Genetic Diversity and Pathogenicity of Botryosphaeriaceae Species Associated with Symptomatic Citrus Plants in Europe

Genetic diversity and population structure of Botryosphaeria dothidea and Neofusicoccum parvum on English walnut (Juglans regia L.) in France

Botryosphaeriaceae species are the major causal agents of walnut dieback worldwide, along with Diaporthe species. Botryosphaeria dothidea and Neofusicoccum parvum are the only two Botryosphaeriaceae species associated with this recently emergent disease in France, and little is known about their diversity, structure, origin and dispersion in French walnut orchards. A total of 381 isolates of both species were genetically typed using a sequence-based microsatellite genotyping (SSR-seq) method. This analysis revealed a low genetic diversity and a high clonality of these populations, in agreement with their clonal mode of reproduction. The genetic similarity among populations, regardless of the tissue type and the presence of symptoms, supports the hypothesis that these pathogens can move between fruits and twigs and display latent pathogen lifestyles. Contrasting genetic patterns between N. parvum populations from Californian and Spanish walnut orchards and the French ones suggested no conclusive evidence for pathogen transmission from infected materials. The high genetic similarity with French vineyards populations suggested instead putative transmission between these hosts, which was also observed with B. dothidea populations. Overall, this study provides critical insight into the epidemiology of two important pathogens involved in the emerging dieback of French walnut orchards, including their distribution, potential to mate, putative origin and disease pathways.

Diplodia seriata Isolated from Declining Olive Trees in Salento (Apulia, Italy): Pathogenicity Trials Give a Glimpse That It Is More Virulent to Drought-Stressed Olive Trees and in a Warmth-Conditioned Environment

The fungi Botryosphaeriaceae are involved in olive declines in both the world hemispheres and in all continents where this species is cultivated. In Salento (Apulia, Italy), the Botryosphaeriaceae Neofusicoccum mediterraneum and N. stellenboschiana have been reported as the agents of a branch and twig dieback that overlaps with olive quick decline syndrome caused by Xylella fastidiosa subsp. pauca. In this study, we report the finding of Diplodia seriata, another Botryosphaeriaceae species, in Salento in Xylella fastidiosa-infected olive trees affected by symptoms of branch and twig dieback. Given that its presence was also reported in olive in the Americas and in Europe (Croatia) with different degrees of virulence, we were prompted to assess its role in the Apulian decline. We identified representative isolates based on morphological features and a multilocus phylogeny. In vitro tests showed that the optimum growth temperature of the isolates is around 25-30 °C, and that they are highly thermo-tolerant. In pathogenicity trials conducted over eleven months, D. seriata expressed a very low virulence. Nonetheless, when we imposed severe water stress before the inoculation, D. seriata significatively necrotized bark and wood in a time frame of 35 days. Moreover, the symptoms which resulted were much more severe in the trial performed in summer compared with that in autumn. In osmolyte-supplemented media with a water potential from -1 to -3 Mpa, the isolates increased or maintained their growth rate compared with non-supplemented media, and they also grew, albeit to a lesser extent, on media with a water potential as low as -7 Mpa. This suggests that olives with a low water potential, namely those subjected to drought, may offer a suitable environment for the fungus' development. The analysis of the meteorological parameters, temperatures and rainfall, in Salento in the timeframe 1989-2023, showed that this area is subjected to a progressive increase of temperature and drought during the summer. Thus, overall, D. seriata has to be considered a contributor to the manifestation of branch and twig dieback of olive in Salento. Coherently with the spiral decline concept of trees, our results suggest that heat and drought act as predisposing/inciting factors facilitating D. seriata as a contributor. The fact that several adverse factors, biotic and abiotic, are simultaneously burdening olive trees in Salento offers a cue to discuss the possible complex nature of the olive decline in Salento.

