Plant disease最新文献

Pea streak virus (PeSV) is an aphid-transmitted virus infecting a broad range of legumes, including alfalfa and cool season food legumes such as chickpeas, lentils, and peas. The diseases caused by PeSV in cool season food legumes were studied in the Pacific Northwest (PNW) of the U.S. in the past, prior to the availability of molecular tools and currently the genetic diversity of PeSV in the PNW is largely unknown. To fill in this knowledge gap and evaluate risks posed by main genetic variants of PeSV circulating in the PNW pulses, an isolate of PeSV was collected from alfalfa in Idaho and subjected to molecular and biological characterization on several major cool-season food legume species grown in the PNW, including chickpeas, lentils, and peas. This Idaho isolate of PeSV, PeSV-Id, induced severe necrotic symptoms in chickpeas, lentils, and dry peas, with a mortality reaching 100% in some chickpea lines. The virus was purified and used as an antigen for production of PeSV-specific antibodies, and development of a sensitive ELISA assay. Phylogenetically, PeSV-Id belonged to a tight lineage of North American isolates of the virus, distinct from the alfalfa latent virus strain of PeSV. The virus was easily transmitted mechanically under greenhouse conditions and was found to spread quickly in alfalfa in the field in the span of 3 to 52 months post-planting. Based on the data obtained, PeSV should be considered a potential threat to the production of pulse crops growing in the vicinity of alfalfa.

Red crown rot (RCR) of soybean, caused by Calonectria ilicicola, is new to the Midwest region of the United States, first identified in 2018 in western Illinois, and later in the neighboring states of Kentucky (2021), Indiana (2022) and Missouri (2024). Illinois has seen the most reported cases-various fields in 34 counties as of the end of the 2024 growing season. To determine the diversity and spread of C. ilicicola in Illinois, RCR-symptomatic soybean plants were collected across 44 fields from 18 Illinois counties and 79 C. ilicicola isolates were purified from lower stems. To examine the genetic diversity of these isolates, seven genetic regions were targeted for PCR amplicon sequence comparisons. The DNA sequences of the amplicons from act, cmdA, his3, tef1 and tub2 were identical to all. However, the ITS and IGS amplicons each revealed one single nucleotide polymorphism (SNP). Additionally, the PCR amplicon sequences were compared to amplicons from historical isolates collected between 1970 and 1988 in the Southeastern United States from peanut, blueberry, and soybean hosts. Sequence polymorphisms were found for all PCR amplicons (except cmdA) from the Southeastern U.S. isolates compared to the Illinois isolates, and these amplicon sequences were identical in all Southeastern U.S. isolates regardless of collection location or year. These results show that Illinois isolates collected from 2018 to 2024 showed low diversity and are most likely not due to the spread of the isolate(s) previously found in the Southeastern U.S.

The United States plays a significant role in fulfilling global soybean demand. Recent weather and changing management practices have increased oomycete-induced diseases in soybean fields in the U.S. and, more specifically, in Wisconsin. This study aimed to assess the oomycete diversity and abundance in soybean-growing regions in Wisconsin, characterize the pathotypes of Phytophthora sojae, and compare them to the soybean Rps genes historically deployed in Wisconsin's commercial cultivars. Over two years, 274 soil samples from 39 counties were successfully baited for oomycetes using a soybean leaf disc assay. In total, 388 isolates were identified from four oomycete genera. Overall, Globisporangium was the most abundant genus detected. Although a low diversity was observed in the samples, a high diversity was observed across counties, likely influenced by their geographic locations and the years sampled. While P. sojae was isolated at low frequency, the hypocotyl pathotyping assay identified two pathotypes with alleles 1a, 1b, 1c, 1k, and 3b. Analysis of the deployed Rps genes in variety trials in Wisconsin from 2015 to 2024 indicated a high frequency of the Rps1c and Rps1k genes in commercial cultivars. The pathotypes detected in this study suggest that the deployment of these genes is no longer effective, so the use of cultivars with the Rps3a gene is highly recommended. The insights regarding the oomycete population diversity and abundance in the state will enable the deployment of targeted disease management, addressing yield reductions caused by pathogenic oomycete species.

