Plant disease最新文献

Seed rot and damping-off of alfalfa (Medicago sativa L.) is caused by a soilborne disease complex resulting in thin initial stands of plants with continuing damage during wet soil conditions decreasing forage yields and winter survival. Apron (metalaxyl) and Apron XL (mefenoxam) have been used on alfalfa seeds for decades to reduce damping-off and early season root rot. Although several other anti-oomycetes (oomicides) and fungicides are labeled for use on alfalfa seeds, there is little information on their efficacy against specific pathogens or the disease complex. Our objective was to test chemical seed treatments to identify those with broad antimicrobial activity to aid in establishing alfalfa stands where pathogen complexes are present. First, 10 products were tested for mycelial growth inhibition of nine alfalfa pathogens. The two most promising, EverGol Energy and Intego Solo, were active against Globisporangium ultimum, Pythium irregulare, P. sylvaticum, P. paroecandrum, Aphanomyces euteiches, and Phytophthora medicaginis. Protection of seedlings in agar plate bioassays and infested soil assays against G. ultimum and Pythium species by EverGol Energy was like that of Apron XL, whereas Intego Solo was not effective. The EverGol Energy seed treatment provided modest protection in bioassays with A. euteiches and P. medicaginis for susceptible cultivars, although it did not improve protection for resistant cultivars. Combined seed treatments did not improve seedling health in single pathogen bioassays or experiments with naturally infested field soil with multiple pathogens. Seed treatments with Apron and Apron XL were the most effective in providing partial protection against the disease complex in field soil. These results suggest that greater resistance is needed for managing the disease complex.

Xylella fastidiosa (Xf) is a quarantine plant pathogen in the European Union, recognized as a high-priority pest due to its devastating cultural and economic impact on crops, ornamental plants, and landscape vegetation. The development and implementation of reliable, sensitive, and specific diagnostic methods for Xf detection are critical to ensure the production and trade of healthy plant material and to facilitate effective control measures, primarily aimed at eradication. Despite the availability of numerous detection protocols, their diagnostic parameters remain not precisely defined, and no universally accepted gold standard protocol exists. This study compared the global accuracy and performance of six molecular assays using almond samples collected from naturally infected almond trees in the Alicante Demarcated Area, Spain. Additionally, the study evaluated the influence of plant sample type (leaf petioles versus woody chips) on diagnostic accuracy. Harper-qPCR and Li-qPCR assays demonstrated the highest sensitivity, with detection limits as low as 2.8 to 3 fg of Xf DNA. Droplet digital PCR (ddPCR) exhibited excellent sensitivity for woody chip samples, while Li-qPCR showed superior specificity across both tissue types. In contrast, recombinase polymerase amplification displayed lower detection limits and reproducibility compared with qPCR-based methods. Bayesian latent class models indicated that combining Harper-qPCR and Li-qPCR for petioles, or Harper-qPCR and ddPCR for wood samples, optimized diagnostic reliability by reducing false negatives, which is critical in buffer zones under eradication while maintaining high specificity. These findings emphasize the need for tailoring diagnostic protocols to the epidemiological context, balancing sensitivity and specificity to optimize surveillance schemes for Xf and to support effective phytosanitary management strategies.[Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Cercospora leaf blight (CLB) of soybean is caused by multiple Cercospora species globally, presenting significant challenges to disease management. The lack of standardized methods for inoculating and inducing CLB symptoms in controlled environments inhibits experiments on pathogen biology and host resistance. Consequently, limited understanding of the biology and epidemiology of these pathogens prohibits the development of tailored management strategies. Inducing sporulation of Cercospora species associated with CLB on amended media has been challenging, and the recommendations in the literature are inconsistent. To address these issues, standardized protocols were developed for inducing sporulation and reproducing CLB symptoms in controlled environments. Eleven culture media were tested for Cercospora cf. flagellaris conidial production, with V8 agar (V8A) being the most effective. Five V8A concentrations were tested, and the conidia were harvested between 3 and 7 days with the highest conidial production (4.3 × 10⁵ per ml) occurring on day 4 with 30% V8A. Peak sporulation varied, with C. cf. flagellaris peaking on day 4 and Cercospora cf. sigesbeckiae, Cercospora kikuchii, and Cercospora iranica peaking on day 3. Pathogenicity tests under controlled conditions fulfilled Koch's postulates by reproducing symptoms for all species tested, confirming their role in CLB development. These protocols provide the first standardized, efficient, and reproducible methods for Cercospora sporulation and inoculation. These methods offer insights for fundamental research into Cercospora biology and their interactions with soybeans, ultimately improving CLB management.

