Plant disease最新文献

Colletotrichum sublineola Henn. causes anthracnose disease on grain, forage, and sweet sorghum [Sorghum bicolor (L.) Moench], and on the related weed Johnsongrass [S. halepense (L.) Pers.]. Previous genetic fingerprinting studies using neutral markers indicated C. sublineola in the southeastern United States comprises two divergent populations mostly associated with the Sorghum host species. In the current study, we further characterized these populations by evaluating restriction fragment length polymorphisms (RFLPs) in fourteen putative pathogenicity-related genes (twelve small secreted-protein effector genes and two secondary metabolite-associated protein genes), and by sequencing polymorphic regions of a subset of these genes. These analyses identified three clades: one (clade A) corresponded to the previously defined population isolated mostly from S. bicolor; the other two (clades B and C) revealed further subdivision within the population recovered mostly from S. halepense. Evidence for reticulation among the gene trees suggested that the three clades correspond to genetically distinct subpopulations within C. sublineola. In greenhouse pathogenicity assays, representatives of the A clade caused disease only on S. bicolor, while clade B members caused disease only on S. halepense, and isolates belonging to clade C were pathogenic to both host species. Estimates of genetic variation indicated that the B clade was the most diverse. Members of the three subpopulations were morphologically similar but could be differentiated by single-nucleotide polymorphisms (SNPs) within a subset of the pathogenicity gene alleles, and several phylogenetic sequence markers. These SNPS could be used to identify members of the three subpopulations for future diagnostic, breeding, and research purposes.

Xanthomonas hortorum pv. carotae (Xhc) is a plant-pathogenic bacterium that causes bacterial blight of carrot. It impacts international trade due to little to no tolerance for the pathogen in carrot seed. Because the biennial crop has overlapping growing seasons and Xhc has been detected in the air in areas of carrot seed production, an improved understanding of the dispersion pathways is needed. Experiments (Airborne Xanthomonas Experiments- Madras [AXE-M]) conducted in central Oregon were designed to characterize the airborne transport and deposition of particles dispersing Xhc during harvest events. Debris samples were collected with a novel passive sampling device, the Cascade Settling Trap (CST), that sorted particles into size classes of interest as the particles were deposited out of the air column. CSTs were used during one harvest event in 2021 and three in 2022. Negative binomial regression analysis conducted on data collected in 2022 indicated that particle size and the distance from which particles were sampled can be predictive of the amount of Xhc detected. Burkard samplers were utilized in 2021 and 2022 to quantify airborne Xhc during the growing season and specific events of interest. Meteorological data, in conjunction with the use of optical particle counters, allowed for estimation of real-time airborne particle concentrations and their potential for transport. By developing a more detailed understanding of the aerobiology of Xhc, better risk assessment tools and pathogen management strategies can be employed to assess the potential for these particles to disperse Xhc across varying scales.

The Florida sugarcane industry is transitioning from manual to mechanical planting systems, which use comparatively smaller seed cane pieces (billets) as planting material. A major limitation of mechanical planting is the increased seed cane requirement due to mechanical damage and the increased vulnerability of seed cane pieces to soil-borne pathogens that cause sett rots, particularly pineapple disease caused by Thielaviopsis spp. Current sugarcane breeding programs in Florida screen for major diseases such as rusts, smut, ratoon stunting, and viruses early in the breeding process, but not for pineapple disease. This study aimed to isolate and identify Thielaviopsis spp. in the Everglades Agricultural Area (EAA), develop a single-bud inoculation protocol for greenhouse-based disease screening, and phenotype the current widely grown sugarcane varieties in Florida against Thielaviopsis spp. The pathogen was confirmed as T. ethacetica, consistent with previous reports from the EAA. A reproducible inoculation method was established and validated through symptom assessment, pathogen re-isolation, and molecular confirmation. Using this protocol, six widely grown Florida sugarcane varieties showed significantly reduced germination (by more than 50%), as well as reduced above- and below-ground morphological characteristics under infection, indicating susceptibility. Varietal differences were observed, with CP 03-1912 showing the highest mortality percentage and reduced growth under T. ethacetica infection. These findings highlight the vulnerability of current varieties to pineapple disease, especially under mechanical planting systems where smaller seed cane pieces are used. Furthermore, the developed inoculation protocol provides a scalable tool for early-stage evaluation of resistance in breeding programs, offering potential to accelerate the development of varieties better adapted to mechanical planting.

