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

Secondary metabolites produced by four Colletotrichum species in vitro and on fruits of diverse olive cultivars

This study was aimed to characterize the secondary metabolites produced by four Colletotrichum species, C. acutatum, C. gloeosporioides, C. godetiae and C. karsti, both in vitro, on potato dextrose agar (PDA) and oatmeal agar (OA), and during the infection process of fruits of four olive cultivars differing in susceptibility to anthracnose, 'Coratina' and 'Ottobratica', both susceptible, 'Frantoio' and 'Leccino', both resistant. The metabolites were extracted from axenic cultures after seven days incubation and from olives inoculated singularly with each Colletotrichum species, at three different times, 1, 3 and 7 days post inoculation (dpi). They were identified using the UHPLC-QTOF-MS analysis method. In total, as many as 45 diverse metabolites were identified. Only 10 metabolites were present in both fruits and axenic cultures while 19 were found exclusively on olives and 16 exclusively in axenic cultures. The identified metabolites comprised fatty acid, phenolics, pyrones, sterols, terpenes and miscellaneous compounds. Each Colletotrichum species produced a different spectrum of metabolites depending on the type of matrices. On artificially inoculated olives the severity of symptoms, the amount of fungal secondary metabolites and their number peaked 7 dpi irrespective of the cultivar susceptibility and the virulence of the Colletotrichum species.

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.

Oviposition Deterrent Activity of Fungicides and Low-Risk Substances for the Integrated Management of the Olive Fruit Fly Bactrocera oleae (Diptera, Tephritidae)

Simple Summary

The olive fruit fly Bactrocera oleae is a very common pest infesting olive orchards wherever they are cultivated, representing the greatest threat to olive production and oil quality. Although broad-spectrum insecticides are often used to protect olive crops against B. oleae, there is increasing concern about their effects on the environment and human health. An important tool in integrated olive fly management could be the use of products with a repellency and oviposition deterrence effect. This research yielded experimental evidence of significant oviposition deterrent activity on the olive fly as side effects of substances used in olive growing such as fungicides or plant biostimulants, highlighting the potential use of these products in B. oleae management.

Abstract

The control of Bactrocera oleae is fundamental to decreasing the significant production loss in olive cultivation. However, traditional containment based on the use of synthetic insecticides has been encountering serious limitations due to their negative effect on human health and the environment. Within the scope of integrated olive fly management, the use of products with repellency and oviposition deterrent activity might represent a more eco-friendly solution. In this study, we tested the oviposition deterrent activity of some commercial formulations already used in olive tree crops as fungicides (copper oxychloride, dodine, mancozeb, pyraclostrobin and difeconazole) and plant bio-stimulants (tannins, clay, flavonoids and a zinc-copper-citric acid biocomplex). The trials were conducted testing the oviposition behavior of mated olive fly females in both choice and no-choice assays. Our results showed that most of the substances have affected the ovipositional activity of the olive fly, except for difeconazole. Moreover, some products (copper oxychloride, flavonoids and tannins) have proven to differently influence the flies’ oviposition comparing the two tests. The repellent effect of these commercial products should be further studied to prove whether the repellency was due either to the active ingredient or to the co-formulants, and to assess their effect in the open field.

Fungal Communities Associated with Peacock and Cercospora Leaf Spots in Olive

Venturia oleaginea and Pseudocercospora cladosporioides are two of the most important olive fungal pathogens causing leaf spots: peacock spot, and cercosporiosis, respectively. In the present study, fungal communities associated with the presence of these pathogens were investigated. Overall, 300 symptomatic and asymptomatic trees from different cultivars were sampled from Alentejo, Portugal. A total of 788 fungal isolates were obtained and classified into 21 OTUs; Ascomycota was clearly the predominant phylum (96.6%). Trees from cultivar 'Galega vulgar' showed a significant higher fungal richness when compared to 'Cobrançosa', which in turn showed significant higher values than 'Picual'. Concerning plant health status, symptomatic plants showed significant higher fungal richness, mainly due to the high number of isolates of the pathogens V. oleaginea and P. cladosporioides. In terms of fungal diversity, there were two major groups: ca. 90% of the isolates found in symptomatic plants belonged to V. oleaginea, P. cladosporioides, Chalara sp., and Foliophoma sp. while ca. 90% of the isolates found in asymptomatic plants, belonged to Alternaria sp. and Epicoccum sp. This study highlights the existence of different fungal communities in olive trees, including potential antagonistic organisms that can have a significant impact on diseases and consequently on olive production.

Olive anthracnose: a yield- and oil quality-degrading disease caused by several species of Colletotrichum that differ in virulence, host preference and geographical distribution

Olive anthracnose causes fruit rot leading to its drop or mummification, resulting in yield losses and the degradation of oil quality.

TAXONOMY AND DISTRIBUTION

The disease is caused by diverse species of Colletotrichum, mostly clustering in the C. acutatum species complex. Colletotrichum nymphaeae and C. godetiae are the prevalent species in the Northern Hemisphere, whereas C. acutatum sensu stricto is the most frequent species in the Southern Hemisphere, although it is recently and quickly emerging in the Northern Hemisphere. The disease has been reported from all continents, but it attains higher incidence and severity in the west of the Mediterranean Basin, where it is endemic in traditional orchards of susceptible cultivars.

LIFE CYCLE

The pathogens are able to survive on vegetative organs. On the fruit surface, infections remain quiescent until fruit maturity, when typical anthracnose symptoms develop. Under severe epidemics, defoliation and death of branches can also occur. Pathogen species differ in virulence, although this depends on the cultivar.

CONTROL

The selection of resistant cultivars depends strongly on pathogen diversity and environmental conditions, posing added difficulties to breeding efforts. Chemical disease control is normally achieved with copper-based fungicides, although this may be insufficient under highly favourable disease conditions and causes concern because of the presence of fungicide residues in the oil. In areas in which the incidence is high, farmers tend to anticipate harvest, with consequences in yield and oil characteristics.

CHALLENGES

Olive production systems, harvest and post-harvest processing have experienced profound changes in recent years, namely new training systems using specific cultivars, new harvest and processing techniques and new organoleptic market requests. Changes are also occurring in both the geographical distribution of pathogen populations and the taxonomic framework. In addition, stricter rules concerning pesticide use are likely to have a strong impact on control strategies. A detailed knowledge of pathogen diversity, population dynamics and host-pathogen interactions is basal for the deployment of durable and effective disease control strategies, whether based on resistance breeding, agronomic practices or biological or chemical control.

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.