Phytopathology最新文献

Most Ralstonia solanacearum species complex strains cause bacterial wilts in tropical or subtropical zones, but the group known as race 3 biovar 2 (R3bv2) is cool virulent and causes potato brown rot at lower temperatures. R3bv2 has invaded potato-growing regions around the world but is not established in the United States. Phylogenetically, R3bv2 corresponds to a subset of the R. solanacearum phylotype IIB clade, but little is known about the distribution of the cool virulence phenotype within phylotype IIB. Therefore, genomes of 76 potentially cool virulent phylotype IIB strains and 30 public genomes were phylogenetically analyzed. A single clonal lineage within the sequevar 1 subclade of phylotype IIB that originated in South America has caused nearly all brown rot outbreaks worldwide. To correlate genotypes with relevant phenotypes, we quantified virulence of 10 Ralstonia strains on tomato and potato at both 22 and 28°C. Cool virulence on tomato did not predict cool virulence on potato. We found that cool virulence is a quantitative trait. Strains in the sequevar 1 pandemic clonal lineage caused the most disease, whereas other R3bv2 strains were only moderately cool virulent. However, some non-R3bv2 strains were highly cool virulent and aggressively colonized potato tubers. Thus, cool virulence is not consistently correlated with strains historically classified as the R3bv2 group. To aid in the detection of sequevar 1 strains, this group was genomically delimited in the LINbase web server, and a sequevar 1 diagnostic primer pair was developed and validated. We discuss implications of these results for the R3bv2 definition.

Verticillium dahliae is a soilborne phytopathogenic fungus causing Verticillium wilt on hundreds of plant species. Several sequenced genomes of V. dahliae are available, but functional characterization of most genes has just begun. Based on our previous comparison of the transcriptome from the wild-type and ΔVdCf2 strains, a significant upregulation of the gene cassette, Vd276-280, in the ΔVdCf2 strain was observed. In this study, the functional characterization of the Vd276-280 gene cassette was performed. Agrobacterium-mediated knockout of this gene cassette in V. dahliae significantly inhibited conidiation, melanized microsclerotium formation in the mutant strains, and their virulence toward cotton. Furthermore, deletion of individual genes in the Vd276-280 gene cassette identified that the disruption of VDAG_07276 and VDAG_07280 delayed microsclerotium formation, inhibited conidiation, and reduced virulence toward cotton. Our data suggest that VDAG_07276 and VDAG_07280 in the Vd276-280 gene cassette mainly act as positive regulators of development and virulence in V. dahliae.

In soilborne diseases, the plant-pathogen interaction begins as soon as the seed germinates and develops into a seedling. Aphanomyces euteiches, an oomycete, stays dormant in soil and is activated by sensing the host through chemical signals present in the root exudates. The composition of plant exudates may, thus, play an important role during the early phase of infection. To better understand the role of root exudates in plant resistance, we investigated the interaction between partially resistant lines (PI660736 and PI557500) and susceptible pea cultivars (CDC Meadow and AAC Chrome) against A. euteiches during the pre-invasion phase. The root exudates of the two sets of cultivars clearly differed from each other in inducing oospore germination. PI557500 root exudate not only had diminished induction but also inhibited the oospore germination. The contrast between the root exudates of resistant and susceptible cultivars was reflected in their metabolic profiles. Data from fractionation and oospore germination inhibitory experiments identified a group of saponins that accumulated differentially in susceptible and resistant cultivars. We detected 56 saponins and quantified 44 of them in pea root and 30 from root exudate; the majority of them, especially soyasaponin I and dehydrosoyasaponin I with potent in vitro inhibitory activities, were present in significantly higher amounts in both roots and root exudates of PI660736 and PI557500 compared with Meadow and Chrome. Our results provide evidence for saponins as deterrents against A. euteiches, which might have contributed to the resistance against root rot in the studied pea cultivars. [Formula: see text] Copyright © 2024 His Majesty the King in Right of Canada, as represented by the Minister of Agriculture and Agri-Food Canada and the National Research Council of Canada. This is an open access article distributed under the CC BY 4.0 International license.

