resistance to Aspergillus flavus and Aspergillus parasiticus in Almond Advanced Selections and Cultivars and Its Interaction with the Aflatoxin Biocontrol Strategy

Aflatoxin contamination of almond kernels, caused by Aspergillus flavus and A. parasiticus, is a severe concern for growers because of its high toxicity. In California, the global leader of almond production, aflatoxin can be managed by applying the biological control strain AF36 of A. flavus and selecting resistant cultivars. Here, we classified the almond genotypes by K-Means cluster analysis into three groups (susceptible [S], moderately susceptible [MS], or resistant [R]) based on aflatoxin content of inoculated kernels. The protective effects of the shell and seedcoat in preventing aflatoxin contamination were also examined. The presence of intact shells reduced aflatoxin contamination >100-fold_. The seedcoat provided a layer of protection but not complete protection. In kernel inoculation assays, none of the studied almond genotypes showed a total resistance to the pathogen. However, nine traditional cultivars and four advanced selections were classified as R. Because these advanced selections contained germplasm derived from peach, we compared the kernel resistance of three peach cultivars to that shown by kernels of an R (Sonora) and an S (Carmel) almond cultivar and five pistachio cultivars. Overall, peach kernels were significantly more resistant to the pathogen than almond kernels, which were more resistant than pistachio kernels. Finally, we studied the combined effect of the cultivar resistance and the biocontrol strain AF36 in limiting aflatoxin contamination. For this, we coinoculated almond kernels of R Sonora and S Carmel with AF36 72 h before or 48 h after inoculating with an aflatoxin-producing strain of A. flavus. The percentage of aflatoxin reduction by AF36 strain was greater in kernels of Carmel (98%) than in those of Sonora (83%). Cultivar resistance also affected the kernel colonization by the biological control strain. AF36 strain limited aflatoxin contamination in almond kernels even when applied 48 h after the aflatoxin-producing strain. Our results show that biocontrol combined with the use of cultivars with resistance to aflatoxin contamination can result in a more robust protection strategy than the use of either practice in isolation.

Diversity of Colletotrichum Species Associated with Olive Anthracnose Worldwide

Olive anthracnose caused by Colletotrichum species causes dramatic losses of fruit yield and oil quality worldwide. A total of 185 Colletotrichum isolates obtained from olives and other hosts showing anthracnose symptoms in Spain and other olive-growing countries over the world were characterized. Colony and conidial morphology, benomyl-sensitive, and casein-hydrolysis activity were recorded. Multilocus alignments of ITS, TUB2, ACT, CHS-1, HIS3, and/or GAPDH were conducted for their molecular identification. The pathogenicity of the most representative Colletotrichum species was tested to olive fruits and to other hosts, such as almonds, apples, oleander, sweet oranges, and strawberries. In general, the phenotypic characters recorded were not useful to identify all species, although they allowed the separation of some species or species complexes. ITS and TUB2 were enough to infer Colletotrichum species within C. acutatum and C. boninense complexes, whereas ITS, TUB2, ACT, CHS-1, HIS-3, and GADPH regions were necessary to discriminate within the C. gloesporioides complex. Twelve Colletotrichum species belonging to C. acutatum, C. boninense, and C. gloeosporioides complexes were identified, with C. godetiae being dominant in Spain, Italy, Greece, and Tunisia, C. nymphaeae in Portugal, and C. fioriniae in California. The highest diversity with eight Colletotrichum spp. was found in Australia. Significant differences in virulence to olives were observed between isolates depending on the Colletotrichum species and host origin. When other hosts were inoculated, most of the Colletotrichum isolates tested were pathogenic in all the hosts evaluated, except for C. siamense to apple and sweet orange fruits, and C. godetiae to oleander leaves.

Cultivar Susceptibility to Natural Infections Caused by Fungal Grapevine Trunk Pathogens in La Mancha Designation of Origin (Spain)

Grapevine trunk diseases (GTDs) are one of the main biotic stress factors affecting this crop. The use of tolerant grapevine cultivars would be an interesting and sustainable alternative strategy to control GTDs. To date, most studies about cultivar susceptibility have been conducted under controlled conditions, and little information is available about tolerance to natural infections caused by GTD fungi. The objectives of this study were: (i) to identify tolerant cultivars to GTD fungi within a Spanish germplasm collection, based on external symptoms observed in the vineyard; and (ii) to characterize the pathogenic mycoflora associated with symptomatic vines. For this purpose, a grapevine germplasm collection including 22 white and 25 red cultivars was monitored along three growing seasons, and their susceptibility for esca foliar symptoms was assessed. Fungi were identified by using morphological and molecular methods. Cultivars such as, 'Monastrell', 'Graciano', 'Cabernet Franc', 'Cabernet Sauvignon', 'Syrah', 'Moscatel de Alejandría', 'Sauvignon Blanc', and 'Airén' displayed high susceptibility to GTDs, whereas others such as 'Petit Verdot', 'Pinot Noir', 'Chardonnay', and 'Riesling' were considered as tolerant. The prevalent fungal species isolated from symptomatic vines were Phaeomoniella chlamydospora (27.9% of the fungal isolates), Cryptovalsa ampelina (24.6%), and Dothiorella sarmentorum (21.3%).

Quantification of the Aflatoxin Biocontrol Strain Aspergillus flavus AF36 in Soil and in Nuts and Leaves of Pistachio by Real-Time PCR

The species Aspergillus flavus and A. parasiticus are commonly found in the soils of nut-growing areas in California. Several isolates can produce aflatoxins that occasionally contaminate nut kernels, conditioning their sale. Strain AF36 of A. flavus, which does not produce aflatoxins, is registered as a biocontrol agent for use in almond, pistachio, and fig crops in California. After application in orchards, AF36 displaces aflatoxin-producing Aspergillus spp. and thus reduces aflatoxin contamination. Vegetative compatibility assays (VCAs) have traditionally been used to track AF36 in soils and crops where it has been applied. However, VCAs are labor intensive and time consuming. Here, we developed a quantitative real-time PCR (qPCR) protocol to quantify proportions of AF36 accurately and efficiently in different substrates. Specific primers to target AF36 and toxigenic strains of A. flavus and A. parasiticus were designed based on the sequence of aflC, a gene essential for aflatoxin biosynthesis. Standard curves were generated to calculate proportions of AF36 based on threshold cycle values. Verification assays using pure DNA and conidial suspension mixtures demonstrated a significant relationship by regression analysis between known and qPCR-measured AF36 proportions in DNA (R² = 0.974; P < 0.001) and conidia mixtures (R² = 0.950; P < 0.001). Tests conducted by qPCR in pistachio leaves, nuts, and soil samples demonstrated the usefulness of the qPCR method to precisely quantify proportions of AF36 in diverse substrates, ensuring important time and cost savings. The outputs of this study will serve to design better aflatoxin management strategies for pistachio and other crops.

Influence of genetic and interannual factors on the phenolic profiles of virgin olive oils

Phenolic compounds in virgin olive oil (VOO) contribute to its health properties, organoleptic features and oxidative stability. In this study, a total of 44 olive tree cultivars categorized by the International Olive Council to be among the most internationally widespread varieties were exhaustively and homogenously evaluated by analysis of the VOO phenolic profile during three consecutive crop seasons. Differences among cultivars resulted in up to 15-fold variations in the total phenol concentration. The 'cultivar' factor contributed the most to the variance (66.8% for total phenolic concentration) for almost all the phenols. However, the 'interannual variability' factor and the interaction 'cultivar x interannual variability' exhibited significant influences on specific phenols. According to the phenolic profile of the VOOs, we determined the presence of three groups of cultivars marked by the predominance of secoiridoid derivatives, which supports the phenolic profile as a criterion to be considered in olive breeding programs.

