Search

Identifying sources of phytopathogen inoculum and determining their contributions to disease outbreaks are essential for predicting disease development and establishing control strategies. Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust, is an airborne fungal pathogen with rapid virulence variation that threatens wheat production through its long-distance migration. Because of wide variation in geographic features, climatic conditions, and wheat production systems, Pst sources and related dispersal routes in China are largely unclear. In the present study, we performed genomic analyses of 154 Pst isolates from all major wheat-growing regions in China to determine Pst population structure and diversity. Through trajectory tracking, historical migration studies, genetic introgression analyses, and field surveys, we investigated Pst sources and their contributions to wheat stripe rust epidemics. We identified Longnan, the Himalayan region, and the Guizhou Plateau, which contain the highest population genetic diversities, as the Pst sources in China. Pst from Longnan disseminates mainly to eastern Liupan Mountain, the Sichuan Basin, and eastern Qinghai; that from the Himalayan region spreads mainly to the Sichuan Basin and eastern Qinghai; and that from the Guizhou Plateau migrates mainly to the Sichuan Basin and the Central Plain. These findings improve our current understanding of wheat stripe rust epidemics in China and emphasize the need for managing stripe rust on a national scale., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Colletotrichum siamense was demonstrated as the dominant species among Colletotrichum spp. that infected rubber tree, areca palm, and coffee in Hainan, China. However, the extent of genetic differentiation within the species C. siamense in relation to geographical regions and host species is not known. In this study, 112 C. siamense isolates were genotyped with 12 microsatellite markers. In total, there were 99 multilocus genotypes. Results from permutational multivariate analysis of variance and analysis of molecular variance indicated that there was no significant genetic differentiation between fungal populations with respect to host, location (county), and year. Discriminant analysis of principal components and STRUCTURE analysis showed that C. siamense isolates grouped into three clusters; further analysis confirmed that there were significant ( P < 0.001) genetic differences among the three clusters. However, each cluster had isolates from different hosts, counties, or years, supporting the lack of genetic differentiation with respect to host, county, and year. Statistical analyses of allelic associations indicated some evidence for recombination within the populations defined on the basis of host or county. The present findings provide insights into the genetic structure of C. siamense on the three perennial host species in Hainan and suggest that the disease on these three crops can be effectively considered as one disease and, hence, needs to be controlled simultaneously in mixed plantations.

Strawberry anthracnose caused by Colletotrichum spp. is one of the most serious diseases in the strawberry fields of China. In total, 196 isolates of Colletotrichum were obtained from leaves, stolons, and crowns of strawberry plants with anthracnose symptoms in eastern China and were characterized based on morphology, internal transcribed spacer (ITS), and β- tubulin ( TUB2 ) gene sequences. All 196 isolates were identified as the Colletotrichum gloeosporioides species complex. In total, 62 strains were further identified at the species level by phylogenetic analyses of multilocus sequences of ITS, glyceraldehyde-3-phosphate dehydrogenase ( GAPDH ), actin ( ACT ), Apn2-Mat1-2 intergenic spacer and partial mating type ( ApMat ), calmodulin ( CAL ), and TUB2 . Three species from the C. gloeosporioides species complex were identified: Colletotrichum siamense , C . fructicola , and C . aenigma . Isolates of C . siamense were tolerant to high temperatures, with a significantly larger colony diameter than the other two species when grown above 36°C. The inoculation of strawberry plants confirmed the pathogenicity of all three species. C . siamense isolates resulted in the highest disease severity. The in vitro sensitivities of C . siamense and C . fructicola isolates to azoxystrobin and three demethylation-inhibitor (DMI) fungicides (difenoconazole, tebuconazole, and prochloraz) were determined. Both species were sensitive to DMI fungicides but not to azoxystrobin. C . siamense isolates were more sensitive to prochloraz, while C. fructicola isolates were more sensitive to difenoconazole and tebuconazole. The present study provides valuable information for the effective management of strawberry anthracnose.

Genus Colletotrichum is one of the most important genera of plant-pathogenic fungi affecting numerous species, particularly tropical and subtropical crops and fruit trees. In this study, 43 Colletotrichum strains were isolated from areca palm leaves with anthracnose symptoms in 11 areca palm plantations in eight counties of Hainan, China. Based on the morphology, phylogenetic analysis of six loci (internal transcribed spacer, actin, chitin synthase 1, glyceraldehyde-3-phosphate dehydrogenase, β-tubulin, and mating type locus MAT1-2), and pathogenicity tests, eight Colletotrichum species were distinguished, comprising five previously known species ( C. cordylinicola , C. fructicola , C. gloeosporioides , C. siamense , and C. tropicale ), one unidentified Colletotrichum species, a new species ( C. arecicola ) in the gloeosporioides species complex, and C. karstii in the boninense species complex. C. siamense was the most common species found in areca palm in Hainan, followed by C. arecicola . Pathogenicity tests showed that all eight species could cause anthracnose symptoms on areca palm leaves using a wound inoculation method and that the isolates from the gloeosporioides species complex caused larger lesions than the isolates from the boninense species complex. Further research is needed to understand the epidemiology of these pathogenic species on areca palm in order to develop management strategies.