Phylogenetic and Pathogenic Evidence Reveals Novel Host-Pathogen Interactions between Species of Lasiodiplodia and Citrus latifolia Dieback Disease in Southern Mexico

Mexico ranks second in the world for Persian lime (Citrus latifolia) exports, making it the principal citrus exporter within the national citrus industry, exporting over 600,000 tons per year. However, diseases are the main factor reducing production, resulting in significant economic losses. Among these diseases, fungal diseases like dieback, caused by species of Lasiodiplodia, are an emerging issue in Persian lime. Symptoms include gummosis, twig and branch dieback, cankers, the necrosis of bark and wood, fruit mummification, and tree decline. The aim of this study was to investigate the occurrence and pathogenicity of the fungal species associated with twig and branch dieback, cankers, and decline of Persian lime trees in southern Mexico, and to elucidate the current status of the Lasiodiplodia species causing the disease in Mexico. During June, July, and August of 2023, a total of the 9229 Persian lime trees were inspected across 230 hectares of Persian lime orchards in southern Mexico, and symptoms of the disease were detected in 48.78% of the trees. Branches from 30 of these Persian lime trees were collected. Fungal isolates were obtained, resulting in a collection of 40 strains. The isolates were characterized molecularly and phylogenetically through the partial regions of four loci: the internal transcribed spacer region (ITS), the β-tubulin gene (tub2), the translation elongation factor 1-alpha gene (tef1-α), and the DNA-directed RNA polymerase II second largest subunit (rpb2). Additionally, pathogenicity was assessed, successfully completing Koch's postulates on both detached Persian lime branches and certified 18-month-old Persian lime plants. Through multilocus molecular phylogenetic identification, pathogenicity, and virulence tests, five species were identified as causal agents: L. iraniensis, L. lignicola, L. mexicanensis, L. pseudotheobromae, and L. theobromae. This study demonstrates that in southern Mexico, at least five species of the genus Lasiodiplodia are responsible for dieback in Persian lime. Additionally, this is the first report of L. lignicola and L. mexicanensis as causal agents of the disease in citrus, indicating novel host interactions between species of Lasiodiplodia and C. latifolia.

Biocontrol of almond canker diseases caused by Botryosphaeriaceae fungi

BACKGROUND

Botryosphaeria dieback is a canker disease caused by fungal species of the Botryosphaeriaceae family that threatens almond productivity. The most common control measure to prevent canker development is the application of fungicides which are being phased out by European Union regulations. In the present study, two sets of bacterial strains were evaluated for their antifungal activity against pathogenic Botryosphaeriaceae species through in vitro and in vivo antagonism assays.

RESULTS

The rhizospheric bacteria Pseudomonas aeruginosa AC17 and Bacillus velezensis ACH16, as well as the endophytic bacteria Bacillus mobilis Sol 1-2, respectively inhibited 87, 95, and 63% of the mycelial growth of Neofusicoccum parvum, Botryosphaeria dothidea, Diplodia seriata, and Macrophomina phaseolina. Additionally, they significantly reduced the length of lesions caused by N. parvum and B. dothidea in artificially inoculated detached almond twigs. All these bacterial strains produce hydrolytic enzymes that are able to degrade the fungal cell wall. P. aeruginosa AC17 also produces toxic volatile compounds, such as hydrogen cyanide. This strain was the most effective in controlling Botryosphaeria dieback in planta under controlled conditions at a level similar to the biocontrol agent Trichoderma atroviride and standard chemical fungicide treatments.

CONCLUSION

Pseudomonas aeruginosa AC17 is the best candidate to be considered as a potential biocontrol agent against Botryosphaeriaceae fungi affecting almond. © 2023 Society of Chemical Industry.