The phenolic profile of virgin olive oil is influenced by malaxation conditions and determines the oxidative stability

Phenolic compounds largely contribute to the nutraceutical properties of virgin olive oil (VOO), the organoleptic attributes and the shelf life due to their antioxidant capabilities. Due to the relevance of malaxation in the oil extraction process, we tested the effects of malaxation time on the concentrations of relevant phenolic compounds in VOO, and we evaluated the influence of performing malaxation under vacuum. An increase in malaxation time significantly decreased the concentrations of aglycone isomers of oleuropein and ligstroside but, conversely, increased the oleocanthal and oleacein contents. Additionally, malaxation under vacuum led to an increase in phenolic contents compared to standard conditions carried out at atmospheric pressure. Finally, we explored the possibility of predicting the VOO oxidative stability on the basis of the phenolic profile, and a model (R² = 0.923; p < 0.0001) was obtained by combining the concentration of the VOO phenolic compounds and the main fatty acids.

Effect of Cultivar Resistance and Soil Management on Spatial-Temporal Development of Verticillium Wilt of Olive: A Long-Term Study

Verticillium wilt, caused by Verticillium dahliae, challenges olive cultivation and an Integrated Disease Management (IDM) approach is the best-suited tool to combat it. Since 1998, an IDM strategy in an orchard (called Granon, Spain) of the susceptible cv. Picual was conducted by increasing planting density with moderately resistant cv. Frantoio, chemical weed control, and replanting of dead olives with cv. Frantoio following soil solarization. The Verticillium wilt epidemic in Granon orchard was compared to the epidemic in a non-IDM orchard (called Ancla, Spain) with plowed soil and dead Picual olives replanted with the same cultivar. Field evaluations (2012-2013) showed an incidence and severity of the disease as Picual-Ancla > Picual-Granon > Frantoio-Granon. The spatiotemporal dynamics of the Verticillium epidemics from 1998 to 2010 were monitored with digital images using SIG. The annual tree mortalities were 5.6% for Picual olives in Ancla orchard, and 3.1 and 0.7% for Picual and Frantoio olives in Granon orchard, respectively. There was a negative relationship between the mortality of olive trees (%) by the pathogen and the height (m) above sea level. The annual mortality of cv. Picual olives was positively correlated with spring rainfalls. The Index of Dispersion and beta-binomial distribution showed aggregation of Verticillium-dead olives. In conclusion, this IDM strategy considerably reduced the disease in comparison with traditional agronomic practices.

Identification and Characterization of Neofabraea kienholzii and Phlyctema vagabunda Causing Leaf and Shoot Lesions of Olive in California

California produces over 95% of the olives grown in the United States. In 2017, California's total bearing acreage for olives was 14,570 hectares producing 192,000 tons of olives valued at $186.6 million. During the early spring of 2016, unusual leaf and shoot lesions were detected in olive trees from superhigh-density orchards in the Northern San Joaquin and Sacramento valleys of California. Affected trees displayed numerous leaf and shoot lesions developing at wounds created by mechanical harvesters. The 'Arbosana' cultivar was highly affected by the disease, whereas the disease was sporadic in 'Arbequina' and not found in 'Koroneiki' cultivar. Two fungal species, Neofabraea kienholzii and Phlyctema vagabunda, were found to be consistently associated with the disease, and Koch's postulates were completed. Species identity was confirmed by morphology and molecular data of the partial large subunit rDNA, the internal transcribed spacer region, and partial beta-tubulin region. The disease signs and symptoms are described and illustrated.

Ecology and Epidemiology of Diseases of Nut Crops and Olives Caused by Botryosphaeriaceae Fungi in California and Spain

In recent decades, the cultivated area and production of nuts and olives have increased, driven by an increasing consumer interest in healthier food. Diseases of almond, pistachio, olive, and walnut crops caused by species belonging to the Botryosphaeriaceae family have caused concern worldwide. Although considerable progress has been made in elucidating the etiology of these diseases, scientific knowledge of other aspects of these diseases is more limited. In this article, we present an overview of the most important diseases caused by Botryosphaeriaceae fungi affecting almond, pistachio, olive, and walnut crops by focusing on ecology and epidemiology, primarily in California and Spain.

Interaction Between Diaporthe rhusicola and Neofusicoccum mediterraneum Causing Branch Dieback and Fruit Blight of English Walnut in California, and the Effect of Pruning Wounds on the Infection

Botryosphaeriaceae and Diaporthaceae species are the causal agents of branch dieback of English walnut in California. In this study, the effects of the interaction between Neofusicoccum mediterraneum and Diaporthe rhusicola were evaluated in vitro by using mycelial plugs or spore suspensions and in vivo by inoculating shoots and epicarps (hulls) of walnut. Single inoculations of each species and different coinfection treatments were performed under laboratory or field conditions. The influence of shoot age and susceptibility of bark or pith tissues to N. mediterraneum and D. rhusicola infection after pruning was also evaluated. In in vitro experiments, spore germination of D. rhusicola was significantly (P < 0.0001) reduced in the presence of N. mediterraneum spores. When D. rhusicola was inoculated at 4 days before N. mediterraneum, a delay in lesion development in shoots and hulls was observed compared with the other two interaction treatments. One- to 2-year-old shoots were more susceptible to infection and colonization by N. mediterraneum than 3- to 4-year-old shoots. In young shoots, inoculation in the pith tissue resulted in longer lesions than those observed on shoots inoculated in the bark. No significant differences were observed between the development of internal or external necrosis and the age of the shoots, or the susceptibility of bark and pith to D. rhusicola infection. This information is essential to better understanding the complex situation of this walnut disease toward developing control management strategies.

Atoxigenic Aspergillus flavus Isolates Endemic to Almond, Fig, and Pistachio Orchards in California with Potential to Reduce Aflatoxin Contamination in these Crops

In California, aflatoxin contamination of almond, fig, and pistachio has become a serious problem in recent years due to long periods of drought and probably other climatic changes. The atoxigenic biocontrol product Aspergillus flavus AF36 has been registered for use to limit aflatoxin contamination of pistachio since 2012 and for use in almond and fig since 2017. New biocontrol technologies employ multiple atoxigenic genotypes because those provide greater benefits than using a single genotype. Almond, fig, and pistachio industries would benefit from a multi-strain biocontrol technology for use in these three crops. Several A. flavus vegetative compatibility groups (VCGs) associated with almond, fig, and pistachio composed exclusively of atoxigenic isolates, including the VCG to which AF36 belongs to, YV36, were previously characterized in California. Here, we report additional VCGs associated with either two or all three crops. Representative isolates of 12 atoxigenic VCGs significantly (P < 0.001) reduced (>80%) aflatoxin accumulation in almond and pistachio when challenged with highly toxigenic isolates of A. flavus and A. parasiticus under laboratory conditions. Isolates of the evaluated VCGs, including AF36, constitute valuable endemic, well-adapted, and efficient germplasm to design a multi-crop, multi-strain biocontrol strategy for use in tree crops in California. Availability of such a strategy would favor long-term atoxigenic A. flavus communities across the affected areas of California, and this would result in securing domestic and export markets for the nut crop and fig farmer industries and, most importantly, health benefits to consumers.