Passion fruit and its seedlings hold significant economic value for both domestic and export markets in Taiwan. Among the diseases affecting passion fruit, Phytophthora blight, caused by Phytophthora nicotianae, severely impacts seedling survival and fruit production. This study aimed to develop a microbial agent to control Phytophthora blight by evaluating the potential of Streptomyces cavourensis strain PES4, isolated from rhizosphere soils in Taiwan. Additionally, the impact of strain PES4 application on microbial communities in the field was investigated. Our results demonstrated that S. cavourensis PES4 exhibited strong antagonistic activity against several bacterial, fungal, and oomycete pathogens, including P. nicotianae. Applying a 100-fold diluted culture broth of strain PES4 significantly reduced the severity of Phytophthora blight on passion fruit leaves and fruits. Weekly applications of strain PES4 throughout the growing season enhanced plant growth, yield, and fruit quality compared with the water control. Next-generation sequencing was used to analyze the influence of strain PES4 application on the rhizosphere microbiome. The application of strain PES4 did not affect microbial richness or diversity but did alter the composition of bacterial and fungal communities. Specifically, strain PES4 application reduced the relative abundances of Proteobacteria and Actinobacteria while increasing Acidobacteria, Verrucomicrobia, and Gemmatimonadetes at the phylum level. At the genus level, Rhodanobacter and Streptomyces populations increased. Regarding fungal communities, strain PES4 application promoted the populations of Trichoderma and Mortierella, while Penicillium and Colletotrichum populations declined. In conclusion, S. cavourensis PES4 is a promising plant probiotic with both growth-promoting and biocontrol activities against Phytophthora blight in passion fruit. Its application can modulate the rhizosphere microbiome by enhancing beneficial bacterial and fungal populations and suppressing plant pathogenic ones, suggesting its potential as a sustainable biocontrol agent.[Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Cranberry false blossom disease (CFBD) has posed significant threats to cranberry (Vaccinium macrocarpon Ait.) cultivation since its emergence in the late 19th century. This study reviews the epidemiology, historical management strategies, and recent resurgence of CFBD, with a focus on its causal phytoplasma pathogen and insect vector, the blunt-nosed leafhopper (BNLH), and the implications for disease control. Initial outbreaks in Wisconsin were characterized by floral phyllody and abnormal shoot development, and early misattribution of the disease to abiotic factors delayed effective interventions. The identification of BNLH as the primary vector catalyzed the development of integrated management strategies, including vector control through insecticides, flooding, and sanding, as well as the establishment of certification programs to restrict the spread of infected propagation material. Early cranberry breeding programs identified landraces with lower CFBD field incidence, and which were non-preferred for feeding by BNLH, leading to the first generation of improved cranberry cultivars. Despite successful suppression post-1950, CFBD has re-emerged since 2010, correlating with shifts in integrated pest management practices and the adoption of high-yielding cranberry cultivars lacking resistance screening. The resurgence underscores the need for renewed focus on vector monitoring, the development of resistant cultivars, and an understanding of phytoplasma-vector-host interactions. Contemporary management requires interdisciplinary collaboration, incorporating advances in molecular diagnostics, eco-epidemiological modeling, and breeding programs prioritizing CFBD resistance. The historical insights into CFBD control, combined with modern scientific approaches, provide a framework for mitigating current and future outbreaks, ensuring the sustainable production of cranberries in North America and beyond.

Reynoutria japonica (Polygonaceae) is widely considered one of the most persistent and problematic non-native invasive weeds introduced to North America. Conventional methods to manage infestations are labor-intensive and often require annual monitoring and re-treatment. Biological control agents (BCAs) present an alternative management strategy. Currently, few organisms are effective for managing Re. japonica, presenting a need to discover additional candidate BCAs. Recently, leaf spots were observed on Re. japonica in two locations in the eastern United States, and the causal agent was investigated as a potential BCA. In this study, fungi isolated from symptomatic Re. japonica were identified as belonging to a previously undescribed species of Didymella based on DNA sequence homology, phylogenetic analysis, and morphological characteristics. The host range of related Didymella spp. includes other polygonaceous plants, notably cultivated Rheum rhabarbarum. Therefore, the pathogenicity of isolates representing this new fungal species was tested on seedlings of Re. japonica and Rh. rhabarbarum 'Victoria'. The novel species was capable of infecting both Re. japonica and Rh. rhabarbarum under artificial conditions. An isolate of D. rhei (Ellis & Everh.) Qian Chen & L. Cai, a close relative and known pathogen of Rh. rhabarbarum, was included in pathogenicity tests but failed to cause disease on Re. japonica. The pathogen from Re. japonica was described as D. polygonacearum sp. nov. This study suggests D. polygonacaeum is a poor candidate for biological control use and that Re. japonica may harbor crop pathogenic microbes.

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.