Characterization and Pathogenicity of Fungal Species Associated with Dieback of Apple Trees in Northern Italy

Severe dieback symptoms were recently observed on apple (Malus × domestica) trees in Northern Italy, representing a growing concern for producers. Surveys were conducted over a 3-year period (2019 to 2021), and five apple orchards, from 5 to 12 years old, were monitored. A total of 33 fungal isolates isolated from symptomatic plants was selected for characterization. The species identification was achieved through multilocus phylogenetic analyses performed on sequences of three genomic loci (ITS, tub2, and tef1). Morphological features were assessed, and the average growth rate at different temperatures was determined. Seven species were identified in association with dieback of apple trees: Botryosphaeria dothidea, Cadophora luteo-olivacea, Diaporthe rudis, Diplodia seriata, Eutypa lata, Kalmusia longispora, and Paraconiothyrium brasiliense. All the species were pathogenic when inoculated on healthy apple plants. B. dothidea resulted in the most aggressive infections. This study provides an insight into the fungal species diversity associated with apple dieback and provides basis for further investigations to assess the phytosanitary status of plant materials to recommend and implement effective management strategies.

The chemical constituents of endophytic fungus Nigrospora chinensis of Gannan navel orange

A new drimane sesquiterpene 11-methoxyl-danilol (1) was obtained from endophytic fungus Nigrospora chinensis of Gannan navel orange pulp. Its structure was established to possess a natural rarely-occurring tricyclic acetal fused ring system by means of spectroscopic data analyses. Meanwhile, five known compounds danilol (2), redoxcitrinin (3), euphorbol (4), ergosta-7,24(24')-dien-3β-ol (5), and ergosta-4,6,8(14),22-tetraen-3-one (6) were also co-isolated in this fungus. The results of antibacterial and cytotoxic activity screenings showed that compound 5 displayed antibacterial activities against Staphylococcus aureus and MRSA (methicillin-resistant S. aureus) with MIC value of 50 μg/mL. [Figure: see text].

Isolation, identification, and antibacterial evaluation of endophytic fungi from Gannan navel orange

Gannan navel orange is a famous brand in China but the isolation of its endophytic fungi was rarely reported. In this study, a total of 54 strains of endophytic fungi were successfully isolated from the pulp, peel, twig, and leaf of Gannan navel orange; they were successfully identified to belong to 17 species of 12 genera. All these strains were fermented using potato-dextrose agar (PDA) medium, and their secondary metabolites were then extracted with ethyl acetate (EtOAc). The antibacterial assays of Escherichia coli (E. coli), methicillin-resistant Staphylococcus aureus (MRSA), and Xanthomonas citri subsp. citri (Xcc) were also performed for the EtOAc extracts of these strains. As a result, the extracts of both Geotrichum sp. (gc-1-127-30) and Diaporthe biconispora (gc-1-128-79) demonstrated significant antibacterial activities against Xcc, and the MIC value for the extract of Colletotrichum gloeosporioides against MRSA was low to 62.5 μg/mL. Moreover, the chemical components of the extracts of Colletotrichum sp., Diaporthe biconispora, and Annulohypoxylon atroroseum were primarily investigated, and they successfully led to the isolation of 24 compounds involving a new botryane sesquiterpene. Among the isolated products, compound 2 showed significant inhibitory activities toward SA, MRSA, E. coli, and Xcc with MIC values of 12.5, 3.1, 125, and 12.5 μg/mL, respectively. This study revealed that the endophytic fungi of Gannan navel orange showed high potency to produce secondary metabolites with significant antibacterial effects.

Duplex Real-Time PCR Assays for the Simultaneous Detection and Quantification of Botryosphaeriaceae Species Causing Canker Diseases in Woody Crops

Woody canker diseases caused by fungi of the Botryosphaeriaceae family are producing increasing losses in many economically important woody crops, including almond. To develop a molecular tool for the detection and quantification of the most aggressive and threatening species is of main importance. This will help to prevent the introduction of these pathogens in new orchards and to conveniently apply the appropriate control measures. Three reliable, sensitive and specific duplex qPCR assays using TaqMan probes have been designed for the detection and quantification of (a) Neofusicoccum parvum and the Neofusicoccum genus, (b) N. parvum and the Botryosphaeriaceae family and (c) Botryosphaeria dothidea and the Botryosphaeriaceae family. The multiplex qPCR protocols have been validated on artificially and naturally infected plants. Direct systems to process plant materials, without DNA purification, allowed high-throughput detection of Botryosphaeriaceae targets even in asymptomatic tissues. These results validate the qPCR using the direct sample preparation method as a valuable tool for Botryosphaeria dieback diagnosis allowing a large-scale analysis and the preventive detection of latent infection.

