Phytopathology最新文献

The evolution of new variants of plant pathogens is one of the biggest challenges to controlling and managing plant diseases. Of the forces driving these evolutionary processes, global migration events are particularly important for widely distributed diseases such as potato late blight, caused by the oomycete Phytophthora infestans. However, little is known about its migration routes outside North America and Europe. This work used genotypic data from population studies to elucidate the migration history originating the Colombian P. infestans population. For this purpose, a dataset of 1,706 P. infestans genotypes was recollected, representing North and South America, Europe, and Asia. Descriptive analysis and historical records from North America and Europe were used to propose three global migration hypotheses, differing on the origin of the disease (Mexico or Peru) and the hypothesis that it returned to South America from Europe. These scenarios were tested using approximate Bayesian computation. According to this analysis, the most probable scenario (posterior probability = 0.631) was the one proposing a Peruvian origin for P. infestans, an initial migration toward Colombia and Mexico, and a later event from Mexico to the United States and then to Europe and Asia, with no return to northern South America. In Colombia, the scenario considering a single migration from Peru and posterior migrations within Colombia was the most probable, with a posterior probability of 0.640. The obtained results support the hypothesis of a Peruvian origin for P. infestans followed by rare colonization events worldwide.

Bacterial spot caused by Xanthomonas spp. is an economically important disease of pepper causing significant yield losses in Taiwan. Monitoring the pathogen population on a continuous basis is necessary for developing disease management strategies. We analyzed a collection of xanthomonad strains isolated from pepper in Taiwan between 1989 and 2019. Among the sequenced genomes, 65 were identified as Xanthomonas euvesicatoria, and 10 were X. perforans. Thirty-five X. euvesicatoria and 10 X. perforans strains were copper tolerant, whereas only four X. euvesicatoria and none of the X. perforans strains were tolerant to streptomycin. Nine X. euvesicatoria strains were amylolytic, which is considered an unusual characteristic for X. euvesicatoria. Bayesian analysis of the population structure based on core gene single-nucleotide polymorphisms clustered the strains into five clusters for X. euvesicatoria and three clusters for X. perforans. One X. perforans cluster, designated as TP-2019, appears to be a novel genetic cluster based on core genes, accessory gene content, and effector profile. This knowledge of pathogen diversity with whole genomic information will be useful in future comparative studies and in improving breeding programs to develop disease-resistant cultivars and other disease management options.

Fusarium head blight caused by Fusarium graminearum is a significant pathogen affecting wheat crops. During the infection process, effector proteins are secreted to modulate plant immunity and promote infection. The toxin deoxynivalenol is produced in infected wheat grains, posing a threat to human and animal health. Serine carboxypeptidases (SCPs) belong to the α/β hydrolase family of proteases and are widely distributed in plant and fungal vacuoles, as well as animal lysosomes. Research on SCPs mainly focuses on the isolation, purification, and production of a small number of fungi. The role of SCPs in plant secretion, growth and development, and stress resistance has also been extensively studied. However, their functions in F. graminearum, a fungal pathogen, remain relatively unknown. In this study, the biological functions of the FgSCP gene in F. graminearum were investigated. The study revealed that mutations in FgSCP affected the nutritional growth, sexual reproduction, and stress tolerance of F. graminearum. Furthermore, the deletion of FgSCP resulted in reduced pathogenicity and hindered the biosynthesis of deoxynivalenol. The upregulation of FgSCP expression 3 days after infection indicated its involvement in host invasion, possibly acting as a "smokescreen" to deceive the host and suppress the expression of host defensive genes. Subsequently, we confirmed the secretion ability of FgSCP and its ability to inhibit the cell death induced by INF1 in Nicotiana benthamiana cells, indicating its potential role as an effector protein in suppressing plant immune responses and promoting infection. In summary, we have identified FgSCP as an essential effector protein in F. graminearum, playing critical roles in growth, virulence, secondary metabolism, and host invasion.

Xanthomonas spp. are plant pathogens known for significantly impacting crop yields. Among them, Xanthomonas albilineans (Xal) is notable for colonizing the xylem and causing sugarcane leaf scald disease. This study employed homologous recombination to mutate quorum sensing (QS) regulatory genes (rpf) to investigate their role in Xal pathogenicity. Deletions of rpfF (ΔrpfF), rpfC (ΔrpfC), and rpfG (ΔrpfG) led to reduced swarming, growth, and virulence. However, DSF supplementation restored swarming and growth in the ΔrpfF mutant. Deleting rpfC, rpfG, and rpfF also reduced twitching motility and affected Type IV Pilus (T4P) expression. Transcriptomic analysis revealed that ΔrpfF positively regulates flagellar genes. DSF supplementation in ΔrpfF (ΔrpfF-DSF) modulated the expression of flagellar, chemotaxis, and T4P genes. These findings elucidate the DSF-mediated swarming pathway in Xal and provide valuable insights into its regulatory mechanisms.

