Plant disease最新文献

Acidovorax citrulli infects seedlings, adult plants, and fruits, causing bacterial fruit blotch (BFB) in watermelon. Host resistance would provide an effective and economical management option for BFB, but there are currently no resistant watermelon cultivars. Several resistant accessions were previously identified in the U.S. Department of Agriculture's (USDA) Citrullus amarus collection. Identifying the genetic basis of this resistance would allow the development of BFB-resistant cultivars through introgression from this crop wild relative. Genome-wide association studies (GWAS) are an excellent tool for dissecting the genetic architecture of a trait. The USDA's Citrullus amarus collection (N = 127 accessions) was genotyped with whole genome resequencing, resulting in 2,126,759 single nucleotide polymorphism (SNP) markers, then phenotyped for BFB resistance and used for GWAS of seedling resistance to A. citrulli. Four models were used for GWAS in R with the GAPIT package. Mixed linear model and multilocus mixed linear model analysis did not identify any significant marker associations. Fixed and random circulating probability unification identified three quantitative trait nucleotides (QTN) on chromosomes 2, 4, and 8. Bayesian-information and linkage-disequilibrium iteratively nested keyway identified only one significant QTN on chromosome 8. The three significant QTNs explained 65.1% of the phenotypic variance using a linear regression model. Putative candidate genes within the linkage disequilibrium blocks of significant SNPs code proteins relevant to biotic resistance, such as Patellin-6, macrophage migration inhibitory factor homolog, prenylated Rab acceptor 1 family protein and trichome birefringence-like family proteins. The predictive ability of six genomic prediction models for A. citrulli seedling resistance ranged from 0.45 to 0.75. Along with identifying genomic regions associated with BFB seedling resistance, this study observed moderate to high predictive abilities across genomic prediction models.

Fusarium root rot on ginseng is an important root disease that seriously affects ginseng (Panax ginseng) yield and quality. However, the species categories and distribution of Fusarium causing ginseng root rot in China have not been systematically examined. A total of 571 pure Fusarium isolates were obtained from 2018 to 2019 from 14 ginseng-producing regions in Jilin, Liaoning, and Heilongjiang provinces, China. Based on multilocus sequence analysis of ITS-tef1-rpb2 and morphological characteristics, the 571 Fusarium isolates were identified as F. oxysporum (accounting for 47.46% of the total isolates), F. solani (35.38%), F. equiseti (5.78%), F. proliferatum (2.80%), F. cerealis (1.75%), F. semitectum (1.75%), F. acuminatum (1.75%), F. redolens (1.58%), F. verticillioides (1.05%), and F. graminearum (0.70%). Among them, F. oxysporum and F. solani were the dominant species, and F. graminearum and F. verticillioides were first recorded on ginseng in China. The fungicides captan and hymexazol were tested in vitro for their inhibitory activities against 10 Fusarium species. All Fusarium species displayed enhanced sensitivity to captan compared with hymexazol. The protective effects of captan against ginseng root rot caused by F. oxysporum ranged from 94.07 to 97.78% at concentrations of 200, 400, and 600 μg·ml^-1; however, its curative effects were much lower, ranging from 29.63 to 35.56%. In comparison, hymexazol exhibited protective effects of only 24.00 to 52.00% and curative effects of 16.00 to 45.33% at concentrations of 600 to 1,000 μg·ml^-1. In addition, microconidia were highly sensitive to both fungicides, compared with mycelia and macroconidia.

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.

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.

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.

Allo-inoculum has an important role in fungal disease epidemiology. Understanding the factors that impact the long-distance dispersal of a pathogen is crucial to improve its management. In this study, we studied Pseudocercospora fijiensis allo-inoculum dynamics in Martinique over a period of 18 months. We used trap plants to measure (10 times) the spore abundance across six locations. Lesion densities observed on trap plants were used as a proxy of the allo-inoculum resulting from long-dispersal ascospores. We analyzed how the lesion densities of P. fijiensis measured with trap plants were statistically correlated with (i) weather factors and (ii) the stage of evolution of disease (SED) measured in closest banana plots. The SED measured in neighboring plots did not significantly influence the lesion densities observed on the trap plants. For each variable, we determined the period of time prior to the trap plant exposure that exhibited the strongest correlation with the lesion densities measured on these plants. Rainfall was the variable with the most influence and positively correlated with lesion densities when measured 7 to 4 days before trap plant exposure. Inversely, there was a negative correlation with UV radiation measured 2 to 1 days prior to trap plant exposure. This information complements the knowledge on the biology of the fungus and holds potential for enhancing disease management, especially the importance of rainfall for the allo-inoculum dynamics. These results also showed that if commercial farms have good management of black leaf streak disease, it does not contribute to long-distance contamination.

