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Litchi (Litchi chinensis) is an evergreen fruit tree grown in subtropical and tropical countries. China accounts for 71.5% of the total litchi cultivated area in the world. Anthracnose disease caused by Colletotrichum species is one of the most important diseases of litchi in China. In this study, the causal pathogens of litchi anthracnose in Hainan, China, were determined using phylogenetic and morphological analyses. The results identified eight Colletotrichum species from four species complexes, including a proposed new species. These were C. karsti from the C. boninense species complex; C. gigasporum and the proposed new species C. danzhouense from the C. gigasporum species complex; C. arecicola, C. fructicola species complex; C. arecicola, C. fructicola and C. siamense from the C. gloeosporioides species complex; and C. musicola and C. plurivorum from the C. orchidearum species complex. Pathogenicity tests showed that all eight species could infect litchi leaves using a wound inoculation method, although the pathogenicity was different in different species. To the best of our knowledge, the present study is the first report that identifies C. arecicola, C. danzhouense, C. gigasporum and C. musicola as etiological agents of litchi anthracnose. [ABSTRACT FROM AUTHOR]

Black pepper (Piper nigrum L.) is one of the most ancient spice crops in the world. Hainan Province is the largest black pepper‐producing region in China. Viral disease is one of the main factors affecting black pepper. However, there are rarely studies on black pepper viral disease in China. We performed a survey in five major black pepper‐growing counties (Qionghai, Wenchang, Wanning, Haikou and Ding'an) of Hainan Province and collected 589 samples, with virus‐like symptoms from 2014 to 2019. Various viruses were identified including cucumber mosaic virus (CMV), piper yellow mottle virus (PYMoV), Piper DNA virus 1 (PDV‐1) and Piper DNA virus 2 (PDV‐2) using small RNA deep sequencing. The RT‐PCR screening of field samples indicated three types of infection: CMV alone (5.56%), PYMoV + PDV‐1 + PDV‐2 (25.00%) and PYMoV + CMV +PDV‐1 + PDV‐2 (69.44%). The data suggested that PYMoV might be the main pathogen causing virus diseases of black pepper. Two complete genome sequences of PYMoV were obtained. Phylogenetic analysis showed that PYMoV isolates from China were placed in a branch distinct from PYMoV isolates from India. To our knowledge, this is the first report of PYMoV, PDV‐1 and PDV‐2 naturally infecting black pepper, and the first genome sequence of PYMoV in China. [ABSTRACT FROM AUTHOR]

Phytoplasmas are a group of plant prokaryotic pathogens distributed worldwide. To comprehensively reveal the diversity of the pathogens and the diseases they cause on Hainan, a tropical island with abundant biodiversity in China, a survey of phytoplasmal diseases was performed from 2009 to 2022. Herein, molecular identification and genetic analysis were conducted based on the conserved genes of phytoplasmas. The results indicated that phytoplasmas could be detected in 138 samples from 18 host plants among 215 samples suspected to be infected by the pathogens. The phytoplasma strains from 27 diseased samples of 4 host plants belonged to the 16SrI group and the strains from 111 samples of 14 hosts belonged to the 16SrII group. Among them, 12 plants, including important tropical cash crops such as Phoenix dactylifera , cassava, sugarcane, and Piper nigrum , were first identified as hosts of phytoplasmas on Hainan Island. Based on BLAST and i PhyClassifier analyses, seven novel 16Sr subgroups were proposed to describe the relevant phytoplasma strains, comprising the 16SrI-AP, 16SrI-AQ, and 16SrI-AR subgroups within the 16SrI group and the 16SrII-Y, 16SrII-Z, 16SrII-AB, and 16SrII-AC subgroups within the 16SrII group. Genetic variation and phylogenetic analysis indicated that the phytoplasma strains identified in this study and those reported previously on Hainan Island mainly belong to four 16Sr groups (including I, II, V, and XXXII) and could infect 44 host plants, among which the 16SrI and 16SrII groups were the prevalent 16Sr groups associated with 43 host plant species. The diversity of host plants infected by the phytoplasmas made it difficult to monitor and control their related diseases. Therefore, strengthening inspection and quarantine during the introduction and transit of the related phytoplasmal host crops would effectively curb the spread and prevalence of the phytoplasmas and their related lethal diseases., Competing Interests: The author(s) declare no conflict of interest.

