Inhibition of Lasiodiplodia pseudotheobromae Causing Fruit Rot Disease of Longan by Using Antagonistic Bacillus siamensis RFCD306

P ostharvest fruit rot disease of longan (Dimocarpus longan Lour.) caused by Lasiodiplodia pseudotheobromae is one of the most devastating problems for longan production in Thailand. To reduce the use of chemicals, the endophytic bacterium was isolated from healthy longan fruit for using as a biological control agent. The antagonistic bacterium Bacillus siamensis isolate RFCD306 which was identified based on morphological, biochemical and molecular characterization. It showed the antifungal effect with 94.40% of fungal growth inhibition which was conducted by a dual culture method. The efficacy of B. siamensis RFCD306 on the inhibition of fungal growth and conidial germination was observed under the scanning electron microscope (SEM) and revealed the abnormal germination of conidial and hyphal growth. Moreover, four antibiotic synthesis-related genes consisting of srfA, ituA, bacD and bymA were detected from B. siamensis RFCD306 by a polymerase chain reaction (PCR) technique. These genes might be involved in the antifungal activity of the antagonistic bacterium. Furthermore, the disease control efficiency of B. siamensis RFCD306 was evaluated on harvested longan fruits and showed that the bacterium decreased the incidence of fruit rot disease. Therefore, this study represented the effective B. siamensis RFCD306 for using as a biological agent in controlling postharvest fruit rot disease of longan.