New lines of safflower, genetically modified to contain oleic acid above 90% in their oil, have been developed in Australia. The 2022 safflower-growing season in Western Australia was affected by many outbreaks of disease in the crop. Pathogens were isolated from disease-affected tissues from 15 different sites and identified using Sanger sequencing regions of the glyceraldehyde 3-phosphate dehydrogenase (Gapdh) and translation elongation factor 1-α (Tef1) genes. The predominant pathogens identified came from the genera Alternaria and Stemphylium, but did not include the known safflower pathogen Alternaria carthami (section Porri). Koch's postulates tests showed conclusively that Alternaria sect. Alternaria and Stemphylium eturmiunum were causal agents of disease, but tests on other fungal field isolates were inconclusive. The two causal agents confirmed through Koch's postulates were also the only ones found in grain samples that were tested for fungal contamination and could thus represent a possible source of infection.

Rhizoctonia solani is a soil- and seed-borne fungus, manifesting as black scurf and stem canker disease, resulting in substantial yield and quality losses globally. This fungus reproduces asexually through hyphae and sclerotia. Its genetic diversity is organized into 14 anastomosis groups (AGs), with AG3-PT being the predominant group on potato. Global trade of seed potatoes, though vital for agricultural development, inadvertently transmits the pathogen across regions. Disease development is influenced by environmental and agronomic factors, leading to severe outbreaks and economic impact. Accurate diagnosis is challenging due to the pathogen's genetic complexity, necessitating a transition from traditional culture-based and biochemical methods to molecular, genomic, and emerging digital technologies. Methods such as PCR, isothermal amplification, sequencing, sensor-based biosensing, and AI-driven imaging have improved the detection, quantification, and non-invasive monitoring of the pathogen. Combining these diagnostic methods into a tiered framework provides prospects for efficient disease surveillance, informed management decisions, and sustainable potato production systems.

Pomegranate is a high value crop severely affected by diseases caused by bacteria, viruses and fungi, especially those caused by Alternaria alternata. This pathogen is responsible for two major diseases black heart rot and black spot disease. Heart rot begins as a latent infection in the flower stigma, leading to internal aril necrosis, whereas black spot manifests as external necrotic lesions. While this review focuses on Alternaria diseases, it differentiates these symptoms from distinct internal rots caused by other fungi like Colletotrichum spp. and Fusarium spp. and surface lesions caused by Pseuodocercospora spp. and Curvularia spp. We examined current knowledge on Alternaria epidemiology, and the influence of physiological factors like fruit pH and calcium on susceptibility. Disease control remains challenging due to limited fungicides and pathogen latency, some promising solutions include biological control with Bacillus species, antifungal extracts, and detection via X-ray and AI-based imaging. Ultimately, a deeper understanding of these diseases and improvement of management strategies is essential to sustain global pomegranate yield and quality.

Pseudomonas coronafaciens pv. coronafaciens (Pcc), the causal agent of Bacterial Halo blight (BHB) on oat, has been infrequently reported in the United States, with historical records limited to the 1920s through the 1960s. In 2023, oat trial fields in Aberdeen, Idaho were severely infected with an unknown disease that formed necrotic lesions on leaves. Preliminary identification based on colony morphology suggested a pathogen belonging to the genus Pseudomonas. Subsequent polymerase chain reaction amplified a 298 bp fragment that is diagnostic to Pcc. Further analysis using whole-genome sequencing confirmed 99.6% average nucleotide identity (ANI) with Pcc. This marks the first detection of Pcc in Idaho, and the first detailed description of the pathogen in the United States after over half a century. Host range and pathogenicity assessments on multiple cereal crops showed that Pcc was pathogenic on oat, barley, and corn. However, wheat, rye and triticale displayed chlorosis and early cell death in response to the pathogen. Evaluation of oat and barley genotypes revealed resistance in the two crop species to be rare with only 2.5, and 4.5% of oat and barley genotypes exhibiting some level of resistance. Notably, the four resistant and moderately resistant barley genotypes identified in this study: DH170472, Celebration, Legacy and Quest are the first to be reported as sources of resistance to BHB. Results of the present study provide a basis for further research toward a better understanding of disease epidemiology, the genetics of host-pathogen interaction and the management of BHB on oat, barley and corn.