Characterization of Argentinian Endemic Aspergillus flavus Isolates and Their Potential Use as Biocontrol Agents for Mycotoxins in Maize

Maize (Zea mays L.) is a highly valuable crop in Argentina, frequently contaminated with the mycotoxins produced by Aspergillus flavus. Biocontrol products formulated with atoxigenic (nontoxic) strains of this fungal species are well known as an effective method to reduce this contamination. In the present study, 83 A. flavus isolates from two maize regions of Argentina were characterized and evaluated for their ability to produce or lack of producing mycotoxins in order to select atoxigenic strains to be used as potential biocontrol agents (BCA). All of the isolates were tested for aflatoxin and cyclopiazonic acid (CPA) production in maize kernels and a liquid culture medium. Genetic diversity of the nonaflatoxigenic isolates was evaluated by analysis of vegetative compatibility groups (VCG) and confirmation of deletions in the aflatoxin biosynthesis cluster. Eight atoxigenic isolates were compared for their ability to reduce aflatoxin and CPA contamination in maize kernels in coinoculation tests. The A. flavus population was composed of 32% aflatoxin and CPA producers and 52% CPA producers, and 16% was determined as atoxigenic. All of the aflatoxin producer isolates also produced CPA. Aflatoxin and CPA production was significantly higher in maize kernels than in liquid medium. The 57 nonaflatoxigenic strains formed six VCG, with AM1 and AM5 being the dominant groups, with a frequency of 58 and 35%, respectively. In coinoculation experiments, all of the atoxigenic strains reduced aflatoxin from 54 to 83% and CPA from 60 to 97%. Members of group AM1 showed a greater aflatoxin reduction than members of AM5 (72 versus 66%) but no differences were detected in CPA production. Here, we described for the first time atoxigenic isolates of A. flavus that show promise to be used as BCA in maize crops in Argentina. This innovating biological control approach should be considered, developed further, and used by the maize industry to preserve the quality properties and food safety of maize kernels in Argentina.

Fungal communities associated with almond throughout crop development: Implications for aflatoxin biocontrol management in California

Interactions between pathogenic and nonpathogenic fungal species in the tree canopy are complex and can determine if disease will manifest in the plant and in other organisms such as honey bees. Seasonal dynamics of fungi were studied in an almond orchard in California where experimental release of the atoxigenic biopesticide Aspergillus flavus AF36 to displace toxigenic Aspergillus strains has been conducted for five years. The presence of the vegetative compatibility group (VCG) YV36, to which AF36 belongs, in the blossoms, and the honey bees that attend these blossoms, was assessed. In blossoms, A. flavus frequencies ranged from 0 to 4.5%, depending on the year of study. Frequencies of honey bees carrying A. flavus ranged from 6.5 to 10%. Only one A. flavus isolate recovered from a blossom in 2016 belonged to YV36, while members of the VCG were not detected contaminating honey bees. Exposure of pollinator honey bees to AF36 was detected to be very low. The density of several Aspergillus species was found to increase during almond hull split and throughout the final stages of maturation; this also occurred in pistachio orchards during the maturation period. Additionally, we found that AF36 effectively limited almond aflatoxin contamination in laboratory assays. This study provides knowledge and understanding of the seasonal dynamics of Aspergillus fungi and will help design aflatoxin management strategies for almond. The evidence of the low levels of VCG YV36 encountered on almond blossoms and bees during pollination and AF36's effectiveness in limiting aflatoxin contamination in almond provided additional support for the registration of AF36 with USEPA to use in almond in California.

Cultivar influence on variability in olive oil phenolic profiles determined through an extensive germplasm survey

Despite the evident influence of the cultivar on olive oil composition, few studies have been devoted to exploring the variability of phenols in a representative number of monovarietal olive oils. In this study, oil samples from 80 cultivars selected for their impact on worldwide oil production were analyzed to compare their phenolic composition by using a method based on LC-MS/MS. Secoiridoid derivatives were the most concentrated phenols in virgin olive oil, showing high variability that was significantly due to the cultivar. Multivariate analysis allowed discrimination between four groups of cultivars through their phenolic profiles: (i) richer in aglycon isomers of oleuropein and ligstroside; (ii) richer in oleocanthal and oleacein; (iii) richer in flavonoids; and (iv) oils with balanced but reduced phenolic concentrations. Additionally, correlation analysis showed no linkage among aglycon isomers and oleocanthal/oleacein, which can be explained by the enzymatic pathways involved in the metabolism of both oleuropein and ligstroside.

Detection of latent infections caused by Colletotrichum sp. in olive fruit

AIMS

To set up a practical method to detect latent infections of Colletotrichum sp., the causal agent of olive anthracnose, on olives before the onset of disease symptoms.

METHODS AND RESULTS

Freezing, sodium hydroxide (NaOH), ethanol and ethylene treatments were evaluated to detect latent infections on inoculated and naturally infected olive fruit by Colletotrichum sp. as non-hazardous alternatives to paraquat. Treatments were conducted using fruit of cultivars Arbequina and Hojiblanca. The disease incidence and T₅₀ were calculated. Dipping in NaOH 0·05% solution and the paraquat method were the most effective treatments on both inoculated and naturally infected fruit, although the value of T₅₀ was lower for the NaOH method than for the paraquat method in one of the experiments. Subsequently, the dipping time in NaOH 0·05% was evaluated. Longer dipping times in NaOH 0·05% were better than shorter ones in cultivar Arbequina, with 72 h being the most effective in cultivar Hojiblanca.

CONCLUSIONS

NaOH solution is a practical method to detect latent infections of Colletotrichum sp. on immature olive fruit.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is relevant because we set up a viable, non-hazardous alternative to paraquat to detect latent infections of Colletotrichum sp. using NaOH. The use of NaOH is a simple and eco-friendly tool that allows the determination of the level of latent infections by Colletotrichum in olives. Therefore, our method will be useful in decision-making processes for disease management before the appearance of the first visible symptoms.

Effects of Wound Size, Amount of Sap, and Number of Blighted Nuts on Infection of Pistachio Organs by Neofusicoccum mediterraneum

Laboratory and field studies were conducted to determine the effects of wounding of nut exocarp, susceptibility period after wounding, and sap nut on infection of pistachio nut by Neofusicoccum mediterraneum, the main causal agent of panicle and shoot blight of pistachio. Under controlled conditions and in the field, detached nuts were inoculated with a conidial suspension 30 min before or after wounding. In addition, a 30-µl drop of pistachio sap was placed on the surface of noninjured nuts 30 min before or after they were wounded and then inoculated. Wounding increased the disease severity under both controlled and field conditions. The addition of sap increased the susceptibility of nuts under controlled conditions but not in the field, possibly due to dried sap blocking the pathogen infection. When nuts of Kerman, Kalehghouchi, and Golden Hills pistachio were wounded and inoculated at different time periods after wounding; the nuts of the three cultivars were highly susceptible to pathogen infection during at least the first 24 h after wounding. Under field conditions, there was not a clear effect of increasing the number of inoculated nuts per panicle or the inoculation position (basal or apical) in killing (blight) of the panicle. Conversely, inoculations conducted with mycelial plugs resulted in higher disease, increased the proportion of dead panicles, and resulted in faster symptom expression than inoculations conducted with a conidial suspension. To determine the temporal infection pattern, leaves and panicles were regularly collected from different orchards from 2004 to 2007 and the pathogen was isolated on medium. Important differences in latent infection were detected between years and orchards, with nut and rachis being, in general, the tissues most susceptible to infection. Results of this study help in better understanding the dynamic of infection and colonization of pistachio by N. mediterraneum.

Variability in Susceptibility to Anthracnose in the World Collection of Olive Cultivars of Cordoba (Spain)

Anthracnose of olive (Olea europaea ssp. europaea L.), caused by Colletotrichum species, is a serious disease causing fruit rot and branch dieback, whose epidemics are highly dependent on cultivar susceptibility and environmental conditions. Over a period of 10 years, there have been three severe epidemics in Andalusia (southern Spain) that allowed us to complete the assessment of the World Olive Germplasm Bank of Córdoba, one of the most important cultivar collections worldwide.A total of 308 cultivars from 21 countries were evaluated, mainly Spain (174 cvs.), Syria (29 cvs.), Italy (20 cvs.), Turkey (15 cvs.), and Greece (16 cvs.). Disease assessments were performed using a 0-10 rating scale, specifically developed to estimate the incidence of symptomatic fruit in the tree canopy. Also, the susceptibility of five reference cultivars was confirmed by artificial inoculation. Because of the direct relationship between the maturity of the fruit and their susceptibility to the pathogen, evaluations were performed at the end of fruit ripening, which forced coupling assessments according to the maturity state of the trees. By applying the cluster analysis to the 308 cultivars, these were classified as follows: 66 cvs. highly susceptible (21.4%), 83 cvs. susceptible (26.9%), 66 cvs. moderately susceptible (21.4%), 61 cvs. resistant (19.8%), and 32 cvs. highly resistant (10.4%). Representative cultivars of these five categories are "Ocal," "Lechín de Sevilla," "Arbequina," "Picual," and "Frantoio," respectively. With some exceptions, such as cvs. Arbosana, Empeltre and Picual, most of the Spanish cultivars, such as "Arbequina," "Cornicabra," "Hojiblanca," "Manzanilla de Sevilla," "Morisca," "Picudo," "Farga," and "Verdial de Huévar" are included in the categories of moderately susceptible, susceptible or highly susceptible. The phenotypic evaluation of anthracnose reaction is a limiting factor for the selection of olive cultivars by farmers, technicians, and breeders.