Morphology and molecular analyses reveal three new species of Botryosphaeriales isolated from diseased plant branches in China

The Botryosphaeriales represents an ecologically diverse group of fungi, comprising endophytes, saprobes, and plant pathogens. In this study, taxonomic analyses were conducted based on morphological characteristics and phylogenetic analyses of multi-gene sequence data from four loci (ITS, LSU, tef1-α, and tub2). Thirteen isolates obtained from Beijing and Yunnan Province were identified as seven species of Botryosphaeriales, including Aplosporellajaveedii, Dothiorellaalpina, Phaeobotryonaplosporum and Ph.rhois, and three previously undescribed species, namely Aplosporellayanqingensis, Dothiorellabaihuashanensis, and Phaeobotryonplatycladi. Additionally, the new records of Dothiorellaalpina from the host species Populusszechuanica, Phaeobotryonaplosporum from Juglansmandshurica, and Phaeobotryonrhois from Populusalbavar.pyramidalis are included.

Identification and Characterization of Neofusicoccum stellenboschiana in Branch and Twig Dieback-Affected Olive Trees in Italy and Comparative Pathogenicity with N. mediterraneum

For about a decade, olive groves in Apulia (Southern Italy) have been progressively destroyed by Olive Quick Decline Syndrome (OQDS), a disease caused by the bacterium Xylella fastidiosa subsp. pauca (Xfp). Recently, we described an additional wilting syndrome affecting olive trees in that area. The botryosphaeriaceous fungus Neofusicoccum mediterraneum was found associated with the diseased trees, and its high virulence toward olive trees was demonstrated. Given the common features with Branch and Twig Dieback (BTD) of olive tree, occurring in Spain and California, we suggested that the observed syndrome was BTD. During our first survey, we also found a botryosphaeriaceous species other than N. mediterraneum. In the present article, we report the morphological and molecular characterization of this fungal species which we identified as Neofusicoccum stellenboschiana. In the study, we also included for comparison additional N. stellenboschiana isolates obtained from olive trees in Latium and Tuscany region (Central Italy). The occurrence of N. stellenboschiana in olive trees is reported here for the first time in the northern hemisphere. The pathogenicity and virulence were tested in nine inoculation trials, where the Apulian N. stellenboschiana isolate was compared with the isolate from Latium and with the Apulian isolate of N. mediterraneum. Both isolates of N. stellenboschiana proved pathogenic to olive trees. They caused evident bark canker and wood discolouration when inoculated at the base of the stem of two/three-year-old trees and on one-year-old twigs. However, virulence of N. stellenboschiana was significantly lower, though still remarkable, compared with N. mediterraneum in term of necrosis progression in the bark and the wood and capacity of wilting the twigs. Virulence of N. stellenboschiana and N. mediterraneum did not substantially change when inoculations were performed in spring/summer and in autumn, suggesting that these fungal species have the potential to infect and damage olive trees in all seasons. The high thermotolerance of N. stellenboschiana was also revealed with in vitro growth and survival tests. The high virulence of these Botryosphaeriaceae species highlights their contribution in BTD aetiology and the necessity to investigate right away their diffusion and, possibly, the role of additional factors other than Xfp in the general decline of olive groves in Apulia. Hence the importance of assessing the degree of overlap of BTD/Botryosphariaceae with OQDS/Xfp is discussed.