In recent years, the bacterium Xylella fastidiosa has been spreading in almond orchards (causing almond leaf scorch) and in grapevines (causing Pierce's disease) in northern Israel. Sucking insects specialized for xylem sap-feeding transmit this plant pathogen, but the identity of the vector(s) in Israel has not been determined. Hence, we sought to determine the main potential vector(s) of X. fastidiosa in Israel. In our surveys in northern Israel, we collected and identified four species of spittlebugs: Neophilaenus campestris, Philaenus arslani, Cercopis intermedia, and Mesoptyelus impictifrons. The first two species were found in very low numbers. C. intermedia was found only in spring and did not transmit X. fastidiosa in controlled experiments. M. impictifrons was the most abundant and widely distributed species in our survey and was found in and around infected vineyards in northern Israel. In controlled experiments, we found that 35 to 39% of M. impictifrons adults acquire X. fastidiosa from infected vines and almonds and subsequently transmit it to vines and almonds. Taken together, this study suggests that M. impictifrons is an important new vector of X. fastidiosa in almond orchards and vineyards in northern Israel. Further studies are needed on M. impictifrons' biology, ecology, and role as a vector of X. fastidiosa.

Rice production worldwide is threatened by the disease bacterial panicle blight (BPB) caused by Burkholderia glumae. Despite the threat, resources to control this disease, such as completely resistant cultivars or effective chemical methods, are still lacking. However, the need to control this disease has paved the way to explore biologically based approaches harnessing the antimicrobial activities of environmental bacteria. Previously, the bacterium Pseudomonas protegens PBL3 was identified as a potential biological control agent against B. glumae due to its antimicrobial activity against B. glumae. Such antimicrobial activity in vitro and in planta was associated with the P. protegens PBL3 bacteria-free secreted fraction (secretome), although the specific molecules responsible for this activity have remained elusive. In this work, we advance the characterization of the P. protegens PBL3 secretome by evaluating the antimicrobial activity in vitro of selected secondary metabolites predicted by the P. protegens PBL3 genomic sequence against B. glumae. In addition, using reversed-phase liquid chromatography tandem mass spectrometry of the P. protegens PBL3 secretome enabled us to successfully detect and quantify pyoluteorin, 2,4-diacetylphloroglucinol, and pyochelin. Among those, pyoluteorin and 2,4-diacetylphloroglucinol reduced the growth of B. glumae in vitro, along with reducing the symptoms of BPB and bacterial growth in planta, suggesting that these compounds could be effective as biopesticides to mitigate BPB.

Grapevine downy mildew (GDM), caused by the oomycete Plasmopara viticola, can cause 100% yield loss and vine death under conducive conditions. High-resolution multispectral satellite platforms offer the opportunity to track rapidly spreading diseases such as GDM over large, heterogeneous fields. Here, we investigated the capacity of PlanetScope (3 m) and SkySat (50 cm) imagery for season-long GDM detection and surveillance. A team of trained scouts rated GDM severity and incidence at a research vineyard in Geneva, New York, from June to August 2020, 2021, and 2022. Satellite imagery acquired within 72 h of scouting was processed to extract single-band reflectance and vegetation indices (VIs). Random forest models trained on spectral bands and VIs from both image datasets could classify areas of high and low GDM incidence and severity with maximum accuracies of 0.85 (SkySat) and 0.92 (PlanetScope). However, we did not observe significant differences between VIs of high and low damage classes until late July to early August. We identified cloud cover, image co-registration, and low spectral resolution as key challenges to operationalizing satellite-based GDM surveillance. This work establishes the capacity of spaceborne multispectral sensors to detect late-stage GDM and outlines steps toward incorporating satellite remote sensing in grapevine disease surveillance systems. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