Cytoskeleton reorganization/disorganization is a key feature of induced inaccessibility for defence to successive pathogen attacks

In this work, we investigated the involvement of the long-term dynamics of cytoskeletal reorganization on the induced inaccessibility phenomenon by which cells that successfully defend against a previous fungal attack become highly resistant to subsequent attacks. This was performed on pea through double inoculation experiments using inappropriate (Blumeria graminis f. sp. avenae, Bga) and appropriate (Erysiphe pisi, Ep) powdery mildew fungi. Pea leaves previously inoculated with Bga showed a significant reduction of later Ep infection relative to leaves inoculated only with Ep, indicating that cells had developed induced inaccessibility. This reduction in Ep infection was higher when the time interval between Bga and Ep inoculation ranged between 18 and 24 h, although increased penetration resistance in co-infected cells was observed even with time intervals of 24 days between inoculations. Interestingly, this increase in resistance to Ep following successful defence to the inappropriate Bga was associated with an increase in actin microfilament density that reached a maximum at 18-24 h after Bga inoculation and very slowly decreased afterwards. The putative role of cytoskeleton reorganization/disorganization leading to inaccessibility is supported by the suppression of the induced resistance mediated by specific actin (cytochalasin D, latrunculin B) or general protein (cycloheximide) inhibitors.

Identification of Fungal Species Associated with Branch Dieback of Olive and Resistance of Table Cultivars to Neofusicoccum mediterraneum and Botryosphaeria dothidea

Over two consecutive seasons, 16 olive orchards with trees exhibiting dieback symptoms on branches were surveyed in southern Spain. The six dominant fungal species recovered were characterized by means of phenotypic observations, DNA analysis (by sequencing of the internal transcribed spacer, β-tubulin, and large subunit nuclear ribosomal DNA regions), and pathogenicity tests. Additionally, three isolates collected from Tunisian olive trees showing similar dieback symptoms, one isolate of Colletotrichum godetiae, and a reference isolates of Neofusicoccum mediterraneum were included. The resistance of the 11 most important table cultivars to N. mediterraneum and Botryosphaeria dothidea, the causal agent of "escudete" (small shield) of fruit, was studied by the inoculation of branches and immature fruit, respectively. The species Cytospora pruinosa, N. mediterraneum, Nothophoma quercina, Comoclathris incompta, and Diaporthe sp. were identified. Only N. mediterraneum and C. incompta were able to induce the typical dieback symptoms and cankers that affected the development of the plants. The species N. mediterraneum was the most virulent among the evaluated species, although differences in virulence among its isolates were observed. The remaining fungal species were weakly pathogenic to nonpathogenic on plants. According to resistance tests, 'Gordal Sevillana' and 'Manzanilla Cacereña' were the most susceptible to branch dieback caused by N. mediterraneum. Furthermore, the fruit of 'Aloreña de Atarfe' and 'Manzanilla de Sevilla' were the most susceptible to B. dothidea. Knowledge of the etiology and cultivar resistance of these diseases will help to establish better control measures.

The Effect of Short Irrigation Frequencies on the Development of Verticillium Wilt in the Susceptible Olive Cultivar 'Picual' under Field Conditions

The effect of irrigation frequency (daily [T1], biweekly [T2], and dryland [T3]) on Verticillium wilt of olive was studied in two fields that were naturally infested with Verticillium dahliae in southern Spain and planted to 'Picual' olive. Disease onset (average 61 weeks after planting) and disease incidence (average 75.6%) did not differ among irrigation treatments in both fields. Irrigation consistently increased disease development regarding dryland treatment, but this effect varied over time. In experiment I, T1, the relative area under the disease progress curve was greater on all recording dates (ranging from 15.8 to 33.7) in comparison with T3 (average 6.6). Data for experiment II were similar to this on the most favorable dates for disease (March to April). The T2 treatment value varied over time depending on the season and experimental field, being difficult to differentiate from the values of T1 and T3. Significant correlation between disease incidence and severity increments during spring and fall with the soil water content of the same or previous favorable seasons was observed. Through these correlations, we detected soil water contents of 24.3% (experiment I) and 23.6% (experiment II), where the increments of disease parameters remained at zero. Therefore, scheduling irrigation treatments based on rainfall may be a feasible method for maintaining the soil moisture below levels that favor for disease development.

Cultivar and Tree Density As Key Factors in the Long-Term Performance of Super High-Density Olive Orchards

Super high-density (SHD) olive orchards are rapidly expanding since the first plantation was set up in Spain in the 1990s. Because there are no long-term studies characterizing these systems, it is unknown if densities above a certain threshold could trigger competition among fully-grown trees, compromising their development. Over 14 years we have evaluated the performance of the major olive cultivars currently planted in SHD systems ("Arbequina," Arbequina IRTA-i·18, "Arbosana," "Fs-17," and "Koroneiki") and nine SHD designs ranging from 780 to 2254 trees ha(-1) for the cultivar "Arbequina." Remarkably, the accumulated fruit and oil production of the five cultivars increased linearly over time. Our data indicated the favorable long-term performance of the evaluated cultivars with an average annual oil production of 2.3 t ha(-1). Only "Fs-17" did not perform well to the SHD system in our conditions and it yielded about half (1.2 t ha(-1)) of the other cultivars. In the density trial for "Arbequina," both fruit and oil accumulated production increased over time as a function of tree density. Thus, the accumulated oil yield ranged from 16.1 t ha(-1) for the lowest density (780 trees ha(-1)) to 29.9 t ha(-1) for the highest (2254 trees ha(-1)). In addition, we note that the accumulated production per surface unit showed a better correlation with the hedgerow length than the tree density. Thus, the current planting designs of SHD olive orchards can be further improved taking this parameter into account. Despite observations that some irregular patterns of crop distribution have arisen, our olive hedgerows are still fully productive after 14 years of planting. This result contradicts previous experiences that showed declines in production 7 or 8 years after planting due to high vigor, shading, and limited ventilation.

Characterization of a Colletotrichum population causing anthracnose disease on Olive in northern Tunisia

AIMS

To phenotypically, physiologically and molecularly characterize the causal agent of olive anthracnose in the northern Tunisia and to study its genetic variability and pathogenicity.

METHODS AND RESULTS

A total of 43 isolates were obtained from symptomatic olives collected from four regions in northern Tunisia. A range of morphological and physiological characteristics was recorded; and a phylogenetic study, based on the sequence analysis of both internal transcribed spacers and TUB2 gene regions, was performed. Of the 43 isolates, 41 were identified as Colletotrichum acutatum s.s, and only two were affiliated to Colletotrichum gloeosporioides s.s. Two more representative Spanish isolates, included for comparison, were identified as Colletotrichum godetiae. Using six inter-simple-sequence-repeat markers, homogeneity between isolates from different locations and within the same species was recorded. In pathogenicity and virulence studies, C. gloeosporioides s.s was found to be less virulent, while the Spanish C. godetiae isolate was significantly more virulent than the Tunisian C. acutatum s.s.