Verticillium dahliae is a widely distributed soilborne pathogen that causes vascular wilt in more than 200 plant species. Defoliating and nondefoliating symptoms caused by the disease that result in either the loss or retention of leaves in infected plants, respectively, in hosts such as cotton, olive, and okra, divide the causal agent into defoliating and nondefoliating pathotypes. Our goal in this current work was to generate genome resources for the defoliating strain XJ592 and the nondefoliating strain XJ511 of V. dahliae isolated from cotton in China.

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss. ( Pst ), is an important disease of wheat. In China, Pst management has focused on the Gansu region where the pathogen can complete its annual cycle, including oversummering and overwintering. From this region, Pst inoculum is dispersed to the southern Yangtze River region in the late autumn/early winter and then to the main wheat production regions in the following spring. We used historical weather data (1995 to 2016) and field stripe rust assessment data (8 years) in the spring to evaluate the performance of a published model for predicting the potential of Pst overwintering in the Gansu region. Both predicted and observed values of rust overwintering in the Gansu region varied greatly between years and between sites within a single year, indicating the value of predicting rust overwintering for disease management. The model predictions fitted with observed values satisfactorily. All high incidences of rust in the spring were observed in the fields of the monitoring sites where the high potential of overwintering was predicted. Conversely, the predicted rust overwintering potential was also close to zero in the fields where rust was not observed in the spring. There were many false-positive predictions, which may be attributable to the absence of rust in autumn seedlings. This model can be used to target rust management in the spring and its effectiveness will be further improved if autumn rust assessment can be carried out.

Stripe rust, caused by Puccinia striiformis f. sp. tritici Erikss., is an important disease of wheat worldwide. Identification of pathogen survival hot spots is important for predicting disease onset and subsequent spread to other regions, and such understanding is essential for developing integrated management strategies. We conducted field studies to determine the relationship of P. striiformis f. sp. tritici overwintering potential to winter temperatures in 10 sites in the northwest of China in three growing seasons (2011-12, 2012-13, and 2013-14). The fungus survived better in wheat cultivars with stronger winter hardiness than in those with weaker winter hardiness. Windowpane analysis suggested that P. striiformis f. sp. tritici winter survival is related to temperatures in the coldest period from mid-December to late January. β Regression showed that P. striiformis f. sp. tritici winter survival was negatively related to the number of days with daily average temperature <-2°C for cultivars with weak winter hardiness and <-4°C for cultivars with both moderate and strong winter hardiness. Models developed under constant temperature experiments greatly underestimate the P. striiformis f. sp. tritici overwinter potential under field conditions. This underestimation probably results from the possibility that P. striiformis f. sp. tritici in wheat tissues may have increased tolerance to low temperatures because of acclimation to gradual temperature changes under field conditions. The present models can be used to predict quantitative risks of P. striiformis f. sp. tritici overwintering in winter-wheat-growing regions for timely implementation of regional disease management strategies.

Colletotrichum gloeosporioides and C. acutatum have been reported to be causal agents of anthracnose disease of rubber tree. Recent investigations have shown that both C. gloeosporioides and C. acutatum are species complexes. The identities of Colletotrichum species causing anthracnose disease of rubber tree in Hainan, China, are unknown. In this study, 106 isolates obtained from rubber tree with symptoms of anthracnose were collected from 12 counties of Hainan and identified at the species complex level based on the ITS sequences and colony morphologies. Seventy-four isolates were identified as C. gloeosporioides species complex and the other 32 isolates as C. acutatum species complex. Forty-two isolates were selected for further multilocus phylogenetic analyses in order to identify the isolates to the species level. Twenty-six isolates from the C. gloeosporioides species complex were characterized for partial sequences of seven gene regions (ACT, TUB2, CHS-1, GAPDH, ITS, ApMat, and GS), and the other 16 isolates from the C. acutatum species complex for five gene regions (ACT, TUB2, CHS-1, GAPDH, and ITS). Three species were identified: C. siamense and C. fructicola from the C. gloeosporioides species complex, and a new species C. wanningense from the C. acutatum species complex. Artificial inoculation of rubber tree leaves confirmed the pathogenicity of the three species. The present study improves the understanding of species causing anthracnose on rubber tree and provides useful information for the effective control of the disease.