Isolation and potential biocontrol of the fungus causing anthracnose in longan in Vietnam

Longan is a crop plant of very high economic value, and both its fruit and flower are beneficial for human health. Longan has been increasingly cultivated in Vietnam due to the increasing demand for domestic consumption as well as export of its fruit. However, the widespread emergence and spread of anthracnose, a group of fungal disease affecting a wide range of plant species, in longan has seriously affected both the longan fruit yield and quality in Vietnam. Current methods for the prevention of anthracnose in longan depend mainly on the use of fungicides which are very harmful to human health as well as disruptive to microbial community structures in different ecosystems. In order to obtain an environmentally friendly method of control for this disease, the agent causing anthracnose in longan must first be identified. Therefore, the aim of this study was to isolate and identify the causal anthracnose agent in longan in Vietnam. Methods: Experiments were first carried out with pieces of anthracnose longan leaves pressed onto the surface of potato-dextrose agar (PDA) and incubated for days at 30◦C. Colonies, varying in appearance, were repeatedly isolated and purified on PDA agar, and the anthracnose-causing agent was initially recognized on the basis of colony characteristics and cell morphology. The suspected isolate was then tested for its ability to decompose healthy longan leaf in vitro, and its rDNA region was cloned and sequenced to determine its taxonomy. Antifungal activity testing was performed using the co-culture method. Results: We obtained a fungal isolate with septate hyphae, ovoid appressoria, and conidia (which were cylindrical in shape with rounded ends). This isolate showed a clear ability to decompose healthy longan leaves. At the molecular level, the isolate was determined to be a fungal species belonging to genus Colletotrichum, and therefore named Colletotrichum sp. strain BKHCM. We also found that its growth was inhibited when co-cultured with Streptomyces flaveus, an actinomycete originating from soil. Conclusion: For the first time, we isolated a fungal species belonging to genus Colletotrichum from anthracnose-infected longan leaves in Vietnam. We also showed that the growth of this fungus could potentially be biocontrolled.