CONCLUSIONS

Olive anthracnose in the North of Tunisia is mainly caused by C. acutatum s.s species.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study of olive anthracnose in Tunisia, which combines both phenotypic and molecular approaches. Colletotrichum acutatum s.s group was recorded for the first time in the country as the causal agent of olive anthracnose.

How Does Host Carbon Concentration Modulate the Lifestyle of Postharvest Pathogens during Colonization?

Postharvest pathogens can penetrate fruit by breaching the cuticle or directly through wounds, and they show disease symptoms only long after infection. During ripening and senescence, the fruit undergo physiological processes accompanied by a decline in antifungal compounds, which allows the pathogen to activate a mechanism of secretion of small effector molecules that modulate host environmental pH. These result in the activation of genes under their optimal pH conditions, enabling the fungus to use a specific group of pathogenicity factors at each particular pH. New research suggests that carbon availability in the environment is a key factor triggering the production and secretion of small pH-modulating molecules: ammonia and organic acids. Ammonia is secreted under limited carbon and gluconic acid under excess carbon. This mini review describes our most recent knowledge of the mechanism of activation of pH-secreted molecules and their contribution to colonization by postharvest pathogens to facilitate the transition from quiescence to necrotrophic lifestyle.

Temperature and water stress during conditioning and incubation phase affecting Orobanche crenata seed germination and radicle growth

Orobanche crenata is a holoparasitic plant that is potentially devastating to crop yield of legume species. Soil temperature and humidity are known to affect seed germination, however, the extent of their influence on germination and radicle growth of those of O. crenata is largely unknown. In this work, we studied the effects of temperature, water potential (Ψt) and the type of water stress (matric or osmotic) on O. crenata seeds during conditioning and incubation periods. We found that seeds germinated between 5 and 30°C during both periods, with a maximum around 20°C. Germination increased with increasing Ψt from -1.2 to 0 MPa during conditioning and incubation periods. Likewise, seed germination increased logarithmically with length of conditioning period until 40 days. The impact of the type of water stress on seed germination was similar, although the radicle growth of seeds under osmotic stress was lower than under matric stress, what could explain the lowest infestation of Orobanche sp. in regions characterized by saline soil. The data in this study will be useful to forecast infection of host roots by O. crenata.

Relative Susceptibility of New Olive Cultivars to Spilocaea oleagina, Colletotrichum acutatum, and Pseudocercospora cladosporioides

The evaluation of the relative susceptibility of new cultivars to the main diseases of a crop is a key point to consider prior to their release to the nursery industry. This study provides a rigorous characterization of the resistance of 15 new olive cultivars and their genitors ('Arbequina,' 'Frantoio,' and 'Picual') to the three main aerial diseases, peacock spot, anthracnose, and cercosporiosis caused by Spilocaea oleagina, Colletotrichum acutatum, and Pseudocercospora cladosporioides, respectively. To do so, developing leaves and detached green-yellowish fruit were inoculated in laboratory tests with S. oleagina and C. acutatum, respectively, using conidial suspensions of both pathogens. Additionally, a previously validated rating scale was used to assess the incidence of leaves with symptoms of S. oleagina or P. cladosporioides and the fruit rot incidence of C. acutatum in the trees for four years under field conditions. As a result, only two of the cultivars were susceptible to peacock spot, most likely because these new cultivars were previously screened for resistance to the disease on previous phases of the breeding program. Conversely, the 15 cultivars were susceptible or moderately susceptible to cercosporiosis. Five of the 15 new cultivars were classified as resistant to anthracnose, with four of them descendants of 'Frantoio' × 'Picual' crosses. In addition, the cultivars resistance to C. acutatum showed a negative linear correlation with the total phenols content of olive oil. This information regarding disease reaction of the new olive cultivars is essential for nursery industry and growers.

Sensitivities of Baseline Isolates and Boscalid-Resistant Mutants of Alternaria alternata from Pistachio to Fluopyram, Penthiopyrad, and Fluxapyroxad

Resistance of Alternaria alternata to boscalid, the first succinate dehydrogenase inhibitor (SDHI) fungicide labeled on pistachio, has become a common occurrence in California pistachio orchards and affects the performance of this fungicide. In this study, we established the baseline sensitivities of A. alternata to the new SDHIs fluopyram, fluxapyroxad, and penthiopyrad and assessed their cross resistance patterns with boscalid. Examination of the effective fungicide concentration that inhibits mycelial growth to 50% relative to the control (EC₅₀) for 50 baseline isolates revealed that the majority were sensitive to boscalid, penthiopyrad, fluopyram, and fluxapyroxad. Analysis of EC₅₀ values for boscalid for 117 A. alternata isolates originating from boscalid-exposed orchards showed that 44, 3, 1, and 69 isolates had sensitive, reduced sensitivity, moderately resistant, and highly resistant boscalid phenotypes, respectively. Molecular investigation of the occurrence of known SDH mutations showed that, among the 69 isolates highly resistant to boscalid, 44, 2, 14, and 1 isolates possessed the mutations leading to the H277Y, H277R, H134R, and H133R amino acid substitutions in AaSDHB, AaSDHB, AaSDHC, and AaSDHD subunits, respectively. Some SDHB or SDHC mutants displayed highly sensitive, sensitive, or reduced sensitivity phenotypes toward penthiopyrad or fluxapyroxad, whereas other had low, moderate, or high levels of resistance to these fungicides. In contrast, all the SDHB mutants were sensitive to fluopyram, while 10, 5, and 1 SDHC mutants had sensitive, reduced sensitivity, and moderately resistant fluopyram phenotypes, respectively. The SDHD mutant had reduced sensitivity to fluopyram and penthiopyrad but was highly resistant to fluxapyroxad. The discrepancies of cross-resistance patterns between SDHIs suggest that their binding sites in complex II may differ slightly and that additional mechanisms of resistance to these compounds are likely involved. Ultimately, the findings of this study should lead to the rational and sustained deployment of new SDHIs in Alternaria late blight spray programs.

Spilocaea oleagina in Olive Groves of Southern Spain: Survival, Inoculum Production, and Dispersal

Olive scab caused by the mitosporic fungus Spilocaea oleagina is the most important foliar disease of olive. Limited information is available on pathogen survival and disease epidemiology; however, this information is essential for development of new control strategies. Pathogen survival and inoculum production on infected olive leaves and conidial dispersal were evaluated during 4 years in an olive orchard of the susceptible 'Picual' in southern Spain. Infected leaves in the tree canopy were important for pathogen survival and conidia production. The number of conidia per square centimeter of scab lesion and their viability varied greatly throughout the seasons and between years; conidial density in lesions was highest (about 1 to 5 × 10⁵ conidia cm^-2) from November to February in favorable years. Conidial density declined sharply in other periods of the year (becoming zero in summer) or in less favorable years. The pathogen did not form new conidia in scab lesions, although some pseudothecia-like structures and chlamydospores were detected on fallen leaves. Under humid conditions, the pathogen could not be detected on fallen leaves after 3 months because the leaves were colonized by saprophytic fungi. The dispersal of conidia as a function of distance from infected leaves in the tree canopy was well described by an exponential model which, together with the lack of conidia in a Burkard spore trap, showed that conidia were mainly rain-splash dispersed. Some trapped conidia were attached to olive leaf trichomes, suggesting that detached trichomes might enhance wind dispersal of conidia.

