Abstract

The genus Colletotrichum consists of many economically important pathogenic fungi on a broad range of host plants world-wide. They cause significant economic losses to tropical crops: fruits, cereals, grasses, vegetables, etc., due to diseases at different stages of plant development. Several species of Colletotrichum cause anthracnose on coffee and other major crops, which are valuable trade commodities in Vietnam and Thailand. However, populations of these pathogens have been poorly studied so far. This thesis aims to identify species of Colletotrichum that are associated with anthracnose diseases on tropical crops, particularly coffee in Vietnam, and to characterise the populations of these pathogens. Studies on morphological, cultural and biochemical characteristics, pathogenicity, genetic diversity and population structures of the pathogens were employed. Random amplified polymorphic DNA (RAPD), unanchored/anchored microsatellite primed PCR (MP/AMP-PCR) and DNA sequence analysis of the mating type genes, the internal transcribed spacer region of nuclear ribosomal DNA (rDNA) and a portion of mitochondrial small subunit rRNA gene were used for diversity studies and in assisting species identification to complement the morphological data. Colletotrichum gloeosporioides and C. acutatum were identified from diseased citrus, grape, asparagus, mango, durian, etc. originating from Vietnam and Thailand. In Vietnam, C. gloeosporioides, C. actutatum, C. capsici, C. boninense and several Colletotrichum isolates of unknown species were found to be associated with infected coffee leaves, berries, roots and twigs in different coffee growing areas. No evidence was found of the presence of C. kahawae in Vietnam. The majority of Vietnamese isolates belonged to C. gloeosporioides and they were more pathogenic on detached green berries than isolates of any of the other species. The isolates of C. gloeosporioides mainly grouped in accordance with geographical origin based on both RAPD and MP/AMP-PCR markers. High genetic variation in populations of C. gloeosporioides from different locations and different coffee tissues was observed. Moderate gene differentiation was found between the populations of northern and southern Vietnam. However, within the regions there was low and no differentiation between locations and host tissues, respectively, indicating significant gene flow. This thesis provides better insights into the Colletotrichum populations that may play an important role for future disease management strategies in sustainable coffee production in Vietnam.