Plant disease最新文献

Potato is an important sector to the U.S. economy, and it created over $100 billion in economic activity in 2021. The U.S. exports fresh potatoes to several countries. In certain cases, fresh potato shipments from the U.S. to the international market requires the crop to be free of potato mop-top virus (PMTV). This increased the need to provide potato growers with an optional, reliable and large-scale detection method of PMTV, especially in asymptomatic tubers. We developed a duplex Immunocapture Reverse-Transcription Quantitative Polymerase Chain Reaction (IC-RT-qPCR) for the large-scale detection of PMTV in dormant tubers. The IC step eliminates the need for RNA extraction kits, making this assay appropriate for large scale tuber testing. To enhance the reliability of the current assay and reduce the chance of false negatives, a duplex format was used by deploying two primer-probe sets, including a previously reported primer-probe set targeting the RNA-CP, and a newly designed primer-probe set targeting a conserved region of RNA-TGB of PMTV genome. We also determined that peels from the stem end of the tubers were more likely to test positive for PMTV than bud end peels or lateral tuber cores. The duplex IC-RT-qPCR will provide a reliable and sensitive tool for the large-scale detection of PMTV in dormant tubers and will help safeguard potato movement in the U.S. and internationally.

The traditional understanding of begomovirus transmission exclusively through the whitefly Bemisia tabaci (Gennadius) has shifted with findings of seed transmission in some begomoviruses over the last decade. We investigated the seed transmissibility of cucurbit leaf crumple virus (CuLCrV), a bipartite begomovirus that has recently emerged as a severe constraint for yellow squash (Cucurbita pepo L.) production in the southeastern United States. We found a high concentration of CuLCrV in the male and female flower tissues of infected squash, including the pollen and ovules. The virus infiltrated the fruit tissues, including the endocarp and funiculus, which are anatomically positioned adjacent to the seeds. In seeds, CuLCrV was detected in the endosperm and embryo, where there are no vascular connections, in addition to the seed coat. The virus was detected in the radicle, plumule, cotyledonary leaves, and true leaves of seedlings grown from seeds collected from infected fruits. In the grow-out test conducted, CuLCrV infections ranged from 17 to 56% of the progeny plants. To ensure that partial viral genome fragments were not being mistaken for replicative forms of the virus, we performed rolling circle amplification PCR and amplified complete DNA-A and DNA-B of CuLCrV from seed tissues, seedlings, and progeny plants of CuLCrV-infected squash. Near-complete DNA-A and DNA-B sequences of CuLCrV were recovered from a progeny plant, further validating our findings. Our results demonstrate that CuLCrV can translocate from vegetative to reproductive tissues of yellow squash, persist within the seeds, and subsequently induce infection in progeny plants, confirming its capacity for seed transmission.

Codiaeum variegatum is a valuable ornamental plant with distinct bright yellowing and golden spots on dark green leaves, which resemble virus symptoms. To investigate the factors, especially viral agents, associated with the variegated leaf color of C. variegatum, we performed virome profiling of a single C. variegatum 'Gold Dust' leaf sample collected from Hainan, China, using ribosomal RNA-depleted total RNA sequencing on an Illumina NovaSeq 6000 platform. Two novel viruses, with two variants each, belonging to the family Closteroviridae, were detected and characterized: Croton golden spot-associated virus C variants 1 and 2 (CGSaVC-v1 and CGSaVC-v2) of the genus Crinivirus and Croton golden spot-associated virus A variants 1 and 2 (CGSaVA-v1 and CGSaVA-v2) of the genus Ampelovirus. Transmission electron microscopy showed long, flexuous, filamentous virus particles approximately 15 nm in diameter and 760 to 770 nm in length. Molecular screening of 97 variegated individual plant leaves showed a high prevalence of CGSaVA-v2 (90.7%), CGSaVA-v1 (75.3%), CGSaVC-v1 (70.1%), and CGSaVC-v2 (47.4%), while asymptomatic leaves near the meristem tip were mostly free of the target viruses. To our knowledge, this is the first study to demonstrate the significant association between closterovirids and the golden spots. The findings provide novel insights into the genetic diversity of the family Closteroviridae and inform future germplasm conservation and new cultivar development of C. variegatum.

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a continuous threat to global wheat production. In 2021, the epidemic of wheat stripe rust in China affected approximately 4.5 million hectares, resulting in severe yield losses. When confronted with the epidemic, tracing the sources of the pathogen can offer valuable insights for disease prevention and control. This study was conducted to analyze the genetic structure, aerodynamics, geographical features, and cultivation practices of the pathogen population in various wheat-producing regions and to further reveal the spread patterns of the stripe rust pathogens in China. The findings indicated an overall trend of the pathogen dissemination from the west to the east. The pathogen was primarily spread from the northwestern region to the Huang-Huai-Hai region through the Guanzhong Plain and the NanXiang Plain. Meanwhile, the pathogen also spread eastward from the southwestern region to the lower reaches of the Yangtze River, using the Jianghan Plain as a bridge and the Yangtze River Valley in southwestern Anhui as the main pathway. Furthermore, the pathogen spread northward into Shandong under the driving force of the southeast winds. The findings of this study may provide valuable insights for the integrated management of wheat stripe rust in China.