In order to manage agricultural pathogens, it is crucial to understand the population structure underlying epidemics. Rubber tree powdery mildew, caused by Erysiphe quercicola , is a serious threat to rubber plantations worldwide, especially in subtropical environments including all rubber tree-growing regions in China. However, the population structure of the pathogen is uncertain. In this study, 16 polymorphic microsatellite markers were used to genotype powdery mildew samples from the main rubber tree-growing regions including Yunnan (YN), Hainan (HN), western Guangdong (WG), and eastern Guangdong (EG). YN had higher genotypic diversity (Simpson's indices), genotypic evenness, Nei's gene diversity, allelic richness, and private allelic richness than the other regions. Cluster analysis, discriminant analysis of principal components, pairwise divergence, and shared multilocus genotype analyses all showed that YN differed significantly from the other regions. The genetic differentiation was small among the other three regions (HN, WG, and EG). Analysis of molecular variance indicated that the variability among regions accounted for 22.37% of the total variability. Genetic differentiation was significantly positively correlated ( R xy = 0.772, P = 0.001) with geographic distance. Linkage equilibrium analysis suggested possible occurrence of sexual recombination although asexual reproduction predominates in E. quercicola . The results suggested that although significant genetic differentiation of E. quercicola occurred between YN and the other regions, pathogen populations from the other three regions lacked genetic differentiation., Competing Interests: The author(s) declare no conflict of interest.

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.

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.

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.

Colletotrichum gloeosporioides and C. acutatum species complexes are causal agents of Colletotrichum leaf disease (CLD) of rubber trees worldwide. To determine the geographic distribution of Colletotrichum species complexes associated with CLD of rubber trees in Hainan, China, and their sensitivity to fungicides used in the region, a total of 275 Colletotrichum isolates were collected from 52 rubber tree plantations in 11 counties. These isolates were identified based jointly on morphological characteristics and PCR-based methodology. Of these isolates, 78 and 22% belonged to the C. gloeosporioides species complex (CGSC) and the C. acutatum complex (CASC), respectively. The incidence of CGSC isolates was greater than the CASC in all counties sampled. The incidence of CASC isolates appeared to be lower in the western and central south of Hainan than in other regions. There was no association in their presence at a given plantation between the two species complexes. The in vitro sensitivity of these two species complexes to carbendazim, chlorothalonil, and four demethylation inhibitor (DMI) fungicides (difenoconazole, propiconazole, myclobutanil, and prochloraz) was determined. Carbendazim was effective against CGSC but not against CASC with mean ED 50 values of 0.176 and 2.182 µg/ml, respectively. CASC isolates were more sensitive to difenoconazole, propiconazole, and myclobutanil (mean ED 50 values of 0.177, 0.129, and 1.424 µg/ml, respectively) than CGSC isolates (mean ED 50 values of 0.710, 0.348, and 3.496 µg/ml, respectively). Mean ED 50 values of CGSC against chlorothalonil and prochloraz were 173.341 and 0.035 µg/ml, respectively; corresponding values for CASC were 151.441 and 0.040 µg/ml. These results suggest that prochloraz, propiconazole, and difenoconazole are effective against both species complexes.

Powdery mildew is a highly destructive winter wheat pathogen in China. Since the causative agent is sensitive to changing weather conditions, we analyzed climatic records from regions with previous wheat powdery mildew epidemics (1970 to 2012) and investigated the long-term effects of climate change on the percent acreage (PA) of the disease. Then, using PA and the pathogen's temperature requirements, we constructed a multiregression model to predict changes in epidemics during the 2020s, 2050s, and 2080s under representative concentration pathways RCP2.6, RCP4.5, and RCP8.5. Mean monthly air temperature increased from 1970 to 2012, whereas hours of sunshine and relative humidity decreased (P < 0.001). Year-to-year temperature changes were negatively associated with those of PA during oversummering and late spring periods of disease epidemics, whereas positive relationships were noted for other periods, and year-to-year changes in relative humidity were correlated with PA changes in the early spring period of disease epidemics (P < 0.001). Our models also predicted that PA would increase less under RCP2.6 (14.43%) than under RCP4.5 (14.51%) by the 2020s but would be higher by the 2050s and 2080s and would increase least under RCP8.5 (14.37% by the 2020s). Powdery mildew will, thus, pose an even greater threat to China's winter wheat production in the future.