First report of seedling stem blight of mango caused by Neofusicoccum parvum in Italy

Seedling blight of mango (Mangifera indica L.) was observed in a commercial nursery located in Messina province (eastern Sicily, Italy) during winter of 2021. More than 30% of 3,000 seedlings, about three to six months old, of mango cv. Gomera 3 showed symptoms of basal stem blight. The symptoms started from seed, led to the decline and subsequent death of the plants. Necrotic lesions appeared at crown level two months after sowing. The stem tissues of ten symptomatic plants were cut, surface sterilized, dipped in 1.5% sodium hypochlorite for 1 min and transferred onto potato dextrose agar medium (PDA) and incubated at 25°C for four days. Approximately 60% of stem tissues developed very similar fungal colonies, resembling to Botryosphaeriaceae. A total of four representative isolates were collected through single hyphal-tip and stored at 4 °C. The internal transcriber spacer region (ITS) was amplified with primers, ITS5/ITS4 (White et al., 1990), and EF1-728F and EF1-986R (Carbone and Kohn, 1999) were used to amplify part of the translation elongation factor 1alpha gene (tef1-α), and primers Bt2a/Bt2b (Glass and Donaldson, 1995) were used for the partial β-tubulin (tub2). The obtained sequences were deposited in GenBank with accession numbers: ON911292-95 for the ITS, ON933621-24 for tef1-α and ON933625-28 for tub2.To compare the results, 50 additional sequences were selected and inserted in the alignment according to the recent literature on the Botryosphaeriaceae (Bezerra et al., 2021; Zhang et al., 2021). Maximum parsimony analysis (MP) of concatenated dataset (ITS + tef1-α + tub2) was performed in PAUP v.4.0a. Clade support was assessed by 1,000 bootstrap replicates and Botryosphaeria dothidea was used as an outgroup. Our isolates clustered within the group of Neofusicoccum parvum (71% bootstrap value) (ex-type CMW9081). Based on these results, and morphological data (50 conidia length × width average: 18.1 × 6.6, respectively) our isolates (named MC) were identified and confirmed as Neofusicoccum parvum (Pennycook & Samuels) Crous, Slippers & A.J.L. Phillips. Pathogenicity tests were also conducted on 18 mango cv. Gomera 3 seedlings. The crown roots of each seedling were mechanically wounded and a mycelial plug of the isolate MC14 was placed onto them and covered with soil. Controls (three seedlings) were inoculated with sterile PDA only. Seedlings were maintained in a growth chamber with a 12 hrs photoperiod at 25°C ± 1°C and watered regularly. After five days, stem lesions appeared externally (1.6 cm) and one month after the inoculation, all the inoculated seedlings died. However, controls did not show any obvious symptoms. Re-isolations were conducted as described above and fulfilled Koch's postulates confirming pathogenicity. Among the diseases affecting mango plants, Botryosphaeriaceae represent a serious threat in Sicily as reported by Aiello et al., 2022. The endophytic behaviour of Botryosphaeriaceae is well known, making them latent pathogens (Slippers and Wingfield, 2007). In Italy, N. parvum was detected in mango orchards since 2013 (Ismail et al. 2013), but symptoms of seedlings stem blight have never been reported in the nursery. In Sicily, an increase of Botryosphaeriaceae infection has been observed recently, especially in nurseries, where N. parvum has been identified as a most destructive pathogen (Aiello et al., 2020; Gusella et al., 2021). To our knowledge, this is the first report worldwide of N. parvum causing mango seedling blight. The high incidence of infected seedlings detected in this study highlights the potential risk during propagation in the nursery, representing a significant source of inoculum for the field.

First report of Diaporthe eres causing stem blight and dieback on highbush blueberry (Vaccinium corymbosum) in Italy

