Foliar Pathogenic Colletotrichum species Associated with Cultivated Rubber Trees in Sri Lanka

Abstract

Colletotrichum leaf disease (CLD) is regarded as one of the major threats on rubber trees worldwide. Due to recent revolutionary changes in species numbers in the genus Colleotrichum based on molecular data, it is essential to re-assess the Colletotrichum species associated with rubber trees in Sri Lanka. The objective of this study is to identify Colletotrichum species associated with rubber plants in Sri Lanka using morphology and DNA barcoding. Samples with leaf spots were collected randomly from rubber trees at selected sites in Colombo and Matale. Single spore isolation technique was followed to obtain five pure cultures of Colletotrichum spp. and their morphological characteristics were observed. Internal transcribed spacer (ITS) loci of all isolates were sequenced. Sequences were initially identified based on similarity search at NCBI and phylogenetic analysis was performed to further confirm the relative phylogenetic placement of Colletotrichum species. Pathogenicity tests were carried out to confirm the pathogenicity of the species and the Koch’s postulates were proven for potential pathogens. According to the morphological and molecular data, those isolates belong to C. gloeosporioides, C. gigasporium and C. truncatum species complexes. Two different species grouped within C. gloeosporioides complex showed highest growth rates in Potato Dextrose Agar (PDA) and Malt Extract Agar (MEA) whereas C. gigasporium and C. truncatum showed the highest growth rate in PDA and MEA respectively. Typical CLD symptoms were observed with C. gloeosporioides complex species after pathogenicity testing whereas C. gigasporium and C. truncatum were also able to colonize and produce spore masses on rubber leaves. According to our knowledge this is the first record of C. gigasporium and C. truncatum associated with rubber plants in Sri Lanka. Therefore, this study reveals the unknown diversity of Colletotrichum pathogens associated with cultivated rubber trees.