Phytopathology最新文献

Barley grass (Hordeum leporinum), which often occurs in proximity to commercial barley (H. vulgare) cultivars, is an alternative host to Pyrenophora teres, an economically important pathogen causing net blotch in barley. This study is the first to report the sexual recombination of P. teres isolates collected from barley with those collected from barley grass. The sexual recombination between P. teres isolates from barley and barley grass was confirmed using a neighbor-net network and haploblock plots based on whole-genome sequencing of seven progeny isolates. Pathogenicity assays revealed that P. teres isolates from barley grass were not host specific and could infect both barley and barley grass, and the progeny isolates were virulent on commercially grown barley cultivars. Our results contradict previous population and pathogenicity studies of P. teres isolates obtained from barley and barley grass that have reported that the two populations are genetically distinct and host specific, suggesting that isolates collected from barley or barley grass could be two different entities. Despite the genetic divergence of P. teres isolates from barley and barley grass revealed through our phylogenomic analysis, there seems to be no complete host or reproductive separation between these populations. Therefore, there is a potential for generation of novel pathotypes through sexual recombination between P. teres isolates associated with barley and barley grass, with a risk of increased impacts on commercial barley cultivars that do not carry resistance to these pathotypes.

A protein-expressing citrus tristeza virus-based vector construct, pT36CA-V1.3, obtained from a California isolate of the T36 strain (T36CA), was retooled into a virus-induced gene silencing system intended for use with studies of California citrus. Virus-induced gene silencing constructs engineered with a truncated Citrus macrophylla PHYTOENE DESATURASE (CmPDS) gene sequence in the sense or antisense orientation worked equally well to silence the endogenous CmPDS gene. In a parallel effort to optimize vector performance, two nonsynonymous nucleotides in open reading frame 1a of pT36CA-V1.3 were replaced with those conserved in the reference sequences from the T36CA cDNA library. The resulting viruses, T36CA-V1.4 (with one amino acid modification: D760N) and T36CA-V1.5 (with two amino acid modifications: D760N and P1174L), along with T36CA-V1.3, were individually propagated in Nicotiana benthamiana and C. macrophylla plants. Enzyme-linked immunosorbent assay (ELISA) measurements of extracts of the newly emerged leaves suggested that all three viruses accumulated to similar levels in N. benthamiana plants at 5 weeks postinoculation. ELISA values of T36CA-V1.4- and -V1.5-infected C. macrophylla samples were significantly higher than that of T36CA-V1.3-infected samples within an 8- to 12-month postinoculation window, suggesting a higher accumulation of T36CA-V1.4 and -V1.5 than T36CA-V1.3. However, at 36 months postinoculation, the ELISA values suggested that all three viruses accumulated to similar levels. When C. macrophylla plants infected with each of the three viruses were grafted to commercial citrus varieties, a limited number of receptor plants became infected, demonstrating a weak but nonetheless (the first) successful delivery of T36CA to California-grown commercial citrus.

Moko disease in banana is a bacterial wilt caused by strains within Ralstonia solanacearum sensu stricto. The disease is endemic to Central and South America but has spread to the Philippines and peninsular Malaysia. Detecting new incursions early in Moko-free banana production regions is of utmost importance for containment and eradication, as Moko management significantly increases costs in banana production. Molecular studies have supported the classification of R. solanacearum sensu stricto into phylotypes IIA, IIB, and IIC, each comprising various sequevars based on nucleotide divergence of a partial sequence within the endoglucanase gene. Moko disease in banana is caused by strains classified as sequevars 6, 24, 41, and 53 within phylotype IIA and sequevars 3, 4, and 25 within phylotype IIB. To ensure accurate diagnostic assays are available to detect all Moko sequevars, we systematically validated previously published assays for Moko diagnostics. To be able to identify all sequevars, including the latest described sequevars, namely IIB-25, IIA-41, and IIA-53, we developed and validated two novel assays using genome-wide association studies on over 100 genomes of R. solanacearum sensu stricto. Validations using 196 bacterial isolates confirmed that a previous multiplex PCR-based assay targeting sequevars IIB-3, IIB-4, IIA-6, and IIA-24 and our two novel assays targeting sequevars IIB-25, IIA-41, and IIA-53 were specific, reproducible, and accurate for Moko diagnostics.

4'-Phosphopantetheinyl transferases (PPTases) play important roles in the posttranslational modifications of bacterial carrier proteins, which are involved in various metabolic pathways. Here, we found that RsacpS and RspcpS encoded a functional AcpS-type and Sfp-type PPTase, respectively, in Ralstonia solanacearum GMI1000, and both are capable of modifying R. solanacearum AcpP1, AcpP2, AcpP3, and AcpP5 proteins. RspcpS is located on the megaplasmid, which does not affect strain growth and fatty acid synthesis but significantly contributes to the virulence of R. solanacearum and preferentially participates in secondary metabolism. We found that deletion of RspcpS did not affect the abilities of cellulose degradation, biofilm formation, and resistance to NaCl, sodium dodecyl sulfate, and H₂O₂ and attenuated R. solanacearum pathogenicity only in the assay of soil-drenching infection but not stem injection of tomato. It is hypothesized that RsPcpS plays a role in cell viability in complex environments and in the process during which the strain recognizes and approaches plants. These results suggest that both RsAcpS and RsPcpS may be potential targets for controlling diseases caused by R. solanacearum.

