Phytopathology最新文献

In this study, in planta assays were conducted to assess the effects of fungicide spray tactics, such as the reduction of the labeled fungicide dose and mixture with a multisite fungicide, on fungicide resistance selection and disease control using Vitis vinifera 'Cabernet Sauvignon' grown in a greenhouse for 2 years. The entire clusters were inoculated with Botrytis cinerea isolates at varying frequencies of fenhexamid resistance, followed by fungicide sprays and disease and fenhexamid resistance investigations at critical phenological stages. Our findings indicate that the lower dose of the at-risk fungicide, fenhexamid, effectively managed fenhexamid resistance and disease as well as the higher, labeled dose. In addition, a mixture with the multisite fungicide captan generally resulted a net-positive effect on both resistance management and disease control.

The commercialized genetically modified (GM) papaya cultivars have protected papaya from the devastating disease caused by papaya ringspot virus (PRSV). However, papaya leaf distortion mosaic virus (PLDMV), which causes similar infection symptoms but is serologically distinct from PRSV, was found as a competitive threat to the papaya industry. Our study surveyed the occurrence of PRSV and PLDMV as well as the transgenic markers of the 35S promoter from cauliflower mosaic virus (CaMV 35S) and the neomycin phosphotransferase II (NPT II) gene in feral papaya plants, which were found frequently growing outside of cultivated papaya fields on Hainan Island. In total, 123 feral papayas, comprising 62 (50.4%) GM plants and 61 (49.6%) non-GM ones, were sampled. Among them, 23 (18.7%) were positive for PRSV, 49 (39.8%) were positive for PLDMV, including 5 plants co-infected by PRSV and PLDMV, and 56 (45.5%) plants were free of either virus. In traditional papaya growing regions, we detected fewer PRSV-infected plants (2 in 33, 6%) than in other regions (21 in 90, 23%). But overall, whether transgenic or not made no significance in PRSV incidence (P=0.230), with 9 PRSV-infected plants among 62 GM papayas and 14 among 61 non-GM papayas. Phylogenetic and genetic differentiation analysis showed a clear correlation between PRSV and PLDMV populations and their geographical origins. Negative selection was estimated for the selected gene regions of both viruses. Notably, PLDMV has deviated from neutral evolution and experienced population expansion, exhibiting increased genetic diversity and is becoming the predominant threat to papaya in Hainan.

Grapevine downy mildew (GDM), caused by the oomycete Plasmopara viticola, can cause 100% yield loss and vine death under conducive conditions. High resolution multispectral satellite platforms offer the opportunity to track rapidly spreading diseases like GDM over large, heterogeneous fields. Here, we investigate the capacity of PlanetScope (3 m) and SkySat (50 cm) imagery for season-long GDM detection and surveillance. A team of trained scouts rated GDM severity and incidence at a research vineyard in Geneva, NY, USA from June to August of 2020, 2021, and 2022. Satellite imagery acquired within 72 hours of scouting was processed to extract single-band reflectance and vegetation indices (VIs). Random forest models trained on spectral bands and VIs from both image datasets could classify areas of high and low GDM incidence and severity with maximum accuracies of 0.85 (SkySat) and 0.92 (PlanetScope). However, we did not observe significant differences between VIs of high and low damage classes until late July-early August. We identified cloud cover, image co-registration, and low spectral resolution as key challenges to operationalizing satellite-based GDM surveillance. This work establishes the capacity of spaceborne multispectral sensors to detect late-stage GDM and outlines steps towards incorporating satellite remote sensing in grapevine disease surveillance systems.

Rice production worldwide is threatened by the disease Bacterial Panicle Blight (BPB) caused by Burkholderia glumae. Despite the threat, resources to control this disease such as completely resistant cultivars or effective chemical methods are still lacking. However, the need to control this disease has paved the way to explore biologically based approaches harnessing the antimicrobial activities of environmental bacteria. Previously, the bacterium Pseudomonas protegens PBL3 was identified as a potential biological control agent against B. glumae due to its antimicrobial activity against B. glumae. Such antimicrobial activity in vitro and in planta was associated with the P. protegens PBL3 bacteria-free secreted fraction (secretome), although the specific molecules responsible for this activity have remained elusive. In this work, we advance the characterization of the P. protegens PBL3 secretome, by evaluating the antimicrobial activity in vitro of selected secondary metabolites predicted by the P. protegens PBL3 genomic sequence against B. glumae. In addition, using Reversed Phase Liquid Chromatography Tandem Mass Spectrometry (RPLC-MS/MS), of the P. protegens PBL3 secretome, enabled us to successfully detect and quantify Pyoluteorin, 2,4-diacetylphloroglucinol (2,4-DAPG) and Pyochelin. Among those, Pyoluteorin and 2,4-DAPG reduced the growth of B. glumae in vitro along with reducing the symptoms of BPB and bacterial growth in planta, suggesting that these compounds could be effective as biopesticides to mitigate BPB.

