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Morphological and molecular characterization of Colletotrichum species causing anthracnose in soursop (Annona muricata)

Nimal Adikaram: National Institute of Fundamental Studies

<div>Soursop (<em>Annona muricata</em>), belonging to the family Annonaceae, is a popular source of fruit juice and has numerous medicinal properties. Anthracnose is a major postharvest disease of ripe soursop responsible for substantial postharvest losses. The disease was earlier believed to be caused by <em>Colletotrichum gloeosporioides </em>and <em>Colletotrichum acutatum</em> which are presently considered as species complexes. The objective of the study was to identify <em>Colletotrichum </em>species associated with anthracnose in ripe soursop fruit using morphological characters and multi-gene sequence analysis. <em>Colletotrichum </em>was isolated from anthracnose lesions on ripe soursop, collected from the Central and North Western Province of Sri Lanka. Morphometric analysis, using eleven characters ranging from colony, conidial to appressorial morphology, divided the twenty isolates into two main clusters, conidial size being the most contributing factor for cluster separation. Ten isolates representing the two clusters were subjected to DNA sequence analysis, using ITS, β-tubulin 2 (TUB2) and GAPDH as gene regions. For resulting sequences, the species affiliations and identities were determined through similarity-based searches of the NCBI GenBank Database. Considering 95% similarity, <em>Colletotrichum siamense </em>and <em>Colletotrichum fructicola </em>were identified as pathogens associated with soursop anthracnose. Both species are belonging to the <em>C. gloeosporioides </em>complex. ITS region contributed in placing the taxa within <em>C. gloeosporioides </em>while TUB2 and GAPDH determined their identity to species level. This is the first report of <em>C. fructicola </em>and <em>C. siamense </em>from soursop anthracnose.</div>