Characterization of Colletotrichum Isolates: Causal Agents of Postharvest Anthracnose Disease of Avocado cv. Hass in Myanmar

Abstract

Postharvest losses associated with anthracnose disease of avocado fruit have been studied in all avocado-growing countries in the world. In Myanmar, anthracnose is one of the most significant post-harvest diseases affecting avocado fruits; however, the causal agent of this disease remains unidentified. This study aimed to determine the fungal pathogen that causes anthracnose disease in the avocado cv. Hass through pathogenicity test, morphological characterization, and molecular identification in Myanmar. Avocado fruits showing typical symptoms of anthracnose disease were collected from three commercial avocado orchards, Taunggyi, He Hoe in Southern Shan State, and Pyin Oo Lwin in Mandalay Region in Myanmar. Three Colletotrichum isolates were obtained, namely TG, POL, and HH. In the pathogenicity test, all isolates were pathogenic. The TG Colletotrichum isolate showed the most virulent pathogenicity, indicated by the largest lesion diameter (4.06±0.15 cm among all isolates (2.35±0.19 and 2.25±0.18 cm for POL and HH, respectively). Based on the cultural characterization, these three isolates were morphologically identified as Colletotrichum spp. They were primarily whitish to greyish in color, with a white-to-black circular zone on the reverse side and a cottony, fluffy texture on the upper side. The shape of conidia was cylindrical and straight with rounded ends. The mycelial growth rate of the TG isolate is 11.92±0.32 mmday-1 and significantly different from other isolates, POL and HH (9.83±0.24,10.60±0.24mmday-1) respectively. In the molecular identification, all isolates were identified as C. gloeosporioides using ITS4, species-specific primers CgInt for C.gloeosporioides and CaInt for C. acutatum. This study investigated that this is the first report of C.gloeosporioides causing postharvest anthracnose disease in avocado cv. Hass in Myanmar.