Austropuccinia psidii is the causal pathogen of myrtle rust disease of Myrtaceae. To gain understanding of the initial infection process, gene expression in germinating A. psidii urediniospores and in Leptospermum scoparium-inoculated leaves were investigated via analyses of RNA sequencing samples taken 24 and 48 h postinoculation (hpi). Principal component analyses of transformed transcript count data revealed differential gene expression between the uninoculated L. scoparium control plants that correlated with the three plant leaf resistance phenotypes (immunity, hypersensitive response, and susceptibility). Gene expression in the immune resistant plants did not significantly change in response to fungal inoculation, whereas susceptible plants showed differential expression of genes in response to fungal challenge. A putative disease resistance gene, jg24539.t1, was identified in the L. scoparium hypersensitive response phenotype family. Expression of this gene may be associated with the phenotype and could be important for further understanding the plant hypersensitive response to A. psidii challenge. Differential expression of pathogen genes was found between samples taken 24 and 48 hpi, but there were no significant differences in pathogen gene expression that were associated with the three different plant leaf resistance phenotypes. There was a significant decrease in the abundance of fungal transcripts encoding three putative effectors and a putative carbohydrate-active enzyme between 24 and 48 hpi, suggesting that the encoded proteins are important during the initial phase of infection. These transcripts, or their translated proteins, may be potential targets to impede the early phases of fungal infection by this wide-host-range obligate biotrophic basidiomycete.

Valsa pyri, the causal agent of pear canker disease, typically induces cankers on the bark of infected trees and even leads to tree mortality. Secondary metabolites produced by pathogenic fungi play a crucial role in the pathogenic process. In this study, secondary metabolic regulator VpLaeA was identified in V. pyri. VpLaeA was found to strongly affect the pathogenicity, fruiting body formation, and toxicity of secondary metabolites of V. pyri. Additionally, VpLaeA was found to be required for the response of V. pyri to some abiotic stresses. Transcriptome data analysis revealed that many of differentially expressed genes were involved in the secondary metabolite biosynthesis. Among them, about one third of secondary metabolite biosynthesis core genes were regulated by VpLaeA at different periods. Seven differentially expressed secondary metabolite biosynthesis core genes (VpPKS9, VpPKS10, VpPKS33, VpNRPS6, VpNRPS7, VpNRPS16, and VpNRPS17) were selected for knockout. Two modular polyketide synthase genes (VpPKS10 and VpPKS33) that were closely related to the virulence of V. pyri from the above seven genes were identified. Notably, VpPKS10 and VpPKS33 also affected the production of fruiting body of V. pyri but did not participate in the resistance of V. pyri to abiotic stresses. Overall, this study demonstrates the multifaceted biological functions of VpLaeA in V. pyri and identifies two toxicity-associated polyketide synthase genes in Valsa species fungi for the first time.

Net blotch disease caused by Drechslera teres is a major fungal disease that affects barley (Hordeum vulgare) plants and can result in significant crop losses. In this study, we developed a deep learning model to quantify net blotch disease symptoms on different days postinfection on seedling leaves using Cascade R-CNN (region-based convolutional neural network) and U-Net (a convolutional neural network) architectures. We used a dataset of barley leaf images with annotations of net blotch disease to train and evaluate the model. The model achieved an accuracy of 95% for Cascade R-CNN in net blotch disease detection and a Jaccard index score of 0.99, indicating high accuracy in disease quantification and location. The combination of Cascade R-CNN and U-Net architectures improved the detection of small and irregularly shaped lesions in the images at 4 days postinfection, leading to better disease quantification. To validate the model developed, we compared the results obtained by automated measurement with a classical method (necrosis diameter measurement) and a pathogen detection by real-time PCR. The proposed deep learning model could be used in automated systems for disease quantification and to screen the efficacy of potential biocontrol agents to protect against disease.

'Candidatus Liberibacter asiaticus', the putative causal agent of citrus greening disease, is transmitted by the Asian citrus psyllid, Diaphorina citri, in a propagative, circulative, and persistent manner. Unfortunately, 'Ca. L. asiaticus' is not yet available in pure culture to carry out Koch's postulates and to confirm its etiology. When a pure culture is available, an assay to test its infectivity in both the insect vector and the plant host will be crucial. Herein, we described a transmission assay based on the use of phloem sap extracted from infected citrus plants and topical feeding to D. citri nymphs. Phloem sap was collected by centrifugation, diluted with 0.1 M phosphate buffer pH 7.4 containing 20% (wt/vol) sucrose and 0.1% ascorbic acid (wt/vol) as an antioxidant, and delivered to third through fifth instar nymphs by placing droplets on the mouthparts. Nymphs unfolded the stylets and acquired the phloem sap containing the bacterial pathogen. Nymphs were then placed onto Citrus macrophylla seedlings (10 nymphs per seedling) for an inoculation period of 2 weeks. A transmission rate of up to 80% was recorded at 6 months postinoculation. The method could be a powerful tool to test the transmissibility of the bacterial pathogen after various treatments to reduce the viability of the bacteria or to block its transmission. In addition, it might be a potent assay to achieve Koch's postulates if a pure culture of 'Ca. L. asiaticus' becomes available.

The southern corn leaf blight epidemic of 1970 caused estimated losses of about 16% for the U.S. corn crop, equivalent to about $8 billion in current terms. The epidemic was caused by the prevalence of Texas male sterile cytoplasm (cms-T), used to produce most of the hybrid corn seed planted that year, combined with the emergence of a novel race of the fungus Cochliobolus heterostrophus that was exquisitely virulent on cms-T corn. Remarkably, the epidemic lasted just a single year. This episode has often been portrayed in the literature and textbooks over the last 50 years as a catastrophic mistake perpetrated by corn breeders and seed companies of the time who did not understand or account for the dangers of crop genetic uniformity. In this perspective article, we aim to present an alternative interpretation of these events. First, we contend that, rather than being caused by a grievous error on the part of the corn breeding and seed industry, this epidemic was a particularly unfortunate, unusual, and unlucky consequence of a technological advancement intended to improve the efficiency of corn seed production for America's farmers. Second, we tell the story of the resolution of the epidemic as an example of timely, meticulously applied research in the public sector for the public good.