Bacillus velezensis YL2021 has extensive antimicrobial activities against phytopathogens, and its genome harbors a catechol-type siderophore biosynthesis gene cluster. Here, we describe the characterization of siderophore produced by strain YL2021 and its antimicrobial activity in vitro and in vivo. A few types of siderophores were detected by chrome azurol S plates coupled with Arnow's test, purified and identified by Reversed-phase high-performance liquid chromatography (RP-HPLC). We found that strain YL2021 can produce different antimicrobial compounds under low-iron M9 medium or iron-sufficient LB medium although antimicrobial activities can be easily observed on the two media as described above in vitro. Strain YL2021 can produce at least three catechol-type siderophores in low-iron M9 medium while no siderophore was produced in LB medium. Among them, the main antimicrobial siderophore produced by strain YL2021 was bacillibactin, with m/z of 882, based on the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, which has broad-spectrum antimicrobial activities against Gram-positive, Gram-negative bacteria, the oomycete Phytophthora capsici and phytopathogenic fungi. Moreover, the antifungal activity of siderophore including bacillibactin observed in vitro was correlated with control efficacies against rice sheath blight disease caused by Rhizoctonia solani and rice blast disease caused by Magnaporthe oryzae in vivo. Collectively, the results demonstrate that siderophore including bacillibactin produced by Bacillus velezensis YL2021 is a promising biocontrol agent for application in rice disease control.

Most Ralstonia solanacearum species complex strains cause bacterial wilts in tropical or subtropical zones, but the group known as Race 3 biovar 2 (R3bv2) is cool virulent and causes potato brown rot at lower temperatures. R3bv2 has invaded potato-growing regions around the world but is not established in the United States. Phylogenetically, R3bv2 corresponds to a subset of the R. solanacearum phylotype IIB clade, but little is known about the distribution of the cool virulence phenotype within phylotype IIB. Therefore, genomes of 76 potentially cool virulent phylotype IIB strains and 30 public genomes were phylogenetically analyzed. A single clonal lineage within the sequevar 1 subclade of phylotype IIB that originated in South America has caused nearly all brown rot outbreaks worldwide. To correlate genotypes with relevant phenotypes, we quantified virulence of ten Ralstonia strains on tomato and potato at both 22°C and 28°C. Cool virulence on tomato did not predict cool virulence on potato. We found that cool virulence is a quantitative trait. Strains in the sequevar 1 pandemic clonal lineage caused the most disease, while other R3bv2 strains were only moderately cool virulent. However, some non-R3bv2 strains were highly cool virulent and aggressively colonized potato tubers. Thus, cool virulence is not consistently correlated with strains historically classified as R3bv2 group. To aid detection of sequevar 1 strains, this group was genomically delimited in the LINbase web server and a sequevar 1 diagnostic primer pair was developed and validated. We discuss implications of these results for the R3bv2 definition.

In soil-borne diseases, the plant-pathogen interaction begins as soon as the seed germinates and develops into a seedling. Aphanomyces euteiches, an oomycete, stays dormant in soil and gets activated by sensing the host through chemical signals present in the root exudates. The composition of plant exudates may, thus, play an important role during the early phase of infection. To better understand the role of root exudates in plant resistance, we investigated the interaction between partially resistant lines (PI660736 and PI557500) and susceptible pea cultivars (CDC Meadow and AAC Chrome) against Aphanomyces euteiches during the pre-invasion phase. The root exudates of two sets of cultivars clearly distinguished from each other in inducing oospore germination. PI557500 root exudate not only had diminished induction but also inhibited the oospore germination. The contrast between the root exudates of resistance and susceptible cultivars was reflected in their metabolic profiles. Data from fractionation and oospore germination inhibitory experiments identified a group of saponins that accumulated differentially in susceptible and resistant cultivars. We detected 56 saponins and quantified 44 of them in pea root and 30 from root exudate; the majority of them, especially Soyasaponin I and dehydrosoyasaponin I with potent in vitro inhibitory activities, were present in significantly higher amounts in both roots and root exudates of PI660736 and PI557500 as compared to Meadow and Chrome. Our results provide evidence for saponins as deterrents against Aphanomyces euteiches, which might have contributed to the resistance against root rot in the studied pea cultivars.

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 of banana production. Molecular studies have supported the classification of R. solanacearum sensu stricto into phylotypes IIA, IIB and IIC, each comprising of 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.

Verticillium dahliae is a soilborne phytopathogenic fungus causing Verticillium wilt on hundreds of plant species. Several sequenced genomes of V. dahliae are available, but functional characterization of most genes has just begun. Based on our previous comparison of the transcriptome from the wild-type and ΔVdCf2 strains, a significant upregulation of the gene cassette, Vd276-280, in the ΔVdCf2 strain was observed. In this study, the functional characterization of the Vd276-280 gene cassette was performed. Agrobacterium-mediated knockout of this gene cassette in V. dahliae significantly inhibited conidiation, melanized microsclerotium formation in the mutant strains, and their virulence towards cotton. Furthermore, deletion of individual genes in the Vd276-280 gene cassette identified that the disruption of VDAG_07276 and VDAG_07280 delayed microsclerotium formation, inhibited conidiation, and reduced virulence towards cotton. Our data suggest that VDAG_07276 and VDAG_07280 in the Vd276-280 gene cassette mainly act as positive regulators of development and virulence in V. dahliae.

Dollar spot is a destructive foliar disease of amenity turfgrass caused by the fungus Clarireedia spp., and mainly Clarireedia jacksonii on the northern US 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 C. jacksonii wild-type stain. Two independent knockout mutants, ΔCjoah-1 and ΔCjoah-2, were generated and inoculated on potted creeping bentgrass along with a wild-type isolate (WT) 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 to the WT and LWC-10 isolates. Oxalic acid production and environmental acidification were significantly reduced in both mutants when compared to 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.