Mummified fruit as a source of inoculum and disease dynamics of olive anthracnose caused by Colletotrichum spp

Anthracnose, caused by Colletotrichum spp., is a destructive disease of olive fruit worldwide. The objective of this study was to investigate the influence of agronomical and weather factors on inoculum production using detached olive fruit and on the development of epidemics in the field. The pathogen produced very large numbers of conidia on rotted (>1.87 × 10(8) conidia/fruit) or mummified (>2.16 × 10(4) conidia/fruit) fruit under optimal conditions. On mummified fruit, conidial production was highest on mummies incubated at 20 to 25°C and 96 h of wetness. Repeated washings of mummies reduced conidial production until it was very low after five washings. When mummies were placed in the tree canopy, conidial production was not reduced after 6 months (May to October); but, when they were held on the soil or buried in the soil, conidial production comparatively decreased up to 10,000 times. Anthracnose epidemics on susceptible 'Hojiblanca' and 'Picudo' during three seasons (2005-08) were influenced by rainfall, temperature, and fruit ripening, and had three main phases: the latent period (May to October); the onset of the epidemic, which coincided with the beginning of fruit ripening (early November); and disease development, which was predicted by the Weibull model (November to March). No epidemics developed on the susceptible cultivars during the driest season (2007-08) or on the resistant 'Picual' olive during any of the three seasons. These results provide the basis for a forecasting system of olive anthracnose which could greatly improve the management of this disease.

Effect of temperature, wetness duration, and planting density on olive anthracnose caused by Colletotrichum spp

The influence of temperature, wetness duration, and planting density on infection of olive fruit by Colletotrichum acutatum and C. simmondsii was examined in laboratory and field experiments. Detached olive fruit of 'Arbequina', 'Hojiblanca', and 'Picual' were inoculated with conidia of several isolates of the pathogen and kept at constant temperatures of 5 to 35°C in humid chambers. Similarly, potted plants and stem cuttings with fruit were inoculated and subjected to wetness periods of 0 to 48 h. Infection occurred at 10 to 25°C, and disease severity was greater and the mean latent period was shorter at 17 to 20°C. Overall, C. acutatum was more virulent than C. simmondsii at temperatures <25°C. When temperature was not a limiting factor, disease severity increased with the wetness period from 0 to 48 h. Disease severity was modeled as a function of temperature and wetness duration; two critical fruit incidence thresholds were defined as 5 and 20%, with wetness durations of 1.0 and 12.2 h at the optimum temperature. In the field, anthracnose epidemics progressed faster in a super-high-density planting (1,904 olive trees/ha) than in the high-density plantings (204 to 816 olive trees/ha) and caused severe epidemics in the super-high-density planting even with the moderately resistant Arbequina. Data in this study will be useful for the development of a forecasting system for olive anthracnose epidemics.

First Report of Botryosphaeria obtusa as Causal Agent of Olive Tree Branch Dieback in Tunisia

A branch dieback of olive trees (Olea europaea L. cv. Manzanilla de Sevilla) was observed in 2010 in an orchard (50 ha), located in the Testour region of northern Tunisia. More than 50% of trees were severely damaged by the disease. Symptomatic trees presented dead branches and wilted leaves, which remained attached to the shoots, and the affected tissues appeared abnormally dark compared with the inner bark of healthy branches. Numerous pycnidia were observed on the surface of the infected branches. For diagnosis, symptomatic stems were collected and small pieces of discolored tissues were excised from lesion margins, surface sterilized in 0.5% sodium hypochlorite for 1 min, rinsed and dried on sterilized filter paper, then placed on acidified Difco potato dextrose agar plates (APDA; 2.5 ml of 25% lactic acid per liter). Plates were incubated at 25°C for 4 to 5 days, and hyphal tips from developing fungal colonies were transferred to PDA and placed under fluorescent light (12 h/day). A fastgrowing, pycnidia-producing fungus was consistently isolated, with conidia exuding onto the agar surface of 10-day-old cultures. On the basis of colony characteristics, isolates were identified as Botryosphaeria obtusa (3). Conidia were large, dark brown, aseptate, rounded at both ends or truncate at base, and 25 to 26.8 × 10.5 to 12.03 μm. Pathogenicity tests were performed on detached stems of cv. Manzanilla by 7-mm diameter mycelial plugs cut from actively growing cultures of the fungus. Stems (30 cm length) were cleaned, surface sterilized with sodium hypochlorite (0.25% for 2 min), and wounded with a sterilized scalpel. Mycelial disks were placed over wounds and wrapped with Parafilm to prevent desiccation. Control stems were mock inoculated with sterile agar plugs. Inoculated and control stems were placed in polyethylene boxes and incubated at 25°C. After 45 days, inoculated stems developed brown discoloration, and small dark pycnidia appeared on stem surfaces. Controls remained healthy. Koch's postulates were verified by isolating the fungus from symptomatic stems. To confirm the identification, DNA of one isolate was extracted and the fungal primers ITS1 and ITS4 (4) were used to amplify the internal transcribed spacer region of rDNA. Purified amplicons were sequenced and a BLAST search of the GenBank database revealed 99% homology with B. obtusa isolate HO166525.1. The anamorph of the fungus, Diplodia seriata, has been recognized as the cause of fruit rot of olive (1) and branch canker or dieback (2). To our knowledge, this is the first report of a canker disease of olive trees caused by B. obtusa in Tunisia. References: (1) J. Moral et al. Plant Dis. 92:311, 2008. (2) J. Moral et al. Phytopathology 100:1340, 2010. (3) A. Taylor et al. Australas. Plant Pathol. 34:187, 2005. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

Factors Affecting Infection and Disease Development on Olive Leaves Inoculated with Fusicladium oleagineum

Infection and development of olive scab disease, caused by Fusicladium oleagineum, were evaluated on detached leaves and potted plants of the susceptible cultivar Picual in growth chambers and a shadehouse. An inoculum dose of 1 × 10⁵ conidia per ml was selected from a range of densities tested, and it was used for all experiments. Infection occurred from 5 to 25°C, and disease severity was the greatest at ~20°C for wetness durations of 12 to 24 h and at ~15°C for longer durations. Based on a generalized form of the Analytis Beta model, the optimum temperature and minimum wetness duration for infection were 15.5°C and 11.9 h. Dry periods ≤78 h immediately after inoculation did not reduce disease incidence but did reduce disease severity. Disease severity was negatively correlated with leaf age. Disease incubation period was positively correlated with leaf age, with a minimum incubation period of 28 days in the youngest leaves. Inoculated plants that were incubated in a growth chamber or in a shadehouse had the same level of infection, but disease severity was lower in plants incubated in the growth chamber because many infections remained latent for 6 months after inoculation. The data in this study will be useful for the development of a forecasting system for olive scab epidemics.