The fungal plant pathogen Ramularia crupinae is the first biological control agent approved for the management of the federally-listed noxious weed Crupina vulgaris (common crupina) in the United States. Widespread common crupina infestations threaten western U.S. rangelands and pastures by decreasing biodiversity and agricultural productivity through the displacement of native and beneficial plant species. This study reports the development of a sensitive and species-specific quantitative PCR (qPCR) diagnostic assay designed for tracking R. crupinae infections and monitoring impact following a field release. A unique group I intron located within the 18S ribosomal RNA region permitted the development of a specific and sensitive diagnostic assay capable of detecting R. crupinae in both symptomatic and asymptomatic common crupina tissue. Species-specificity was validated with no cross-reactivity against the closely related species R. acroptili and 47 common crupina fungal endophyte cultures collected from field samples prior to R. crupinae release. Serially diluted R. crupinae DNA was used to demonstrate a qPCR detection limit of 47 fg. This R. crupinae diagnostic assay is highly accurate and specific, does not require post-amplification visualization, and supports high-throughput processing of field samples, making it well suited for tracking R. crupinae establishment and spread. Monitoring R. crupinae movement is critical for studying the impact and epidemiology of this introduced biological control agent.

Sugarcane ring spot disease significantly impacts crop yield, necessitating the development of resistant cultivars. This study investigated the pathogenicity, morphology, growth characteristics, and molecular identity of the causal fungal pathogen while assessing the resistance of various sugarcane genotypes. Morphological and molecular analyses identified Curvularia guangxiensis as the primary pathogen. Pathogenicity assays demonstrated that the strain FS1 exhibited greater virulence than the strain BH1, inducing more severe leaf lesions. FS1 also displayed a higher growth rate on potato dextrose agar, triggering earlier symptom onset. A multifactorial analysis of genotype, location, and year revealed significant effects on disease incidence, with broad-sense heritability estimated at 0.7, highlighting substantial genetic and environmental contributions. Cluster analysis categorized sugarcane genotypes into five resistance groups, identifying CP81-1258 and Q202 as highly resistant, while CP88-1762, FN07-2020, and GT94-119 were highly susceptible. These findings provide critical insights for breeding resistant sugarcane cultivars and optimizing disease management strategies.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases affecting wheat production worldwide. Wheat resistant cultivars can effectively prevent and limit the occurrence and spread of the disease. The Chinese wheat landrace Laohongmai (LHM) demonstrated a high level of resistance to stripe rust at the adult plant stage. To identify and map loci associated with resistance to stripe rust in LHM, a total of 224 recombinant inbred lines (RILs) were developed by crossing LHM with Taichung 29. Maximum disease severity was assessed for the parents and RILs in the fields inoculated with currently prevalent Pst races in Langfang, Hebei, in 2023 and 2024 and in Chengdu, Sichuan, in 2024. The wheat 55K single nucleotide polymorphism array was used to genotype the RILs. A new major adult plant resistance locus, QYr.LHM-1AL, was identified and mapped to a genetic interval of 3.51 cM between the markers 45KASP1A-4 and 45SSR1A-973 on the long arm of chromosome 1AL corresponding to a 553.9-to-54.0-Mb region in the Chinese Spring reference genome. The genome region contains four genes, including TraesCS1A01G383100 encoding cysteine peptidase. The gene was found to be involved in responding to Pst invasion as confirmed by a qRT-PCR analysis. Among 50 wheat landraces tested with the three linked markers, three landraces had the LHM haplotype. The markers are useful in molecular breeding.

Cyproconazole (CPZ) was identified as a new postharvest fungicide with incomplete cross-resistance to other demethylation inhibitor fungicides registered for managing major decays of citrus. CPZ was effective on lemons, oranges, grapefruit, and mandarins, significantly reducing sour rot (Geotrichum citri-aurantii) and green mold (Penicillium digitatum). In laboratory and experimental packing line studies, CPZ was compatible with other fungicides, performed well in fruit coatings, and was effective using different application systems. CPZ at 300 to 1,250 μg/ml reduced sour rot incidence of lemons inoculated with a propiconazole (PPZ)-moderately resistant (MR) isolate of G. citri-aurantii from 87.5% in the control to between 54.6 and 13.3%, whereas. green mold caused by an imazalil (IMZ)-resistant (R) isolate of P. digitatum was reduced from 99.0% in the control to between 59.9 and 20.8%. CPZ at 1,000, 2,000, and 4,000 μg/ml in aqueous or storage coating preparations generally performed statistically similar against PPZ-sensitive (S), MR, and highly resistant (HR) isolates of G. citri-aurantii. Sour rot was reduced to zero levels with increasing concentrations for S, and MR isolates, whereas decay caused by the HR isolate was reduced from 97.1% in the control to 26.0% in storage wax treatments. For green mold and sporulation control, storage and pack coatings generally reduced the performance of CPZ, PPZ, IMZ, fludioxonil + azoxystrobin, and mixtures compared with aqueous applications. CPZ was not as effective as IMZ or fludioxonil + azoxystrobin in reducing sporulation. There was no significant difference in efficacy between heated and ambient-temperature flooder applications of CPZ or PPZ in controlling sour rot or green mold. CPZ is currently undergoing registration for postharvest use on citrus in the United States and will be an effective treatment by itself and in mixtures with other fungicides for major decays caused by S and R pathogens.