Vaccinium corymbosum L. is a woody deciduous shrub belonging to the Ericaceae family. During the last decade, Northern Italy has become a major area for blueberry cultivation and production in Europe, supplying other countries with high quality fruit (FAOSTAT 2020). In June 2020, plant stem and branch wilting with brownish necrotic internal lesions were observed on 20% of around 250 plants of the cultivar (cv.) Draper cultivated in a soilless culture system located in Peveragno (Piedmont, Cuneo Province, 44°21'05.6''N, 07°37'23.2''). Dieback and death of the plants also occurred. Fifteen symptomatic plants were collected. Wood pieces (5-10 mm) excised from diseased stems and branches were sterilized in 1% sodium hypochlorite for 1 min, rinsed in sterile distilled water and dried on sterile absorbent paper. Small fragments (2-3 mm), obtained from the edge of the necrotic tissues, were plated on potato dextrose agar (PDA) amended with 25 mg/L of streptomycin sulfate. Plates were incubated at 25 ± 1°C under a 12 h photoperiod and, five days after, colonies with the same characteristics of Diaporthe spp. were established from single hyphal tip transfers. Two representative strains (CVG1130 and CVG1131) were grown on PDA from single hyphal-tip transfers. After 7 days, white colonies with fluffy, aerial, mycelium reaching 8.3 cm were observed. colonies turned gray after three weeks producing dark brown pycnidia. Aseptate, hyaline, fusiform to ellipsoidal, measuring 6.3 to 8.4 × 2.2 to 3.0 μm alpha conidia were produced. No beta conidia were observed. The DNA of the same strains was extracted and a polymerase chain reaction (PCR) was performed for the ITS (primer set: ITS1-ITS4) (GenBank Accession no. ON834528; ON834529), tef (EF1-728/EF1-986) (GenBank Accession no. ON843715; ON843716) and tub2 (T1/Bt2b) (GenBank Accession no. ON843713; ON843714) regions, in accordance with previous studies (Gomes et al. 2013, Bezerra et al. 2021). Sequences analysed with BLASTn algorithm (Altschul et al. 1997) exhibited 98% identity with the ex-type strain CBS 138594 of Diaporthe eres for ITS (GenBank Accession no. KJ210529), 100% identity for tub2 (GenBank Accession no. KJ420799) and 99% identity for tef (GenBank Accession no. KJ210550). The maximum likelihood method based on combined sequences of ITS, tef and tub2 loci was performed, and the isolates CVG1130 and CVG1131 clustered with several reference strains of D. eres (Supplementary figure). To fulfil Koch's postulates, pathogenicity tests were performed on 1-year-old blueberry potted plants cv. Draper and Duke. A small piece of the bark tissue was removed with a sterile-bladed scalpel to expose the cambium. Mycelium plugs (5 mm diameter), obtained from 10-day-old cultures of the strains CVG1130 and CVG1131, were placed with the mycelium in contact with the internal plant tissues. Three plants were used for each isolate and the inoculation points were sealed with Parafilm®. The same number of plants treated with sterile PDA plugs were used as control. Plants were placed in a growth chamber at 25°C for 3 weeks. After this period, symptoms similar to those observed in the field appeared on the inoculated plants, while control plants remained healthy. A fungus with the same morphological characteristics of D. eres was reisolated from inoculated plants and identified by sequencing the tub2 gene to confirm Koch's postulates. Diaporthe eres was previously reported on different Vaccinium spp. in Chile, Lithuania, the Netherlands and the U.S.A. (Farr and Rossman, 2022). To our knowledge, this is the first report of D. eres associated with stem blight and dieback of highbush blueberry in Italy. Duke and Draper are among the most cultivated blueberry cultivars in Piedmont, where the spread of D. eres could represent a serious threat.

Diaporthe citri: A Fungal Pathogen Causing Melanose Disease

Citrus melanose is a fungal disease caused by Diaporthe citri F.A. Wolf. It is found in various citrus-growing locations across the world. The host range of D. citri is limited to plants of the Citrus genus. The most economically important hosts are Citrus reticulata (mandarin), C. sinensis (sweet orange), C. grandis or C. maxima (pumelo), and C. paradisi (grapefruit). In the life cycle of D. citri throughout the citrus growing season, pycnidia can be seen in abundance on dead branches, especially after rain, with conidia appearing as slimy masses discharged from the dead twigs. Raindrops can transmit conidia to leaves, twigs, and fruits, resulting in disease dispersion throughout small distances. Persistent rains and warm climatic conditions generally favor disease onset and development. The melanose disease causes a decline in fruit quality, which lowers the value of fruits during marketing and exportation. High rainfall areas should avoid planting susceptible varieties. In this article, information about the disease symptoms, history, geographic distribution, epidemiology, impact, and integrated management practices, as well as the pathogen morphology and identification, was reviewed and discussed.

