Plant disease最新文献

Rice bakanae disease (RBD), caused by Fusarium fujikuroi, threatens global rice production. While the phenylpyrrole fungicide fludioxonil shows efficacy against F. fujikuroi, resistance mechanisms remain understudied. The current study found that the fludioxonil sensitivity of 101 F. fujikuroi isolates collected in the rice fields of Xinxiang City in the Henan Province of China ranged from 0.025 to 0.759 μg/ml, with an average EC₅₀ value of 0.3441 ± 0.1961 μg/ml (standard error). Four highly fludioxonil-resistant F. fujikuroi laboratory mutants were generated by repeated exposure to fludioxonil, and they exhibited enhanced mycelial growth and sporulation but reduced spore germination, pathogenicity, and osmotic stress tolerance, alongside abnormal hyphae. Molecular analysis identified amino acid substitutions in the target protein Ffos-1, notably at residue 672 (A672P/T). These acid amino changes reduced the minimum binding energy in docking models. Ffos-1 expression was significantly (P < 0.05) upregulated in fludioxonil-resistant F. fujikuroi mutants. Meanwhile, cross-resistance analysis revealed a significant (P = 0.0064) correlation between fludioxonil and iprodione but not epoxiconazole, prothioconazole, or carbendazim. However, field monitoring is critical, as baseline shifts could compromise fludioxonil efficacy. These findings highlight Ffos-1's role in fludioxonil action and resistance, informing integrated strategies to delay resistance spread and improve RBD management.

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.

Alternaria brassicicola is the causal agent typically associated with Alternaria leaf blight and head rot (ABHR) disease in broccoli and related crops in the Eastern United States. In 2020, a new species, A. japonica, was reported as causing disease in broccoli and other vegetables in this region. We conducted a multistate pathogen survey during the growing seasons of 2022 and 2023 to assess the distribution and occurrence of A. japonica in relation to A. brassicicola in five broccoli-producing states. Our approach specifically targeted collection of broccoli leaves with lesions typical of ABHR within commercially grown fields that were managed using either organic or conventional approaches in Connecticut, Massachusetts, New York, Virginia, and Georgia. Only typical ABHR leaf lesions were selected for pathogen isolation, and subsequently, sequencing of the Alternaria major allergen a1 gene was used to identify Alternaria species. The predominant species isolated was A. brassicicola (88% in 2022 and 94% in 2023), and the second most common was A. alternata (12% in 2022 and 6% in 2023), which was obtained from fields in Connecticut and Massachusetts in 2022 and in Virginia in both years. Alternaria japonica was not found in either year. Symptoms of A. alternata were indistinguishable from A. brassicicola, as were colony morphologies. Although A. alternata is considered a generalist and of little consequence for broccoli, it is considered a pathogen of significance on multiple crops (blueberry, citrus, pistachios), but there remains scant information on the disease etiology on broccoli. Therefore, we inoculated broccoli with A. alternata in controlled conditions to shed light on possible differences in infectivity of these species on broccoli. Results of our study showed that A. alternata is pathogenic on broccoli, capable of initiating infection and causing lesions typical of ABHR. This indicates that future disease surveys of ABHR should conclusively identify the species of Alternaria that are causing disease. Additional research is needed to determine the significance of this finding in relation to yield impacts, epidemiology, fungicide resistance, and management recommendations.

Cranberries are vegetatively propagated, yet the industry lacks standardized treatments or regulations to prevent pathogen transmission through field-sourced propagative material. This study evaluated heat treatments as a potential strategy for mitigating fruit rot fungi survival. A three-part experiment was conducted. First, Colletotrichum fioriniae conidia were tested in vitro for heat tolerance, against 25, 37, 42, 44, 47, and 49°C, showing reduced survival at 44°C and complete mortality at 47°C and 49°C. Second, greenhouse trials assessed cranberry cutting survival following hot water treatments. Field-sourced cuttings of two cultivars ('Stevens' and 'Mullica Queen') were exposed to 37, 42, 44, 47, and 49°C, alongside a non-treated control (25°C). Cuttings remained viable up to 49°C, with no significant differences in survival compared to controls (P = 0.991 and P = 0.365 for 'Stevens' and 'Mullica Queen', respectively). Finally, two trials tested the efficacy of heat treatments on cuttings inoculated with C. fioriniae conidia. Treatments at 47°C and 49°C significantly improved survival for 'Stevens' (P = 0.0081 and P = 0.0045) and 'Mullica Queen' (P = 0.0427 and P = 0.00000021). These results indicate that short-duration hot water treatments can reduce survival of C. fioriniae conidia under controlled conditions while maintaining cranberry cutting viability, supporting further evaluation of heat treatment as a potential sanitation step for cranberry propagation material.

Sudden death syndrome (SDS), primarily caused by Fusarium virguliforme, threatens soybean (Glycine max) production across the United States and Ontario, Canada. SDS thrives in cool, wet soils, with post-planting rainfall exacerbating disease, making pre-planting management strategies like resistant cultivars and seed treatments crucial. This study evaluated biological and chemical seed treatments on resistant and susceptible soybean cultivars across 14 locations in 2022 and 15 locations in 2023. Data collection included final stand counts, root rot severity, foliar SDS severity index (FDX), and yield. Trials were categorized into high (FDX ≥ 10%) or low (FDX < 10%) disease severity locations based on the non-treated control (NTC). In high disease locations, cultivar and seed treatment significantly (P ≤ 0.01) influenced FDX, root rot, and yield. The base+fluopyram and base+fluopyram+natamycin treatment reduced FDX by 6.7% and increased yield by 288.5 kg/ha over the non-treated. The resistant cultivar reduced FDX by 9.7% and root rot by 2.1%, while increasing yield by 247.7 kg/ha relative to the susceptible cultivar. Under low disease pressure, cultivar selection remained significant, with resistance reducing FDX by 2.4% and root rot by 0.8%, and improving yield by 445.5 kg/ha. In contrast, the effects of seed treatment were not significant in the low disease severity environments. No seed treatments reduced FDX or root rot and only base+fluopyram and base+fluopyram+natamycin increased yield (+254 to 301 kg/ha) compared to the non-treated in the low disease severity environments. Cultivar resistance remains the most effective SDS management strategy, with seed treatments providing significant benefits under high disease pressure.