First Report of Fruit Rot of Olives Caused by Botryosphaeria dothidea in Tunisia

During the summer of 2010, unfamiliar symptoms of fruit rot were frequently observed on different Tunisian olive (Olea europaea) cultivars. These symptoms appeared to be associated with the damage caused by the olive fruit fly (Bactrocera oleae). At first, infected olives showed a brown color and then fruits begin to depress until they become completely mummified and fall immaturely. This problem was more pronounced on table olive cultivars (Ascolana, Meski, and Picholine) in the northern Tunisian regions (Nabeul), with an infection incidence of 65%. Infected Ascolana olives were disinfected with 70% ethanol for 2 min, rinsed in sterile distilled water, and air dried. Several pieces were cut and placed on acidified (2.5 ml of a 25% [vol/vol] solution of lactic acid per liter of medium) potato dextrose agar medium (PDA). All plates were incubated at 25°C for 4 days under continuous fluorescent light. A fast-growing fungus with an abundant, aerial mycelium, which was gradually veering from white to dark gray, was constantly isolated. On the reverse side of the colonies, an olive green coloration spread to the edge and became darker from the center until the underside was completely black. Conidia produced on the PDA plate were hyaline, single or double cell, ellipsoid, with a subobtuse apex and a truncate base, and averaged 22.70 × 5.32 μm. Conidiophores were hyaline, cylindrical, smooth, branched at the base, with an average of 14 to 24 × 2 to 3 μm. Pathogenicity of an isolate was conducted by dipping 20 olives wounded by a sterilized scalpel in a conidial suspension (10⁵ conidia/ml), covering inoculated olives with moisture filter paper, and incubating them in a polyethylene bag under darkness at 25°C. Controls however, were wounded and dipped in sterile distillated water. Seven days after the inoculation, olives showed a brown color covering half of the fruit. Later (15 days after), this browning was accentuated and several black pycnidia were observed. Forty days after inoculation, fruits were completely dried out and the kernel was already appearing. Controls, however, remained totally healthy. Koch's postulates was then verified and showed that pure cultures were obtained after reisolations from inoculated olives, whereas the controls were free of the fungus. BLAST analysis of the internal transcribed spacer region (ITS) of rDNA of one isolate showed 99% identity with the ITS sequence of Botryosphaeria dothidea (GenBank Accession No. FM955381.1). Species of the family of Botryosphaeriaceae are common pathogens causing fruit rot and dieback of many woody plants (3). Drupe rot problem caused by B. dothidea was reported on olives in Greece (4) and southern Italy (2). It was reported that the fungus invades the drupes through the wounds caused by the olive fruit fly and may even be transmitted by it (1), and recently Moral et al. (3) suggested that the olive fruit fly is essential for the initiation of the disease on the fruit. To our knowledge, this is the first report of fruit rot of olives caused by B. dothidea in Tunisia. References: (1) N. González et al. Bol. San. Veg. Plagas 32:709, 2006. (2) C. Lazzizera et al. Plant Pathol. 57:948, 2008. (3) J. Moral et al. Phytopathology 100:1340, 2010. (4) A. J. L Phillips et al. Mycopathology 159:433, 2005.

Characterization and pathogenicity of Botryosphaeriaceae species collected from olive and other hosts in Spain and California

Species in the family Botryosphaeriaceae are common pathogens causing fruit rot and dieback of many woody plants. In this study, 150 Botryosphaeriaceae isolates were collected from olive and other hosts in Spain and California. Representative isolates of each type were characterized based on morphological features and comparisons of DNA sequence data of three regions: internal transcribed spacer 5.8S, β-tubulin, and elongation factor. Three main species were identified as Neofusicoccum mediterraneum, causing dieback of branches of olive and pistachio; Diplodia seriata, causing decay of ripe fruit and dieback of olive branches; and Botryosphaeria dothidea, causing dalmatian disease on unripe olive fruit in Spain. Moreover, the sexual stage of this last species was also found attacking olive branches in California. In pathogenicity tests using unripe fruit and branches of olive, D. seriata isolates were the least aggressive on the fruit and branches while N. mediterraneum isolates were the most aggressive on both tissues. Isolates of B. dothidea which cause dalmatian disease on fruit were not pathogenic on branches and only weakly aggressive on fruit. These results, together with the close association between the presence of dalmatian disease symptoms and the wound created by the olive fly (Bactrocera oleae), suggest that the fly is essential for the initiation of the disease on fruit. Isolates recovered from dalmatian disease symptoms had an optimum of 26°C for mycelial growth and 30°C for conidial germination, suggesting that the pathogen is well adapted to high summer temperatures. In contrast, the range of water activity in the medium for growth of dalmatian isolates was 0.93 to 1 MPa, which was similar to that for the majority of fungi. This study resolved long-standing questions of identity and pathogenicity of species within the family Botryosphaeriaceae attacking olive trees in Spain and California.

First Report of Verticillium Wilt of Pistachio Caused by Verticillium dahliae in Spain

Pistachio (Pistacia vera L.) trees in the Castilla La Mancha and Andalusia regions of central and southern Spain are grown close to olive orchards, which are often severely affected by Verticillium dahliae. During the last decade, wilt and death of one or several branches have been observed on pistachio (cv. Kerman) scions grafted on rootstock (P. terebinthus). Discoloration of vascular tissue was occasionally observed. In five surveyed orchards, incidence of affected trees was less than 2%. Wood chips with the bark removed from symptomatic trees were washed in running tap water, surface disinfested in 0.5% sodium hypochlorite for 1 min, and placed onto potato dextrose agar plates incubated at 25°C in the dark. Isolates were identified as V. dahliae on the basis of the characteristics of microsclerotia, conidiophores, and conidia. V. dahliae isolate V117 from olive was used as reference (1). The fungus was also isolated from soil in pistachio orchards using wet sieving and a modified sodium polypectate agar medium (1). Inoculum density varied from 0 to 4.73 microsclerotia per gram of soil. P. terebinthus seedlings were inoculated with two isolates of V. dahliae from pistachio trees by injecting the stems with 50 μl of a conidial suspension (10⁷ conidia per ml) (2). Wilt symptoms of varying severity developed in 12 and 15 seedlings of the 20 pistachio seedlings inoculated with each of two isolates. No symptoms developed on the control seedlings. The pathogen was recovered from stem tissues of inoculated plants. To our knowledge, this is the first report of Verticillium wilt of pistachio in Spain. This study demonstrates the susceptibility of certain rootstocks to V. dahliae and the importance of using resistant rootstocks, such as UCBI (2), in pistachio plantations established on soils infested by V. dahliae. References: (1) F. J. López-Escudero and M. A. Blanco-López. Plant Dis. 91:1372, 2007. (2) D. P. Morgan et al. Plant Dis. 76:310, 1992.

Assessing the Susceptibility of Olive Cultivars to Anthracnose Caused by Colletotrichum acutatum

Selected olive (Olea europaea) cultivars were tested in the field and laboratory for their relative susceptibility to anthracnose caused by Colletotrichum acutatum. A rating scale to assess fruit-rot incidence in naturally infected trees was validated by comparing ratings with direct counts of affected fruit. Fruit-rot incidence varied greatly among 20 cultivars and was correlated with the severity of branch dieback symptoms that developed after fruit-rot epidemics. For determining whether artificial inoculation can be used to predict anthracnose susceptibility in the orchard, detached fruit of 12 cultivars were inoculated with C. acutatum and fruit-rot severity was assessed periodically. Progress of disease severity over time fit the logistic function for all cultivars. The best correlation between fruit-rot incidence in the field and disease severity on inoculated fruit was obtained using a disease susceptibility index that integrated the maximum disease progress rate and the estimated time to reach 50% disease severity. Based on field observations and laboratory data on susceptibility to anthracnose, 21 cultivars were classified into three groups: highly susceptible (Cornicabra, Hojiblanca, Lechín de Sevilla, Manzanilla de Sevilla, Morona, Ocal, Picudo, and Verdial de Huévar); moderately susceptible (Arbequina, Arbosana, Morrut, Pajarero, and Villalonga); and resistant (Blanqueta, Empeltre, Frantoio, Koroneiki, Leccino, Morona-D, Picual, and Razzola). The assessment method may be useful to screen olive cultivars for anthracnose resistance.

Elucidation of the disease cycle of olive anthracnose caused by Colletotrichum acutatum

Anthracnose, caused by Colletotrichum acutatum and C. gloeosporioides, is a major fungal disease of olive in many countries. In Spain, the disease has been associated only with a characteristic rot and mummification of mature fruit. The purpose of this study was to determine whether C. acutatum could infect other plant tissues that may serve as sources of inoculum for anthracnose epidemics. Inoculations of young plants or detached leaves and field observations demonstrated that flowers and immature olive fruit are susceptible to the pathogen. Flower infection caused blight of inflorescences and infection of developing fruit. Immature fruit were infected in all phenological stages, although infection remained latent for 7 to 8 months, until the onset of fruit ripening. Fruit susceptibility increased and latent period decreased with maturity. Fruit were required for symptom development on inoculated plants. Plants without fruit were infected but they did not show any disease symptoms. Only plants with rotten fruit developed leaf wilting and branch dieback symptoms several weeks later. These results, together with the low level of pathogen isolation from affected leaves and branches and the toxicity of sterile fungal extracts to olive cuttings, suggest that a toxic substance produced by C. acutatum in rotten fruit may account for this syndrome. Both disease syndromes, fruit rot and branch dieback, developed in several olive cultivars, which were equally susceptible to the pathogen. However, olive cultivars differed in their response to flower and fruit infection. Latent infection of developing fruit during the spring may permit survival of the pathogen during the hot and dry summer and serve as an inoculum source for anthracnose epidemics that develop on ripening fruit in autumn.

