Plant disease最新文献

Powdery mildew, caused by the fungus Erysiphe necator, is one of the primary causes of grape yield loss across the globe. While numerous resistance loci have been identified in various grapevine species, the genetic determinants of susceptibility to E. necator remain largely unexplored. Understanding the genetics of susceptibility for pathogenesis is equally important for developing durable resistance grapevines against this pathogen. To identify these factors in Vitis interspecific hybrid 'Chambourcin', a controlled leaf disc assay was conducted for two years using an automated microscopy phenotyping system with 273 F1 genotypes from a cross of 'Chambourcin' and V. vinifera 'Cabernet Sauvignon'. Additionally, a high-resolution linkage map using the same number of 'Chambourcin'-derived hybrids was constructed with 355 simple sequence repeats (SSR) and 1,394 RNaseH2-dependent amplicon sequencing (rhAmpSeq)-derived haplotype markers that clustered into 19 linkage groups. A quantitative trait locus (QTL) analysis identified a susceptibility locus (here named Sen2) on linkage group (LG) 7 explaining 8.90 % - 12.57 % of the total phenotypic variance. The markers associated with this susceptibility locus were used to identify 78 accessions in the USDA-ARS cold hardy Vitis collection at Geneva, NY that carry Sen2 and can be used to selectively exclude susceptible progenies. Additionally, 6 accessions carry the alternative haplotype encoding recessive resistance and can be used for resistance breeding. The identification of powdery mildew susceptibility loci is crucial for identifying genes that could be targeted for gene knock-out, gene editing, RNA interference (RNAi), or selection among breeding genotypes to enhance sustainable protection against pathogens.

Kiwifruit Vine Decline Syndrome (KVDS) is a soilborne disease affecting Actinidia fruit trees in perennial cropping systems. Since its emergence in 2012, studies have increasingly identified the oomycete Phytopythium vexans as a major causative agent of the disease. P. vexans is also implicated in complex soilborne disease systems of woody perennial crops, including replant disease in apple and pear. To date, most molecular assays for the detection of P. vexans target the nuclear ribosomal internal transcribed spacer (ITS), a region which is ill-suited for distinguishing between closely related oomycete species. The cytochrome oxidase subunit I (COI) mitochondrial gene was targeted for the design of new primers because it was previously identified as a better marker for differentiating oomycete species. The FOR2/REV4RCA primer pair gave the best results regarding PCR specificity and was selected for use in a SYBR Green-based qPCR assay. The specificity of the qPCR assay was evaluated using 29 P. vexans strains (including different phylogenetic groups) as well as a wide variety of closely related off-target species associated with pathogenic soil communities of fruit trees. P. vexans strains were successfully quantified down to 20 fg in water and in DNA extracted from kiwifruit roots. P. vexans was also detected in artificially inoculated Actinidia plant roots as well as in a variety of naturally infected field samples of both kiwi and apple trees. These results suggest that the qPCR assay developed in this study is highly sensitive and specific to target pathogen, regardless of sample matrix.

Sugar beet roots in Idaho are held under ambient conditions in outdoor storage piles which can lead to fungal growth and rot and substantial sucrose loss. Thus the incidence, distribution, and pathogenicity of fungi associated with fungal growth on the surface of sugar beet roots on top of outdoor piles was investigated. The surface fungal growth on sugar beet roots held on top of 14 Idaho outdoor piles [tarped ventilated (TV) piles and piles with no tarps or ventilation (NTV) at 7 locations] was assessed in 2018-19 and 2019-20. Cladosporium spp. were the only fungi covering more than 1% of the root surface (2 to 48%) on top of NTV piles both years with the most frequently isolated species being C. cladosporioides, C. macrocarpon, and C. subtilissimum both years. On TV piles Cladosporium spp. (13 to 60%) were also dominant, but Penicillium spp. (0 to 35%), an Athelia-like basidiomycete (0 to 2%), and Botrytis cinerea (0 to 2%) were also frequently present. In the plug assay to test pathogenicity, B. cinerea caused the most rot (P < 0.0001; averaged 31 to 32 mm of rot) followed by Penicillium spp. (P. expansum 14-22 mm, P. polonicum 14-16 mm, and P. cellarum 10 mm). Although Cladosporium spp. caused little or no rot (0 to 2 mm), workers should be cautious on or around sugar beet piles since a number of the Cladosporium spp. are established to be associated with human clinical samples.

Howler EVO is a biological fungicide based on metabolites of the bacterium Pseudomonas chlororaphis strain AFS009. One of the metabolites, pyrrolnitrin (PRN), is a chemical analogue of the phenylpyrrole fludioxonil used to manage gray mold of fruit crops caused by Botrytis cinerea. Resistance to fludioxonil in B. cinerea is well documented and linked to mutations in the transcription factor mrr1, leading to overexpression of the ATP-Binding Cassette (ABC) transporter gene BcatrB. Moderately resistant isolates are designated MDR1 and MRD1h based on the specific variation of mutations in mrr1 and the level of BcatrB expression. This study investigated EC50 values of 54 B. cinerea isolates sensitive and with moderate resistance to fludioxonil for sensitivity to fludioxonil and Howler EVO. The Pearson correlation coefficient indicated a strong correlation between EC50 values of fludioxonil and Howler EVO. Isolates that were moderately resistant to fludioxonil and classified as MDR strains were also moderately resistant to Howler EVO. The effect of Howler EVO and fludioxonil on BcatrB gene expression was studied by qPCR. Both fungicides induced the BcatrB gene expression significantly up to 100-fold in sensitive B. cinerea isolates. Howler EVO significantly induced the BcatrB gene expression in all MDR1 isolate but not in the MDR1h isolate. In detached fruit assays on cherry, sensitive B. cinerea isolates were completely inhibited by formulated fludioxonil (Scholar) and significantly suppressed in growth by Howler EVO. However, MDR1 and MDR1h isolates produced disease in Scholar and Howler EVO treatments. Our results indicate cross-resistance between the synthetic fungicide fludioxonil and the biofungicide Howler EVO, indicating that, at least for some biofungicides, resistance management is necessary.