Olive leaf spot, also called peacock eye disease, is caused by the hemibiotrophic plant pathogen Venturia oleaginea. Disease symptoms develop on the upper side of leaves; infected leaves eventually abscise; and in severe epidemics, the trees are completely defoliated. Despite the vast knowledge gained about the pathogen and the disease since it was first described in 1845, observations made in recent years in commercial olive groves in Israel remain unexplained. The long-term objective of this study was to establish guidelines for disease management strategies in commercial olive groves in Israel. To achieve this, we first needed to comprehend the development and progression of the disease in the region. We determined that in each growing season, infections could occur in both autumn and spring. Furthermore, there were two episodes of disease development: the first between the end of autumn and the beginning of winter, and the second between the spring and early summer. The data were used to propose a model for peacock eye development that implies that V. oleaginea maintains monocyclic and polyetic characteristics in the Mediterranean climatic conditions prevailing in Israel: the disease is monocyclic because it completes only one disease cycle within a certain growing season; it is polyetic because infections occurring in one growing season remain asymptomatic until the succeeding season.

Powdery mildew, caused by Podosphaera xanthii, poses a significant threat to watermelon (Citrullus lanatus) cultivation. Development of resistant cultivars is one of the best strategies to manage powdery mildew. To elucidate the genetic basis of resistance, bulked segregant analysis (BSA) was conducted on an F₂ population derived from a cross between resistant (USVL608-PMR) and susceptible (USVL677-PMS) genotypes. A 570-kb region on chromosome 2 was identified using QTLseq, containing 99 single-nucleotide polymorphisms (SNP) and eight putative genes. A tightly linked kompetitive allele specific PCR (KASP) marker was developed and validated across three F₂ populations (USVL608-PMR × USVL677-PMS, USVL608-PMR × 'Sugar Baby,' USVL608-PMR × 'Dixie Lee'), showing a 3:1 segregation ratio and very strong linkage to resistance. Marker-disease resistance linkage was further validated in the F₃ generation of all three populations. RNAseq analysis revealed the upregulation of lipoxygenase (LOX), jasmonic acid (JA), and reactive oxygen species (ROS) pathways after inoculation, suggesting their role in powdery mildew resistance in watermelon. The development of tightly linked KASP markers in three different backgrounds for powdery mildew resistance and a molecular understanding of disease resistance will be useful for breeding and selecting new disease-resistant watermelon cultivars.

We recently provided new insights into the etiology of Venturia oleaginea, the causal agent of peacock eye disease in olive. We identified two distinct periods of infection events during each growing season: the first in autumn and the second in the spring. In addition, we reported the occurrence of two episodes of disease development: the first at the end of autumn/beginning of winter and the second in the spring and early summer. The main goal of the current study was to experimentally examine the practical implementation of these new insights. Four experiments were performed in the 2021/2022 and 2022/2023 seasons in commercial groves under natural epidemics. The results demonstrated that application of one or two sprays before or after the first major rain event in the season (the presumed time of infections that generate the second disease episode) significantly reduces disease development. The level of disease suppression achieved by these sprays was not inferior to the level of disease control achieved by nine consecutive sprays in a season. The effect of the application in one season on peacock eye development in the following season was evaluated in the same groves, and it was found that if the disease is not controlled during two consecutive seasons, its severity increases markedly in the succeeding season. However, if the disease is properly managed in the first season, its severity in the succeeding season may be minute or even nonexistent.

Bacterial gall caused by Pseudomonas amygdali pv. loropetali (PAL) is a prevalent problem on Loropetalum chinense shrubs in commercial plant nurseries. A method was developed to reliably detect PAL on the surface of loropetalum twigs. A whole-genome analysis resulted in the identification of a locus encoding an AraC regulator that is specific to PAL. A pair of primers and a TaqMan probe were designed based on a 71-base-pair sequence in this locus. Positive results of PCR amplification were obtained with genomic DNA samples from all PAL strains but not from those of other Pseudomonas species, Agrobacterium tumefaciens, or Burkholderia contaminans. Melting curve analysis demonstrated that all PAL PCR products shared the same melting temperature of 79°C. TaqMan-based quantitative PCR (qPCR) analysis of the serially diluted genomic DNA from PAL strain AAC exhibited a strong linear response for regressed cycle threshold and logarithm copy values (adjusted R² = 0.9944) with a high amplification efficiency (E = 1.96), whereas the linear response (adjusted R² = 0.8885) for PAL genomic DNA extracted from serially diluted bacterial cell suspension had a reduction in detection sensitivity. The limits of detection and quantification of PAL from the spiked plant twigs (diameter × length = ∼0.45 × 2.45 cm) were 873 and 14,724 cells, respectively, using a modified Promega Wizard extraction protocol. These limits of the qPCR method, although restrictive, still allow a practical detection of PAL strains associated with plant tissue that can be used in epidemiological studies to develop disease management options.