Morphology and molecular characterization of Colltetotrichum siamense associated with leaf spot disease of rubber tree (Hevea brasiliensis) in southern Thailand

Abstract

Rubber (Hevea brasiliensis) is an economically important crop in Thailand, especially in the southern part of Thailand where the climate is suitable for cultivation. In our recent survey of rubber plantations, rubber trees infected with several fungal pathogens resulting in leaf spot, leaf blight, and in severe cases, leaf defoliation, were observed in the field. These symptoms have not been observed previously and can be considered a novel leaf fall disease. To date, the pathogens causing leaf diseases on rubber trees in Thailand have been characterized to be caused by fungi in the genera Calonectria, Lasiodiplodia, and Neopestalotiopsis. However, species in the genus Colletotrichum, as fungal pathogens that cause leaf spots on rubber trees in Thailand, have not been characterized. Therefore, the aim of this study was to identify and characterize Colletotrichum siamense associated with rubber leaf spot disease with morpho-molecular studies combined with pathogenicity tests. Morphological characteristics revealed that isolates PSU-108, PSU-109, PSU-110, and PSU-111 belong to Colletotrichum sp., whereas multigene phylogenetic analyses with actin (act), calmodulin (cal), chitin synthase-1 (chs-1), glyceraldehyde-3-phosphate dehydrogenase (gapdh), and internal transcribed spacer (ITS), identified these isolates as Colletotrichum siamense. Hence, this report suggests C. siamense as the causal agent of leaf spot disease on rubber tree leaves. The findings in this study could be helpful for the development of appropriate measures to manage plant disease in rubber tree fields.