Gummy stem blight (GSB), caused primarily by the fungus Stagonosporopsis citrulli in the Southeastern United States, affects cucurbits and is particularly destructive on watermelon. Previous epidemiological models of GSB constructed for greenhouse cucumber showed leaf wetness and temperature were the primary and secondary environmental factors, respectively, that explained epidemic progress. The objective of this study was to construct a model that predicted GSB severity on field-grown watermelon based on environmental factors. Disease and weather data from six fungicide experiments in Charleston, South Carolina, in the spring and fall of 1997 and the fall seasons of 2017, 2018, 2019, and 2022 were used as inputs. Fungicide treatments were grouped into nonsprayed, protectant (chlorothalonil and mancozeb), and GSB-specific (cyprodinil, difenoconazole, and fludioxonil) applications. Cumulative hours of leaf wetness were the primary explanatory variable that modeled the increase in proportion GSB severity ≥2% across all epidemics. Incorporation of temperature or other environmental variables did not improve the model. Fit of the overall model was evaluated with k-fold cross-validation, where individual experiments were each excluded from the model-fitting process. Slopes of predicted disease progress curves were lowered significantly compared with the nonsprayed treatments by applications of protectant fungicides. Applying GSB-specific fungicides alternated with chlorothalonil further reduced slope values. The model successfully predicted progress of GSB epidemics under different weather patterns and fungicide applications.

Verticillium wilt (VW), caused by the soilborne plant pathogenic fungus Verticillium dahliae, is a major disease affecting olive crops globally. In view of the lack of effective postinfection treatments, exclusion and avoidance strategies are essential in disease management. Assessing the risks posed by this pathogen is essential to prevent the spread and to ensure selection of suitable sites for new plantations. This study aimed to elucidate the environmental factors driving V. dahliae establishment in the Andalusia region in southern Spain, an emblematic Mediterranean landscape for olive cultivation. To this end, we explored ecological niche signals for this fungal pathogen by analyzing 62 environmental variables across 1.6 million ha dedicated to olive and cotton cultivation by using data from a 15-year survey on the presence or absence of VW incidence from both olive and cotton fields. To ensure robust identification of ecological niche signals, we employed randomization-based, nonparametric univariate tests to compare presence records with the broader sampling universe (including absence records). Our findings identified key environmental variables that are associated significantly with V. dahliae presence, including temperature range seasonality (including mean diurnal and annual ranges), summer temperature (maximum of the warmest month, mean of the warmest quarter), and moisture and water availability (near-surface humidity, potential evapotranspiration, vapor pressure) as core niche variables for V. dahliae. Our results replicated the pathogen's known distribution, identifying the Guadalquivir Valley as a particularly high-risk area in view of its mild winters and distinct rainy seasons, providing new insights into the specific environmental conditions that facilitate the pathogen's survival and spread. Furthermore, this study introduces a novel approach to niche modeling that prioritizes variables with consistent effects and significant impact on the presence and distribution of V. dahliae and identifies potential data artifacts. This approach enhances our understanding of ecological requirements in V. dahliae and informs targeted management strategies.

Fusarium solani species complex (FSSC) is a causal agent of collar rot and fruit rot in passion fruit worldwide. This study investigated the diversity and characteristics of FSSC isolates causing collar rot and fruit rot in Taiwanese passion fruit. Thirty-five FSSC isolates were harvested from collar rot and fruit rot samples of passion fruit from various cultivars and different geographical locations in Taiwan. The majority of these FSSC isolates caused collar rot and fruit rot disease of varying virulence in the stems and fruits of the purple and yellow cultivars of passion fruit. FSSC isolates were categorized into four groups: F. solani-melongenae (FSSC 21; n = 29), F. solani (FSSC 5; n = 1), F. liriodendri (FSSC 24; n = 1), and an unknown group (n = 4) based on the phylogenetic analysis of internal transcribed sequence (ITS), translation elongation factor 1 alpha (TEF-1α), and RNA polymerase II subunit 2 (RPB2) sequences. In Taiwan, F. solani-melongenae was the dominant species causing collar rot and fruit rot in passion fruit. F. solani-melongenae was a homothallic fungus that produced perithecia in diseased tissues. However, F. solani and F. liriodendri did not produce perithecia. The unknown FSSC group showed morphological characteristics similar to F. solani-melongenae and produced perithecia. Phylogenetic analysis based on the ITS and TEF-1α sequences demonstrated that the Taiwanese FSSC isolates were distinct from the Brazilian and Chinese FSSC isolates. In summary, FSSC isolates causing collar rot and fruit rot of Taiwanese passion fruit showed high diversity, potentially associated with the geographical locations.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is the most destructive fungal disease affecting wheat in China, especially in Shaanxi Province, an important epidemiological region connecting the western Pst oversummer regions and the central and eastern spring epidemic regions in the country. In the present study, 291 Pst isolates from Shaanxi Province were studied for their virulence using two sets of wheat differentials, population structure using single-nucleotide polymorphism (SNP) markers, and sensitivity to triadimefon. When the isolates were tested on the Chinese differentials of 19 wheat cultivars, 72 races were identified, which belonged to three groups, including the Guinong 22 group (48.45%), Hybrid 46 group (31.62%), and Suwon 11 group (19.93%). The three most predominant races were CYR34 (15.46%), G22-14 (11.68%), and CYR32 (10.65%). When the isolates were tested on the 18 Yr single-gene differentials, 95 races were identified, but none of the isolates were virulent to either Yr5 or Yr15. Cluster analyses of the virulence data based on the two sets of differentials and the SNP marker data consistently separated the Shaanxi Pst population into two clusters in the central part and southern part of the province. Triadimefon sensitivity testing across different concentrations showed a broad range of half-maximal effective concentration (EC₅₀) values, from 0.03 to 5.99 μg ml^-1, with a mean EC₅₀ value of 0.46 μg ml^-1. The majority of isolates (90.72%) were sensitive to the fungicide. The correlation analyses of the virulence, SNP marker, and the triadimefon sensitivity data showed no significant correlations, except a logarithmic relationship between the EC₅₀ value and the number of avirulence factors. This study is the first to determine the relationship of virulence and SNP markers with triadimefon sensitivity in a regional Pst population. The findings provide valuable insights for breeding resistant wheat cultivars and integrated management of stripe rust.