Search

English walnut (Juglans regia) has become an important crop in Chile, representing 11.5% of the total area of fruit trees, surpassed only by grapevine. As the Chilean walnut industry rapidly expands, young orchards are at risk from the emergence of new fungal diseases. Botryosphaeriaceae and Diaporthaceae fungi have been recognized as main causes of wood diseases in walnut, with symptoms of dieback, canker, and blight. In winter 2017, samples were collected from different orchards in Valparaíso and Maule regions. Fungal isolates recovered were cultured, characterized morphologically, and identified using DNA sequence analyses. Three species (Neofusicoccum parvum, Diplodia mutila, Diplodia seriata) were characterized in Botryosphaeriaceae and two (Diaporthe cynaroidis, Diaporthe australafricana) in Diaporthaceae. Pathogenicity tests showed that N. parvum was the most aggressive species to walnut. This study confirmed the presence of pathogenic Botryosphaeriaceae and Diaporthaceae in J. regia that should be considered an increasing risk for the growing Chilean walnut industry. [ABSTRACT FROM AUTHOR]

Botryosphaeria dieback is one of the most prevalent grapevine trunk diseases (GTDs), and is caused by fungi in the Botryosphaeriaceae. Fungi invade grapevine vascular systems mainly through pruning wounds, and cause cankers and necrotic lesions, which lead to grapevine decline and death. Lasiodiplodia theobromae has been reported as a highly virulent pathogen of grapevine, and was previously reported in Mexican vineyards. The taxonomy of Lasiodiplodia was recently revised, adding new species, and some were reduced to synonymy. This study aimed to characterize Lasiodiplodia producing grapevine dieback symptoms in Sonora and Baja California, Mexico. Using the phylogenetic markers tef1-a and ITS regions, Lasiodiplodia brasiliensis, L. crassispora, L. exigua, and L. gilanensis were identified. Lasidiplodia exigua was the most prevalent species. Lasiodiplodia brasiliensis and L. gilanensis were very virulent to 'Cabernet Sauvignon' plants, while L. exigua and L. gilanensis were less virulent, and L. crassispora did not produce lesions at 2 months post-inoculation. The optimum temperature of the Lasiodiplodia spp. was 28°C, but all four species grew up to 37°C, and the isolates of L. exigua grew slowly at 40°C. This is the first report of the four of Lasiodiplodia species in vineyards of Mexico. [ABSTRACT FROM AUTHOR]

The Botryosphaeriaceae is a fungal family that includes many destructive vascular pathogens of woody plants (e.g., Botryosphaeria dieback of grape, Panicle blight of pistachio). Species in the genera Botryosphaeria , Diplodia , Dothiorella , Lasiodiplodia , Neofusicoccum , and Neoscytalidium attack a range of horticultural crops, but they vary in virulence and their abilities to infect their hosts via different infection courts (flowers, green shoots, woody twigs). Isolates of seventeen species, originating from symptomatic apricot, grape, pistachio, and walnut were tested for pathogenicity on grapevine wood after 4 months of incubation in potted plants in the greenhouse. Results revealed significant variation in virulence in terms of the length of the internal wood lesions caused by these seventeen species. Phylogenomic comparisons of the seventeen species of wood-colonizing fungi revealed clade-specific expansion of gene families representing putative virulence factors involved in toxin production and mobilization, wood degradation, and nutrient uptake. Statistical analyses of the evolution of the size of gene families revealed expansions of secondary metabolism and transporter gene families in Lasiodiplodia and of secreted cell wall degrading enzymes (CAZymes) in Botryosphaeria and Neofusicoccum genomes. In contrast, Diplodia , Dothiorella , and Neoscytalidium generally showed a contraction in the number of members of these gene families. Overall, species with expansions of gene families, such as secreted CAZymes, secondary metabolism, and transporters, were the most virulent (i.e., were associated with the largest lesions), based on our pathogenicity tests and published reports. This study represents the first comparative phylogenomic investigation into the evolution of possible virulence factors from diverse, cosmopolitan members of the Botryosphaeriaceae. [ABSTRACT FROM AUTHOR]

Trunk diseases are factors that limit sustainability of vineyards worldwide. Botryosphaeria and Eutypa diebacks are caused by several fungi belonging to the Botryosphaeriaceae and Diatrypaceae, respectively, with Diplodia seriata and Eutypa lata being two of the most common species. Previous information indicated that the traditional isolation method used to detect these pathogens from plant samples could underestimate their incidence levels. In the present study, we designed two sets of primers that target the β-tubulin gene and that are amenable for quantitative real-time PCR (qPCR) Sybr-Green assays for the detection and quantification of D. seriata-complex (DseCQF/R) and E. lata (ElQF/R) DNA. The design of a species-specific assay was achieved for E. lata. For D. seriata, a species-specific assay could not be designed. The low interspecific diversity across β-tubulin genes resulted in an assay that could not discriminate D. seriata from some closely related species either not yet reported or presenting a low prevalence on grapevine, such as D. intermedia. We validated our technique on grapevine spur samples naturally and artificially infected with D. seriata and E. lata during the dormant season. Experimental grapevines were located in two counties of northern California where the incidence of both pathogens was previously reported. The qPCR assays revealed that a high frequency of pruning wound infections (65%) was achieved naturally by E. lata, while low infection frequency (less than 5%) was observed using the reisolation method. For D. seriata-complex, low (5%) to no natural infection frequencies were observed by the qPCR and the reisolation method, respectively. These results also provided evidence that our qPCR detection methods were more sensitive to assess the incidence of E. lata and D. seriata-complex in plant samples, than traditional isolation techniques. Benefits of molecular methods for the detection of canker pathogens in the field under natural conditions are discussed. [ABSTRACT FROM AUTHOR]