Pathogen identification and biological characteristics of sweet persimmon anthracnose causing by Colletotrichum species

Abstract:【Objective】In 2021, the spot blight and fruit drop of persimmon, which caused by Colletotrichum sp., seriously affected over 50% of Taiqiu persimmon trees in an orchard (ca. 0.8 hm2 ) near Yongkang city, Zhejiang province, China. These pathogens infected fruits, sepals and pedicle on the persimmon tree, and hastened their senescence. The fruit set rate would be reduced while the disease exacerbated in the field, which seriously affected the yield of persimmon. So far, anthracnose of sweet persimmon fruit is very serious in Zhejiang province. In order to clarify the Colletotrichum species of sweet persimmon anthracnose, biological characteristics and occurrence conditions, the experiment was undertaken, which can not only understand the occurrence of persimmon anthracnose and influence factors, but also provide ecological prevention and control measures for persimmon anthracnose. Furthermore, this research can provide epidemiological basis for sweet persimmon anthracnose and help to develop ecological prevention and control for the cultivation of sweet persimmon in Zhejiang province.【Methods】The purified strains were isolated from the typical disease samples collected from Yongkang city, Zhejiang province, China. The isolated data of Colletotrichum species were assembled and the isolationfrequency from every month was showed in our research. The symptoms, colony morphology and conidia size of the main pathogens were observed in preliminary identification. Pathogenicity was measured by direct inoculation and wounded inoculation in illumination incubator under the conditions of 25 ℃, 16 h Light and 8 h dark. Phylogenetic tree of Colletotrichum species based on the combined ITSACT-TUB2-GAPDH-CHS1 sequences of the representative isolates was constructed by maximum likelihood method and Bayesian probability method with MEGA 7 software and Bayesian software. Bayesian posterior probabilities (Bpp) were followed by the bootstrap values of ML on the nodes in the topology. Representative strains of different Colletotrichum species were used for testing their biological characteristics. The effects of different pH values, temperatures and light conditions on the mycelial growth rate and spore productions under solid cultivation were investigated. The experimental data were analyzed by Duncan’s new range test (DMRT) in SPSS software.【Results】Colletotrichum horii, C. siamense and C. fructicola were the main pathogens of persimmon. To our knowledge, C. siamense has not previously been reported as a pathogen of sweet persimmon. The results showed that the suitable temperature for mycelium growth and spore production of C. fructicola, C. horii and C. siamense were from 25 ℃ to 35 ℃, and 30 ℃ was the optimum sporulation temperature. The optimum sporulation temperature of C. horii was 25 ℃. When the temperature exceeded 35 ℃, the mycelium grew slowly. The optimal media for mycelium growth of C. siamense and C. fructicola were PDA, CMA and GA. The optimal media for spore production of C. fructicola was CA, and the optimal media for spore production of C. siamense was CMA. The optimal media for mycelium growth of C. horii were PDA and CA. The optimal media for spore production was OA. Three Colletotrichum species could grow on the medium of all pH values. The optimum pH values for mycelium growth and spore production of C. fructicola were 5 and 9. The optimum pH values for mycelium growth and spore production of C. siamense and C. horii were 9 and 10. There was no effect on the mycelial growth of 3 Colletotrichum species, but the differences in spore production among 3 Colletotrichum species were obvious. Continuous light was beneficial to the sporulation of C. fructicola, and the sporulation of C. horii would be stimulated under the cultural condition of alternating dark and light. Light had little effect on the sporulation of C. siamensis. The lethal temperature of the conidia of C. fructicola was 47.9 ℃ for 10 min, and that of C. horii and C. siamensis was 49.2 ℃ for 10 min.【Conclusion】The result indicated that C. horii, C. siamense and C. fructicola were the main pathogens of sweet persimmon and they were clarified by the investigation and identification of sweet persimmon anthrax in Yongkang, Zhejiang province of China. Among them, the spot blight of persimmon caused by C. siamense was the first reported in China. According to the biological characteristics, the optimum culture temperature, pH value, light condition and spore death temperature of C. horii, C. siamense and C. fructicola of sweet persimmon were compared in the research so as to provide a scientific basis for ecological control of sweet persimmon anthrax.