Sclerotinia sclerotiorum, the causal agent of Sclerotinia stem rot (SSR), is a fungal pathogen of soybean that can lead to yield losses of over 11 million bushels in the northern United States. While resistant cultivars can reduce SSR impacts, limited research has focused on early-maturity soybean lines adapted to the Northern Great Plains due to the lack of appropriate check lines. The primary objective was to screen early-maturity soybean lines and identify those showing consistent responses to different S. sclerotiorum isolates. In this study, we screened 193 diverse soybean lines from the United States Department of Agriculture (USDA) germplasm collection from varying maturity groups (MGs), ranging from 000 to I. Under greenhouse conditions, these lines were inoculated with a highly aggressive isolate of S. sclerotiorum, and the lesion length development was recorded at three independent time points post-inoculation. Relative Area Under Disease Progress Curve (RAUDPC) values were generated to evaluate resistance ratings. High resistance was observed in 39% of MG 000 lines, 13.8% of MG 00 lines, and 3.8% of MG 0 lines. Representative resistant, moderately resistant, and susceptible lines were subsequently evaluated against four S. sclerotiorum isolates of differing aggressiveness (WI-20, WI-43, WI-15, and WI-3). Significant line × isolate interactions were observed (P < 0.0001), but PI 194639 and PI 548649 displayed consistent resistance or susceptibility across isolates, respectively. These findings demonstrate the importance of screening with multiple S. sclerotiorum isolates and the identification of potential early-maturity soybean check lines for future SSR resistance evaluations.

Soybean cyst nematode (SCN, Heterodera glycines) is one of the most yield-limiting nematodes in soybean production. Application of synthetic nematicides is a critical component in the integrated management of SCN in China. However, resistance has developed in SCN to conventional nematicides, leading to the failure of these nematicides in some fields. It is pivotal for the soybean industry to develop new nematicides that can achieve sustainable nematode control. Seed treatment is a promising control approach. Fluopyram is widely used to control various plant-parasitic nematodes (PPNs); however, it is currently not registered as a seed treatment in China for use in controlling SCN. In this study, the efficacy of fluopyram as a seed treatment to manage SCN was evaluated through in vitro tests, greenhouse experiments, and field trials. In vitro tests showed that fluopyram caused a high mortality of H. glycines second-stage juveniles (J2s), with 50% lethal concentration (LC50) value of 0.96 mg/L that was superior to abamectin. In greenhouse experiments, compared with the untreated control, seed treatment with fluopyram at 0.15 mg active ingredient (a.i.)/seed provided significant SCN control, while maintaining excellent soybean root length and shoot fresh weight, better than the commercially available seed treatment with a 35.6% formulation of abamectin + carbendazim + thiram at 10 mL/kg seed. Moreover, in split-root experiments, fluopyram treatment at 0.15 mg a.i./seed reduced number of J2s inside the roots by 65.3% and induced resistance to SCN. Fluopyram also enhanced activities of phenylalanine ammonia-lyase (PAL) and peroxidase (POD), which was associated with the increased expressions of the defense-related genes GmNPR1-1, GmSAMT1 and GmACS9b. In two consecutive years of field trials, fluopyram seed treatment at 0.15 mg a.i./seed exhibited significant control of SCN. Compared to the control, it reduced numbers of cysts on the roots, cysts in the soil, and nematode juveniles inside the roots by 57.5%, 52.2%, 63.6% in 2023, and 63.7%, 57.2%, 67.9% in 2024, respectively. These results indicated that fluopyram not only exhibited strong nematicidal activity against H. glycines but also induced systemic resistance in soybean. In summary, fluopyram seed treatment has the potential to manage SCN in the field and warrants further studies.

Pea (Pisum sativum L.) is a cool-season annual legume crop cultivated globally. It is increasingly integrated into cereal-based rotations across Mediterranean agroecosystems, raising concerns about plant-parasitic nematodes (PPNs) that affect both legumes and subsequent crops. This study establishes the prevalence, diversity, and abundance of PPNs in a novel cropping system in southern Spain, where pea is introduced into cereal rotations. Nematode community structure in the surveyed fields is strongly influenced by intensive tillage practices and the desiccation tolerance of certain species, which facilitates their persistence through the dry summer season. The dominant PPNs affecting pea crops are Pratylenchus spp., with P. mediterraneus frequently occurring in mixed infections alongside closely related species such as P. thornei, P. neglectus, and P. crenatus. Given the absence of molecular tools specifically designed for P. mediterraneus, we developed a species-specific qPCR assay targeting P. mediterraneus and its close relative P. thornei. The newly developed qPCR assay was validated for specificity and sensitivity, and successfully applied to nematode communities extracted from pea root tissues. This molecular tool enables precise detection and quantification of P. mediterraneus and P. thornei, even in complex mixtures, offering a robust resource for nematode diagnostics and integrated management in legume-based cropping systems.