Influence of Fruit Maturity, Cultivar Susceptibility, and Inoculation Method on Infection of Olive Fruit by Colletotrichum acutatum

Detached olive (Olea europaea) fruit inoculated with isolates of Colletotrichum acutatum, causal agent of olive anthracnose, were used to study host-pathogen interactions. Fruit susceptibility increased with increasing fruit maturity. Wounded fruit were more severely affected than nonwounded fruit; however, the wound effect depended on cultivar and inoculation method. Severity of fruit infection increased with inoculum density, although this effect also depended on fruit maturity and cultivar susceptibility. The susceptibility of selected olive cultivars to anthracnose under field conditions correlated well with the response of immature fruit under controlled conditions. As fruit matured, there were fewer differences among cultivars. Based on these results, an inoculation method using immature green fruit and high inoculum densities (10⁵ to 10⁶ conidia/ml) sprayed on the fruit has been proposed to evaluate olive cultivars for anthracnose resistance under controlled conditions.

High Susceptibility of Olive Cultivar FS-17 to Alternaria alternata in Southern Spain

Traditional olive orchards in Spain have been planted at a density of 70 to 80 trees per ha with three trunks per tree. During the last decade, the hedgerow orchard, in which planting density is approximately 2,000 trees per ha, was developed. In 2006 and 2007, we noted a severe outbreak of fruit rot in FS-17, a new cultivar from Italy, in an experimental hedgerow planting in Córdoba, southern Spain. The incidence of fruit rot in 'FS-17' was 80% in January of 2006 and 24% in January of 2007. Cvs. Arbosana, IRTA-i18 (a selected clone from 'Arbequina'), and Koroneiki had no symptoms in either year of the study. Disease incidence in 'Arbequina' was <0.1% only in 2006. Affected fruits were soft with gray-white skin and they eventually mummified. Black-green sporodochia were observed on the surface of diseased fruits. A fungus was isolated from diseased fruits on potato dextrose agar (PDA) and incubated at 22 to 26°C with a 12-h photoperiod. After 8 days of growing on PDA, fungal colonies formed conidial chains having a main axis with up to 10 conidia and secondary and tertiary short branches with two to four conidia. Conidia were obpyriform, ovoid, or ellipsoidal, without a beak or with a short beak, had up to four transverse septa, and measured 11.7 to 24.7 (mean 19.6) μm long and 7.7 to 13.0 (mean 9.6) μm wide at the broadest part of the conidium. The length of the beak of conidia was variable, ranging from 0 to 28.6 (mean 5.5) μm. The fungus was identified as Alternaria alternata (1). Pathogenicity tests were performed by spraying 40 mature fruits of 'FS-17' with a spore suspension (1 × 10⁶ spores per ml). The same number of control fruits was treated with water. After 21 days, inoculated fruit developed symptoms that had earlier been observed in the field. A. alternata was reisolated from lesions on all infected fruits. The fungus was not isolated from any of the control fruits. The experiment was performed twice. The new growing system and the high susceptibility of some olive cultivars, such as FS-17, may result in a high incidence of disease caused by a pathogen that is generally characterized as weakly virulent. To our knowledge, this is the first report of A. alternata causing a severe outbreak of fruit rot on olive trees in the field. References: (1) B. M. Pryor and T. J. Michailides. Phytopathology 92:406, 2002.

First Report of Diplodia seriata, the Anamorph of "Botryosphaeria" obtusa, Causing Fruit Rot of Olive in Spain

In October, 2006, 1,000 olive fruits (Olea europaea) were collected to study latent infections of Colletotrichum spp., causal agent of anthracnose, in an olive orchard in Córdoba Province (southern Spain). The fruits were incubated at 22 to 24°C and 100% relative humidity. Thirteen percent of the fruits showed a black rot that covered part or all of the fruit and pycnidia formed on the fruit surface. The fungus most consistently isolated from affected fruits was identified as Diplodia seriata, the anamorph of "Botryosphaeria" obtusa, by morphological criteria (1). Pathogenicity tests were performed on 50 immature and 50 mature fruits of olive cv. Hojiblanca. The fruits were washed in sterilized water with Tween 20 at 20 μl/liter and surface sterilized in 20% sodium hypochlorite for 2 min. Twenty-five of the immature and 25 mature fruits were wounded with a sterile 0.5-mm-diameter needle, inoculated by immersion in aqueous conidial suspensions (2.2 × 10⁵ conidia ml^-1) for 30 min. The same number of immature and mature fruits, wounded and unwounded, were treated only with sterilized Tween 20 water and served as the control. All fruit were incubated at 22 to 24°C and 100% relative humidity. The experiment was repeated twice. Eight days after inoculation, 75% of the mature inoculated fruits showed a general rot with pycnidia developing on the surface of the fruit. After 20 days, the first symptoms of disease were observed on immature olive fruits (2%) and all mature fruits. After 50 days, only 14% of immature inoculated fruits exhibited symptoms of the disease. The fungus caused mummification of mature fruits. D. seriata was reisolated from lesions on all infected fruits. There were no differences in the amount and severity of disease between wounded and unwounded fruits. Control fruits did not display disease symptoms after 50 days. Incidence of olive fruits affected by D. seriata in olive orchards in southern Spain is unknown, although it may be low since it was detected only in 1 of 12 olive orchards sampled for Colletotrichum spp. in 2006. Incidence of fruit rot associated with D. seriata in this orchard was 1.2% of fruits, which also were affected by Colletotrichum. D. seriata has a worldwide distribution and infects numerous fruit trees. In our research, D. seriata is pathogenic on olive fruits but weakly virulent. To our knowledge, this is the first report worldwide of the anamorph of "B." obtusa causing fruit rot on olives. Reference: (1) A. J. L. Phillips et al. Fungal Divers. 25:141, 2007.

The CTFA Evaluation of Alternatives Program: an evaluation of in vitro alternatives to the Draize primary eye irritation test. (Phase III) surfactant-based formulations

The CTFA Evaluation of Alternatives Program is an evaluation of the relationship between data from the Draize primary eye irritation test and comparable data from a selection of promising in vitro eye irritation tests. In Phase III, data from the Draize test and 41 in vitro endpoints on 25 representative surfactant-based personal care formulations were compared. As in Phase I and Phase II, regression modelling of the relationship between maximum average Draize score (MAS) and in vitro endpoint was the primary approach adopted for evaluating in vitro assay performance. The degree of confidence in prediction of MAS for a given in vitro endpoint is quantified in terms of the relative widths of prediction intervals constructed about the fitted regression curve. Prediction intervals reflect not only the error attributed to the model but also the material-specific components of variation in both the Draize and the in vitro assays. Among the in vitro assays selected for regression modeling in Phase III, the relationship between MAS and in vitro score was relatively well defined. The prediction bounds on MAS were most narrow for materials at the lower or upper end of the effective irritation range (MAS = 0-45), where variability in MAS was smallest. This, the confidence with which the MAS of surfactant-based formulations is predicted is greatest when MAS approaches zero or when MAS approaches 45 (no comment is made on prediction of MAS > 45 since extrapolation beyond the range of observed data is not possible). No single in vitro endpoint was found to exhibit relative superiority with regard to prediction of MAS. Variability associated with Draize test outcome (e.g. in MAS values) must be considered in any future comparisons of in vivo and in vitro test results if the purpose is to predict in vivo response using in vitro data.