Ralstonia pseudosolanacearum is a soil-borne bacterial pathogen responsible for bacterial wilt disease in a wide range of host plants, including solanaceous crops. In this study, we collected 22 bacterial wilt isolates from solanaceous crops in seven sampling plots across the Kongo Central region of the Democratic Republic of Congo (DRC). The genomic characterization of these isolates identified a single haplotype belonging to the R. pseudosolanacearum phylotype I sequevar 31 genetic lineage. We assembled the genome sequence of one representative strain RUN6904, placed it in a phylogenetic context, and identified its type III effector repertoire. We demonstrated the virulence of the DRC isolates on tomato and showed the resistance of the AG91-25 eggplant accession likely triggered by the recognition of the RipAX2 type III effector from these isolates.

Xylella fastidiosa is a xylem-limited plant-pathogenic bacterium responsible for several economically significant plant diseases, including Pierce's disease in grapevine. Current control strategies face significant challenges in completely eradicating this pathogen. As such, phage-based biocontrol has gained increasing interest as a biocontrol tool in crop management. In this study, we expand current knowledge on X. fastidiosa phage diversity by reporting the isolation and characterization of 35 novel phages (ViSe_1 to ViSe_35) capable of infecting European X. fastidiosa subsp. fastidiosa strains. These phages were isolated from sewage samples using a collection of Xanthomonas spp. and X. fastidiosa strains as primary hosts. Phylogenetic analysis revealed a substantial genomic diversity, with phages being taxonomically classified in five distinct families: Schitoviridae, Mesyanzhinovviridae, Casjensviridae, Autographiviridae and Tectiviridae. Genomic analysis supports the proposal of four novel new genera and nine new species. Both highly specific and polyvalent phages were recovered, mostly depending on the isolation technique. All phages were able to infect strains from X. fastidiosa subsp. fastidiosa ST1, with fifteen of them consistently and completely inhibiting bacterial growth. Notably, none of the phages harbored genes associated with lysogeny, virulence or antibiotic resistance, suggesting a lytic life cycle and reinforcing their potential as biocontrol agents.

Anthracnose, caused by Colletotrichum spp., is an important fungal disease prevalent in strawberry nurseries and fruit production. Paenibacillus polymyxa, a plant growth-promoting rhizobacterium, effectively inhibits various fungal pathogens and their associated diseases. In this study, a fusaricidin synthetase gene (fusA)-disrupted mutant generated from a strawberry strain TP3 of Paenibacillus polymyxa was used to demonstrate the requirement of fusA for disease suppression directed by this beneficial bacterium. In contrast to the wild-type strain TP3, this fusA-disrupted mutant was unable to produce fusaricidins, but increased biofilm biomass; however, it reduced the inhibition of fungal growth and decreased the suppression of anthracnose symptom development in strawberry. Nevertheless, this fusA-disrupted mutant showed enhanced colonization on strawberry leaves and roots compared to the wild-type strain TP3 did. A callose deposition assay indicated that P. polymyxa TP3-directed strawberry anthracnose suppression by root-drenching required fusaricidins to enhance plant immunity. This research validates the role of fusaricidins in P. polymyxa TP3-directed induction of disease resistance and facilitates the application of P. polymyxa as a health enhancer for sustainable crop production, especially for strawberries.