Colletotrichum species are important fungal plant pathogens associated with citrus pre- or postharvest disease globally. Seventy-three Colletotrichum isolates were collected from diseased leaves, fruits, and twigs of lime, tangerine, and pomelo in the provinces of Chiang Mai, Nakhon Pathom, and Lampang in Thailand. Colletotrichum siamense, C. gloeosporioides, C. fructicola, C. gigasporum, C. kokhaense sp. nov., C. plurivorum, and C. tropicicola were identified using morphological characters and multigene phylogenetic analysis (combinations of internal transcribed spacer, glyceraldehyde-3-phosphate dehydrogenase, Apn2-Mat1-2 intergenic spacer and partial mating type, glutamine synthetase, β-tubulin, actin, and histone depending on the species complex). C. siamense was the most prevalent species in Thailand, C. gigasporum was reported for the first time as a pathogen of citrus globally, and the new species C. kokhaense in the magnum species complex was described. Pathogenicity tests confirmed that C. siamense, C. gloeosporioides, C. gigasporum, C. kokhaense sp. nov., and C. plurivorum were pathogenic to citrus fruits, seedlings, and in planta shoots, with C. gigasporum being the most aggressive species. The non-wound inoculation technique provided good discrimination between high and low aggressive species compared with wound inoculation, where most species appeared to be very aggressive. Knowledge of Colletotrichum species causing citrus disease and their pathogenic ability will assist the development of effective disease management strategies.

The Brassicaceae invasive weed, garlic mustard (Alliaria petiolata), is a Eurasian biennial herb that has rapidly spread across North America, infesting forests and field borders and negatively impacting plant biodiversity and agroecosystem health. In 2022, a severe garlic mustard dieback event occurred in a limited section of a large, forested garlic mustard population in Maryland, U.S.A. Diseased plants were heavily defoliated, with remaining intact leaves having irregular-shaped necrotic and chlorotic lesions. Two isolates of an unknown fungal pathogen were collected, sequenced, and identified as Alternaria and confirmed to be pathogenic to garlic mustard. All inoculated garlic mustard plants rapidly developed severe symptoms within 72 h, mimicking the symptoms observed in the field. A multilocus sequence analysis identified the two strains as a distinct species that appears to be a new monotypic sister lineage to Alternaria section Sonchi and most closely related to the Japanese Apiaceae pathogen A. triangularis. This study reports the first documentation of a novel, pathogenic Alternaria species identified from the introduced range of the invasive weed garlic mustard. In addition to its potential use as a garlic mustard bioherbicide, future studies will provide critical insights in the role nonnative invasive weeds play in harboring and selecting for novel pathogenic microbes and biosecurity risks to U.S. agriculture.

Halo blight of hop, caused by Diaporthe humulicola, was first described in 2018 and is a major concern for growers in the eastern United States and Canada. This pathogen can cause quality and yield losses by desiccating hop cones, leading to shatter. However, traditional disease diagnosis is time-consuming, with morphological features taking up to 30 days to develop in culture. To address this issue, a quantitative PCR (qPCR) assay based on the translation elongation factor 1-alpha (TEF) gene was developed. We assessed capabilities and limitations of this assay for detection of D. humulicola in plant tissue and investigated aspects of the disease through (i) testing of hop rhizomes for the presence of fungal pathogens, (ii) determining the time required to detect D. humulicola in detached hop leaves, and (iii) comparing plating methods with the qPCR assay to monitor D. humulicola in a hop yard. The limit of detection for the assay was 100 fg/μl of DNA. The assay showed no cross-reactivity with other hop pathogens, endophytes, or other Diaporthe species tested. Detection of D. humulicola occurred 1 day after inoculation. The assay detected D. humulicola in both asymptomatic and symptomatic rhizome tissue, but further investigation is required to determine the cause of the observed symptoms. The assay successfully detected the pathogen in individual hop cones and inflorescences throughout the season, with higher positive identification rates than culture-based assays. This assay will provide time-limited diagnosticians with a tool for the detection of D. humulicola.