Woody Canker and Shoot Blight Caused by Botryosphaeriaceae and Diaporthaceae on Mango and Litchi in Italy

In recent years, the cultivation of tropical fruit crops has increased in the Mediterranean basin, especially in southern Italy. In surveys conducted from 2014 to 2019 woody canker and shoot blight were observed on mango plants (cvs. Kent, Keitt, Sensation, Osteen, and Kensington Pride) and litchi plants (cvs. Way Chee and Kwai Mai Pink) cultivated in Sicily. Botryosphaeriaceae and Diaporthaceae were consistently isolated from symptomatic samples. Morphological characterization and multi-locus phylogenies using three genomic loci (a portion of translation elongation factor 1-α gene, a portion of the β-tubulin gene, and an internal transcribed spacer) identified these fungi as Neofusicoccum parvum, Lasiodiplodia theobromae, Botryosphaeria dothidea, Diaporthe foeniculina, and Diaporthe baccae on mango and Diaporthe foeniculina and Diaporthe rudis on litchi. Pathogenicity tests on healthy mango (cv. Kensington Pride) and litchi (cv. Way Chee) plants demonstrated the pathogenicity of the isolates used in the study, and Koch’s postulates were fulfilled for all pathogens. To our knowledge, this is the first report of L. theobromae, B. dothidea, and Diaporthe species on mango in Italy and the first report worldwide of woody canker and shoot blight caused by D. foeniculina and D. rudis on litchi plants.

A New Disease for Europe of Ficus microcarpa Caused by Botryosphaeriaceae Species

The Indian laurel-leaf fig (Ficus microcarpa) is an important ornamental tree widely distributed in the urban areas of Italy. Surveys conducted in 2019 and 2020 on several tree-lined streets, squares, and public parks in Catania and Siracusa provinces (Sicily, southern Italy) revealed the presence of a new disease on mature trees. About 9% of approximately 450 mature plants showed extensive branch cankers and dieback. Isolations from woody tissues obtained from ten symptomatic plants consistently yielded species belonging to the Botryosphaeriaceae family. The identification of the recovered fungal isolates was based on a multi-loci phylogenetic (maximum parsimony and maximum likelihood) approach of the ITS, tef1-α, and tub2 gene regions. The results of the analyses confirmed the presence of three species: Botryosphaeria dothidea, Neofusicoccum mediterraneum, and N. parvum. Pathogenicity tests were conducted on potted, healthy, 4-year-old trees using the mycelial plug technique. The inoculation experiments revealed that all the Botryosphaeriaceae species identified in this study were pathogenic to this host. Previous studies conducted in California showed similar disease caused by Botryosphaeriaceae spp., and the pathogenic role of these fungi was demonstrated. To our knowledge, this is the first report of Botryosphaeriaceae affecting Ficus microcarpa in Europe.

Management of Phytophthora parasitica causing gummosis in citrus using biogenic copper oxide nanoparticles

AIM

The main aim of the present study is to develop nanotechnology-based solutions for the management of a fungus, Phytophthora parasitica causing gummosis in citrus.

