Abstract
Cyclocarya paliurus is an extremely valuable and multifunctional tree species whose leaves have traditionally been used in used in medicine or as a medicinal tea in China. In recent years, anthracnose has been frequently observed on young leaves of C. paliurus in several nurseries located in Jiangsu Province, resulting in great yield and quality losses. To date, no information is available about the prevalence of C. paliurus anthracnose in China. The main purpose of the present study was to characterize the etiology of C. paliurus anthracnose. Phylogenetic analysis of the eight-loci concatenated dataset revealed that all 44 single-spore Colletotrichum isolates belonged to three species in the Colletotrichum gloeosporioides species complex, namely, Colletotrichum aenigma, Colletotrichum fructicola, and C. gloeosporioides sensu stricto. Phenotypic features, including the colony appearance and the morphology of conidia, appressoria, and ascospores, were consistent with the phylogenetic grouping. Virulence tests validated that the three Colletotrichum species could cause typical symptoms of anthracnose on C. paliurus leaves, similar to those observed in the field. The optimum mycelial growth temperature ranged from 25 to 30°C for all representative isolates, while C. gloeosporioides s. s. isolates exhibited greater tolerance to high temperature (40°C). Fungicide sensitivity assays indicated that all three Colletotrichum species were sensitive to tetramycin, which may be a potential alternative for the management of C. paliurus anthracnose. To our knowledge, this study provides the first report of C. aenigma, C. fructicola, and C. gloeosporioides s. s. causing C. paliurus anthracnose in China as well as in the world.
Highlights
Cultivated for fine timber and as a medicinal plant, Cyclocarya paliurus is the sole extant species in the genus Cyclocarya and is native to China, naturally distributed in mountainous regions in the middle and lower reaches of the Yangtze River (Fang et al, 2011; Deng et al, 2015; Xie et al, 2015; Zheng et al, 2020)
Field Symptoms and Colletotrichum Isolates In May 2018, typical symptoms of anthracnose were first observed on newly emerged leaves of C. paliurus in a commercial nursery in Baima (Figure 1A), and the infection quickly spread to all C. paliurus nurseries within the growing season, with the infection rate reaching 64% (150 trees were investigated)
The cultivation of C. paliurus has undergone a major expansion to meet the increasing demand for young leaves of this species for medical use or C. paliurus tea production in China, which may have caused the high incidence of foliar diseases in these newly established plantations
Summary
Cultivated for fine timber and as a medicinal plant, Cyclocarya paliurus is the sole extant species in the genus Cyclocarya and is native to China, naturally distributed in mountainous regions in the middle and lower reaches of the Yangtze River (Fang et al, 2011; Deng et al, 2015; Xie et al, 2015; Zheng et al, 2020). The Coelomycetous genus Colletotrichum Corda includes plant pathogens responsible for anthracnose diseases with a global distribution (Hyde et al, 2009; Wikee et al, 2011; Cannon et al, 2012; Dean et al, 2012; He et al, 2019). The majority of studies regarding anthracnose were conducted principally via morphology and multigene phylogeny based on modern taxonomic concepts, which provides a more precise and robust solution (Damm et al, 2012; Liu et al, 2014, 2015; De Silva et al, 2017a; Diao et al, 2017; Guarnaccia et al, 2017; Fu et al, 2019)
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