Durian (Durio zibethinus L.) is an economically important crop in the southern and eastern parts of Thailand. The occurrence of die-back disease caused by plant pathogenic fungi poses a serious threat to the quality and quantity of durian products. However, the identification of causal agents has been a subject of mixed information and uncertainty. In this research, we conducted a comprehensive investigation of die-back disease in nine durian plantations located in Thailand. By analyzing a total of 86 Fusarium isolates obtained from infected tissues, we aimed to provide clarity and a better understanding of the fungal pathogens responsible for this economically significant disease. Through a combination of colony characteristics, microscopic morphology, and a multilocus sequence analysis (MLSA) of the internal transcribed spacer (ITS) region, translation elongation factor 1-α (TEF1-α) gene, and RNA polymerase II gene (RPB2) sequences, we were able to identify and categorize the isolates into three distinct groups, namely, Fusarium incarnatum, F. solani, and F. mangiferae. Koch's postulates demonstrated that only F. incarnatum and F. solani were capable of causing die-back symptoms. This research represents the first report of F. incarnatum as a causal agent of die-back disease in durian in Thailand. Additionally, this study uncovers the association of ambrosia beetles and F. solani, highlighting the potential involvement of E. similia in facilitating the spread of die-back disease caused by Fusarium in durian.
Keywords: Fusarium; ambrosia beetle; durian; pathogenicity; transmission.