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae is one of the epidemic diseases in rice. Rapid changes in the pathogenicity of the X. oryzae pv. oryzae pathogen demand the identification and characterization of novel BB resistance genes. Here, we report the transfer and mapping of a new BB resistance gene from Oryza rufipogon acc. CR100098A. Inheritance studies on the BC₂F₂ population, BC₂F₃ progenies, and backcross-derived recombinant inbred lines derived from a cross between Pusa44/O. rufipogon acc. CR100098A//2^*PR114 showed that a single recessive gene confers resistance in O. rufipogon acc. CR100098A. Bulked segregant analysis using 203 simple sequence repeat (SSR) markers localized the BB resistance gene on chromosome 11 bracketed between two SSR markers, RM27235 and RM2136. Using PR114 and O. rufipogon acc. CR100098A genotyping by sequencing data, 86 KASP markers within the bracketed region were designed and tested for bulked segregant analysis. Only five KASP markers showed polymorphism between parents, and three were associated with the target gene. Seventy-seven new SSR markers were designed from the same interval. A total of 33 polymorphic markers were analyzed on the whole population and mapped the BB gene in an interval of 2.8 cM flanked by SSR markers PAU11_65 and PAU11_44 within a physical distance of 376.3 kb. The BB resistance gene mapped in this study is putatively new and designated as xa49(t). Fourteen putative candidate genes were identified within the xa49(t) region having a role in biotic stress resistance. The linked markers to the xa49(t) gene were validated in other rice cultivars for its successful deployment in BB resistance breeding.

Dollar spot is a destructive foliar disease of amenity turfgrass caused by Clarireedia spp. fungi, mainly C. jacksonii, on the Northern United States region's cool-season grass. Oxalic acid (OA) is an important pathogenicity factor in related fungal plant pathogens such as Sclerotinia sclerotiorum; however, the role of OA in the pathogenic development of C. jacksonii remains unclear due to its recalcitrance to genetic manipulation. To overcome these challenges, a CRISPR/Cas9-mediated homologous recombination approach was developed. Using this novel approach, the oxaloacetate acetylhydrolase (oah) gene that is required for the biosynthesis of OA was deleted from a C. jacksonii wild-type (WT) strain. Two independent knockout mutants, ΔCjoah-1 and ΔCjoah-2, were generated and inoculated on potted creeping bentgrass along with a WT isolate and a genome sequenced isolate LWC-10. After 12 days, bentgrass inoculated with the mutants ΔCjoah-1 and ΔCjoah-2 exhibited 59.41% lower dollar spot severity compared with the WT and LWC-10 isolates. OA production and environmental acidification were significantly reduced in both mutants when compared with the WT and LWC-10. Surprisingly, stromal formation was also severely undermined in the mutants in vitro, suggesting a critical developmental role of OA independent of plant infection. These results demonstrate that OA plays a significant role in C. jacksonii virulence and provide novel directions for future management of dollar spot. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

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 to be 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 and the neomycin phosphotransferase 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 five plants co-infected by PRSV and PLDMV), and 56 (45.5%) 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%). However, overall, whether plants were transgenic or not made no difference to 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 geographic 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.

The image-based detection and classification of plant diseases has become increasingly important to the development of precision agriculture. We consider the case of tomato, a high-value crop supporting the livelihoods of many farmers around the world. Many biotic and abiotic plant health issues impede the efficient production of this crop, and laboratory-based diagnostics are inaccessible in many remote regions. Early detection of these plant health issues is essential for efficient and accurate response, prompting exploration of alternatives for field detection. Considering the availability of low-cost smartphones, artificial intelligence-based classification facilitated by mobile phone imagery can be a practical option. This study introduces a smartphone-attachable 30× microscopic lens, used to produce the novel tomato microimaging data set of 8,500 images representing 34 tomato plant conditions on the upper and lower sides of leaves as well as on the surface of tomato fruits. We introduce TOMMicroNet, a 14-layer convolutional neural network (CNN) trained to classify biotic and abiotic plant health issues, and we compare it against six existing pretrained CNN models. We compared two separate pipelines of grouping data for training TOMMicroNet, either presenting all data at once or separating the data into subsets based on the three parts of the plant. Comparing configurations based on cross-validation and F1 scores, we determined that TOMMicroNet attained the highest performance when trained on the complete data set, with 95% classification accuracy on both training and external data sets. Given TOMMicroNet's capabilities when presented with unfamiliar data, this approach has potential for the identification of plant health issues.

Passifloraceae is a plant family that includes several species of interest in the food, medicinal, and ornamental industries. The most relevant species are the purple and yellow varieties of P. edulis, which are among the most highly prized tropical fruits in the international markets. Unfortunately, the rapid expansion of this crop worldwide has resulted in the emergence of several viral diseases that endangered the productivity of this crop. In this work, we performed an integrated analysis of the Passifloraceae virome using public data. We investigated Pubmed and Genbank records and analyzed all the transcriptome data available for members of this plant family. This analysis resulted in the identification of six novel virus associations and six putative new viral species. We also used RNAseq to inspect virus accumulation levels and mixed infections. Using network analysis, we also examined the global distribution of Passiflora viruses and their associations with alternative hosts, which is valuable information in implementing viral disease management strategies. Our data suggest that a large diversity of viruses remains to be discovered. Finally, we used the information gathered in this work to estimate the cross-transmission risk of viruses in Colombian Passiflora fields.