METHODS AND RESULTS

Biogenic copper nanoparticles (CuONPs) were synthesized using two different biocontrol agents, Pseudomonas fluorescens and Trichoderma viride and characterized using different analytical techniques. Further, in vitro (at the concentrations of 10 mg/L, 15 mg/L, 30 mg/L, 50 mg/L, 70 mg/L, 100 mg/L and 150 mg/L) and in vivo (at the concentration of 100 mg/L) activities of these nanoparticles were evaluated for their antifungal efficacy against P. parasitica. The results obtained confirmed the synthesis of irregular shaped CuONPs having a size in the range of 40-100 nm in case of P. fluorescens, whereas, spherical CuONPs in the size range of 20-80 were recorded in case of T. viride. As far as the in vitro antifungal efficacies of both these CuONPs is concerned, the maximum percent growth inhibition was observed in case of CuONPs synthesized from T. viride compared to CuONPs from P. fluorescens. However, in case of in vivo antifungal efficacies, CuONPs synthesized from T. viride showed the activity significantly higher than the conventionally used Bordeaux mixture.

CONCLUSIONS

It can be concluded that biosynthesized CuONPs can be effectively used as a potential fungicide against P. parasitica.

SIGNIFICANCE AND IMPACT OF THE STUDY

The application of nanoparticles having antifungal activities can be used as alternative fungicides to the conventional chemical fungicides. It has the potential to revolutionize the existing management strategies available for plant pathogenic fungi.

Neofusicoccum mediterraneum Is Involved in a Twig and Branch Dieback of Olive Trees Observed in Salento (Apulia, Italy)

Olive trees are infected and damaged by Botryosphaeriaceae fungi in various countries. The botryosphaeriaceous fungus Neofusicoccum mediterraneum is highly aggressive and is a major concern for olive groves in Spain and California (USA), where it causes 'branch and twig dieback' characterized by wood discoloration, bark canker, and canopy blight. During surveys of olive groves in Apulia (southern Italy), we noticed that-in some areas-trees were heavily affected by severe branch and twig dieback. In addition, chlorosis and the appearance of red-bronze patches on the leaf preceded the wilting of the foliage, with necrotic leaves persisting on the twigs. Given the severity of the manifestation in zones also subject to olive quick decline syndrome (OQDS) caused by Xylella fastidiosa subsp. pauca, we investigated the etiology and provide indications for differentiating the symptoms from OQDS. Isolation from diseased wood samples revealed a mycete, which was morphologically and molecularly identified as N. mediterraneum. The pathogenicity tests clearly showed that this fungus is able to cause the natural symptoms. Therefore, also considering the low number of tested samples, N. mediterraneum is a potential causal agent of the observed disease. Specifically, inoculation of the twigs caused complete wilting in two to three weeks, while inoculation at the base of the stem caused severe girdling wedge-shaped cankers. The growth rate of the fungus in in vitro tests was progressively higher from 10 to 30 °C, failing to grow at higher temperatures, but keeping its viability even after prolonged exposure at 50 °C. The capacity of the isolate to produce catenulate chlamydospores, which is novel for the species, highlights the possibility of a new morphological strain within N. mediterraneum. Further investigations are ongoing to verify whether additional fungal species are involved in this symptomatology.

Bot Gummosis of Lemon (Citrus × limon) Caused by Neofusicoccum parvum

Neofusicoccum parvum, in the family Botryosphaeriaceae, was identified as the causal agent of bot gummosis of lemon (Citrus × limon) trees, in the two major lemon-producing regions in Italy. Gummy cankers on trunk and scaffold branches of mature trees were the most typical disease symptoms. Neofusicoccum parvum was the sole fungus constantly and consistently isolated from the canker bark of symptomatic lemon trees. It was identified on the basis of morphological characters and the phylogenetic analysis of three loci, i.e., the internal transcribed spacer of nuclear ribosomal DNA (ITS) as well as the translation elongation factor 1-alpha (TEF1) and β-tubulin (TUB2) genes. The pathogenicity of N. parvum was demonstrated by wound inoculating two lemon cultivars, 'Femminello 2kr' and 'Monachello', as well as citrange (C. sinensis × Poncirus trifoliata) 'Carrizo' rootstock. In artificial inoculations, the fungus was very aggressive on lemons and weakly virulent on citrange, consistently with symptoms observed in the field as a consequence of natural infections. This is the first report of N. parvum, both in a wide and in a strict taxonomic sense, as a pathogen of lemon in Italy.