First Report of Phytopythium vexans Causing Stem and Leaf Necrosis on Rubber Tree (Hevea brasiliensis): Biological Characteristics and Fungicide Sensitivity
The findings provide a theoretical foundation for accurate disease diagnosis, epidemiological surveillance, and the development of effective chemical control strategies for rubber plantations.
Abstract
Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg., the world’s primary source of natural rubber, faces increasing threats from emerging diseases in tropical cultivation regions. During recent field surveys in Yunnan and Hainan provinces of China, previously uncharacterized brown, water-soaked necrotic lesions were observed on tender stems and leaves of rubber trees. This study aimed to identify the causal pathogen, characterize its biological traits, and evaluate candidate fungicides for disease management. The pathogen was isolated via tissue explant methods and identified through morphological observation combined with multigene phylogenetic analyses based on the internal transcribed spacer (ITS) region, large subunit (LSU) ribosomal DNA, and cytochrome c oxidase subunits I and II (coxI and coxII) sequences. Pathogenicity was rigorously confirmed by fulfilling Koch’s postulates on rubber tree seedlings. The isolates produced spherical to ovoid, papillate sporangia, and phylogenetic reconstruction strongly supported clustering them with Phytopythium vexans. The pathogen grew optimally at 16–31 °C, with growth ceasing at 35 °C. Fungicide sensitivity assays revealed that metalaxyl exhibited the strongest inhibitory activity against mycelial growth, with half-maximal effective concentration (EC50) values as low as 0.04 μg/mL. To our knowledge, this is the first report of P. vexans causing foliar and stem necrosis on H. brasiliensis. These findings provide a theoretical foundation for accurate disease diagnosis, epidemiological surveillance, and the development of effective chemical control strategies for rubber plantations.
Circular leaf spot disease (CLSD) has recently emerged as an important foliar disease of rubber (Hevea brasiliensis) in Viet Nam, yet information on its associated pathogens remains limited. This study investigated the biological characteristics and pathogenicity of Pestalotiopsis microspora and Colletotrichum siamense associated with CLSD. Sixteen isolates of each species were obtained from diseased leaves collected in major rubber-growing regions of Viet Nam. Morphological characteristics were evaluated on different culture media and temperature regimes, while pathogenicity was assessed under laboratory and greenhouse conditions and confirmed through Koch’s postulates. Pestalotiopsis microspora showed optimal growth on malt extract agar at 25°C, whereas C. siamense grew most rapidly on potato-based media at 25–30°C. ITS sequence analysis showed ≥99% similarity between all isolates and reference sequences of P. microspora and C. siamense in GenBank. Disease severity index values on detached leaves ranged from 34.4–52.1% for P. microspora, 54.5–99.8% for C. siamense, and 92.0–100% for mixed inoculations (ANOVA, p < 0.01). Greenhouse inoculations showed a similar pattern. Among six rubber clones, RRIV 124 was the most susceptible under laboratory conditions. These results indicate that CLSD in Viet Nam is associated with a pathogen complex in which C. siamense is more pathogenic than P. microspora, while...
Hieu Nguyen Don, Nhan Luan Doan, Thi Kim Uyen Nguyen· CTU Journal of Innovation an...· 0 citations
Durian (Durio zibethinus L.) is a high-value tropical fruit crop that has recently been cultivated on a commercial scale in Hainan Province, China. However, emerging diseases increasingly threaten sustainable production and fruit quality. Field surveys conducted in Sanya, Hainan, identified stem rot as the predominant disease affecting durian trees, with a disease incidence of approximately 26.6%. Affected trees exhibited necrotic lesions at stem-branch junctions, followed by leaf abscission and progressive decline. The causal agent was identified using morphological characteristics, phylogenetic analyses of the internal transcribed spacer (ITS) and translation elongation factor 1-alpha (TEF-1α) and RNA polymerase II second largest subunit (RPB2) gene regions, and pathogenicity assays. Inoculated plants developed symptoms consistent with those observed under field conditions, thereby fulfilling Koch’s postulates. Both morphological and multilocus molecular analyses consistently identified the pathogen as Fusarium solani. A total of 20 Fusarium isolates were obtained from diseased durian stem samples. To our knowledge, this is the first report of F. solani causing stem rot of durian in Hainan Province, China. In addition, Bacillus subtilis SYST2 exhibited strong antagonistic activity against F. solani isolates FS-1, FS-2, and FS-3 in vitro, with inhibition rates of 55.7%, 54.6%, and 53.3%, respectively. Field trials further demonstrated that application of SYST2 significantly suppressed disease development, achieving a biocontrol efficacy of 53.51%. These findings establish F. solani as a causal agent of durian stem rot in Hainan and highlight the potential of Bacillus-based biological control as a sustainable strategy for disease management in durian production systems.