In several plant species, thiamin foliar application primes plant immunity and can be effective in controlling various diseases. However, the effectiveness of thiamin against potato pathogens has seldom been investigated. Additionally, the transcriptomics and metabolomics of immune priming by thiamin have not previously been investigated. Here, we tested the effect of thiamin application against Alternaria solani, the causal agent of early blight in potato, and identified associated changes in gene expression and metabolite content. Thiamin applied on foliage at an optimal concentration of 10 mM reduced lesion size by ~33%. However, prevention of lesion growth was temporally limited, as a reduction of lesion size occurred when leaves were inoculated 4 h, but not 24 h, following thiamin treatment. Additionally, the effect of thiamin on lesion size was restricted to the application site and was not systemic. RNA-seq analysis showed that thiamin affected the expression of 308 genes involved in the synthesis of salicylic acid, secondary metabolites, fatty acid, chitin, and primary metabolism, and photosynthesis, which were also amongst the thousands of genes differentially regulated in the response to pathogen alone. Several of these genes and pathways were more differentially expressed and enriched when thiamin and the pathogen were combined. Thiamin also delayed the downregulation of photosynthesis-associated genes in plants inoculated with A. solani. Metabolite analyses revealed that thiamin treatment in the absence of pathogen decreased the amounts of several organic compounds involved in the citric acid cycle. We hypothesize that thiamin primes plant defenses through perturbation of primary metabolism.

Charcoal rot, caused by the soilborne fungus Macrophomina phaseolina (Mp) poses a serious threat to soybean health and harvests at a global scale. Mp exhibits varying distribution patterns across fields, which complicates our ability to predict disease occurrences and outbreaks. Therefore, determining the spatial distribution of Mp abundance and its relation with soil physicochemical properties would help to inform precision management decisions for mitigating charcoal rot. To achieve this, Mp colony forming units (CFU) and edaphic properties were evaluated in 297 soybean fields located in the main soybean growing regions across 7 Departments of Paraguay. A pattern of decreasing CFU density was observed from the south-eastern to the western part of the country. While several edaphic factors are positively correlated with Mp CFU, pH showed a significant negative correlation with CFU. Both spatial and non-spatial model suggest that cation exchange capacity, percentage of clay, and pH could be potential predictors of Mp CFU abundance. Including spatial dependence of edaphic factors improved the prediction of Mp CFU more effectively than classical statistical models. We demonstrated that the occurrence of Mp shows a significant spatial clustering pattern as indicated by Moran's I. Our findings will help growers and policy-makers make informed decisions for managing Mp by improving our ability to predict which agricultural fields and soils are at greatest risk for charcoal rot.

Clubroot disease caused by the biotrophic pathogen Plasmodiophora brassicae, is one of the most serious threats to cruciferous crops production worldwide. P. brassicae is known for rapid adaptive evolution to overcome resistance in varieties. It is urgent to establish alternative management to control P. brassicae. In this study, we identified two P. brassicae secretory proteins that were up-regulated during infection and effected plant defense. We established a method for transient expression in the roots of seedlings and demonstrated that P. brassicae could take up substances from the environment of root cells. Using a RNA interference (RNAi)-based host-induced gene silencing (HIGS) by expression of hairpin RNAi constructs with sequence homology to P. brassicae effector Pb48 or Pb52 in susceptible Brassica rapa plants enhanced host disease resistance. After silencing these two effectors, the transcription levels of cytokinin biosynthesis gene IPT1 and the regulation gene of auxin homeostasis GH3.5 were down-regulated. These results suggested that RNAi-based HIGS of effectors has a great practical application of improving crop resistance against P. brassicae and can contribute to environmentally sustainable agriculture.

The development of novel improved varieties adapted to unstable environmental conditions is possible through the genetic diversity of breeding materials. Potato is among the most important food crops worldwide, however, there are still significant hindrances to breeding gains attributed to its autotetraploid and highly heterozygous genome. Bacterial wilt caused by the Ralstonia solanacearum species complex (RSSC) is an important disease affecting potato among many economically important crops worldwide. No cultivated potato genotypes have shown a satisfactory level of resistance to bacterial wilt. Nevertheless, resistance can play a crucial role in effective integrated disease management. To understand the genetic landscape of bacterial wilt resistance in cultivated potato, we evaluated the diversity of 194 accessions from the International Potato Centre (CIP) using 9,250 single nucleotide polymorphisms (SNPs) and their associations to the response to bacterial wilt disease evaluated over two independent trials. Twenty-four accessions showed high resistance throughout both trials. Genetic diversity analysis revealed three major clusters whose subgroups were mostly represented by CIP clones derived from common parents. Genome-wide association analyses have shown six major hits: two on chromosome 8, and one on each chromosome 2, 4, 5, and 9. These results facilitate genetic dissection of bacterial wilt resistance and marker-enabled breeding in elite genotypes for potato breeding initiatives.