Pholiota conissans is an economically important edible mushroom in China; however, its production has been severely impacted by cobweb disease during the fruiting stage, leading to substantial yield losses. In this study, a fungal pathogen was identified as the causal agent of cobweb disease. The strains were isolated from infected fruiting bodies collected in November 2021 and were identified as a new species Cladobotryum hypsigum sp. nov., based on morphological characteristics and a multi-locus phylogenetic analysis of four gene regions (ITS, RPB1, RPB2, and TEF). Pathogenicity tests were conducted by inoculating healthy mushrooms with a spore suspension of representative isolates. The resulting symptoms were consistent with those observed in cultivation settings, and the same pathogen was successfully re-isolated, thus fulfilling Koch's postulates. Biological characterization indicated that the optimal conditions for mycelial growth were a temperature of 25°C and pH 5. Sucrose and yeast extract were the most suitable carbon and nitrogen sources, respectively. In vitro fungicide sensitivity assays, performed using the hyphal growth inhibition method against six common fungicides, demonstrated that Carbendazim was the most effective agent. The IC50 values for Carbendazim were 0.7742 µg/mL for the pathogen and 4.827 µg/mL for the host mushroom, indicating significant selectivity. These findings provide a scientific basis for developing effective strategies to manage cobweb disease in P. conissans cultivation.
Fang Wu, Jing Tu, Zhu-Xiang Liu et al.· Plant Disease· 0 citations
Background Begonia fimbristipula, an economically important medicinal plant in southern China, has recently suffered severe yield losses from leaf spot disease in Guizhou and Hunan Provinces; the causal pathogen remains unknown. Methods Field surveys were conducted across multiple locations in Guizhou and Hunan Provinces to record disease symptoms and incidence. The pathogen was isolated from diseased leaves via tissue culture, and identified by combining morphological characteristics and multilocus phylogenetic analysis (ITS, TEF1α, RPB2). Pathogenicity was verified by fulfilling Koch’s postulates through artificial inoculation and re-isolation assays. Results Severe leaf spot outbreaks were observed in August 2024, with over 60% disease incidence across 667 hectares and >20% fresh leaf yield loss. The isolated pathogen was identified as Corynespora cassiicola based on gray to dark-gray colonies, pale-brown olivaceous conidia with 0–15 pseudosepta, and ≥98% bootstrap support in phylogenetic clustering with known C. cassiicola strains. Koch's postulates were fulfilled by reproducing typical field symptoms on inoculated B. fimbristipula seedlings and re-isolating the pathogen. Conclusions This is the first report of C. cassiicola causing leaf spot on B. fimbristipula in China, expanding the host range of this pathogen. Our findings provide a critical basis for the accurate diagnosis of this newly emerging disease on the medicinal plant.
Xiaobo Zhang, Xiaoyi Zuo, Jianhua Lu et al.· PLoS ONE· 0 citations
A previously unreported root rot and basal stem necrosis disease was observed in carnation (
Dianthus caryophyllus
) plants grown in greenhouses in Yalova Province, Türkiye, in 2018. A
Phytophthora
species was consistently isolated from symptomatic root and vascular tissues. Morphological examination revealed a heterothallic species with papillate, usually non‐caducous sporangia (sometimes with double papillae) having ovoid, obpyriform, ellipsoid or nearly spherical shapes, lateral attachment of sporangiophores and spherical chlamydospores in cultures. Mycelial growth on carrot agar occurred between 9.5°C and 31.5°C, with optimum growth at 25°C. Phylogenetic analyses performed using data from three nuclear (ITS, β‐tubulin and heat shock protein 90) and four mitochondrial regions (cytochrome c oxidase subunit 1, cytochrome c oxidase subunit 2, NADH dehydrogenase subunit 1 and ribosomal protein L10) placed isolates in a monophyletic subclade of
Phytophthora
Clade 2a, matching the recently described species
Phytophthora pseudocitrophthora
. Pathogenicity trials using soil with inoculated wheat grains showed that isolates induced main root rot and basal stem necroses consistent with field symptoms and significantly reducing root biomass in carnation seedlings within 3 months. All inoculated isolates were reisolated, fulfilling Koch's postulates. This study presents the first report of
P. pseudocitrophthora
causing disease in carnations and highlights its potential significance in ornamental plant pathology.
İ. Kurbetli, G. Sülü, S. Woodward et al.· Plant Pathology· 0 citations
Persimmon anthracnose is a major disease affecting fruit quality and yield in persimmon-growing regions, yet information on the species diversity of causal pathogens in Korea remains limited. This study aimed to identify Colletotrichum species associated with anthracnose symptoms on persimmon fruits and to evaluate their pathogenicity. Sixteen fungal isolates were obtained from symptomatic fruits collected pear research center in Naju, Korea, and their morphological characteristics—colony features, conidial morphology, and appressoria— were examined. Multilocus sequence analysis using internal transcribed spacer, actin, β-tubulin, glyceraldehyde-3-phosphate dehydrogenase, chitin synthase I, calmodulin, the intergenic spacer region between Apn2 and Mat1-2-1 (ApMat) was performed to determine species identity and phylogenetic relationships. Phylogenetic analysis revealed that most isolates (87.5%) belonged to Colletotrichum horii. One isolate each of C. siamense and C. fructicola were also identified; notably, C. fructicola represents the first report of this species on persimmon in Korea. Pathogenicity tests showed that all three species induced typical sunken lesions on wounded fruits, and the inoculated pathogens were successfully re-isolated, fulfilling Koch’s postulates. These findings demonstrate that persimmon anthracnose in Korea is caused by multiple Colletotrichum species with clear genetic differentiation. The detection of C. fructicola suggests that the species spectrum of anthracnose pathogens may be broader than previously recognized. This study provides essential baseline information for disease diagnosis, epidemiological monitoring, and the development of resistant cultivars in future breeding programs.
Hyegyoung Yoo, E. Choi, Mao Sopheap et al.· Research in Plant Disease· 0 citations