Molecular taxonomic, epidemiological and population genetic approaches to understanding yam anthracnose disease

Abstract

Water yam (Dioscorea alata L.) is the most widely cultivated yam species globally. The major limitation 
to the profitable and sustainable production of D. alata is its susceptibility to anthracnose disease. The 
availability of resistant varieties could potentially form the cornerstone of an integrated management 
strategy for yam anthracnose; however, anthracnose resistance breeding is hampered by the dearth of 
knowledge on pathogen identity and diversity. Four forms of Colletotrichum are now known to be 
associated with foliar anthracnose of yam: the slow-growing grey (SGG), the fast-growing salmon 
(FGS), the fast -growing olive (FGO), and the fast-growing grey (FGG) forms. The close phylogenetic 
relationship of the first three forms to reference isolates of Colletotrichum gloeosporioides, and the fact 
that only strains of these forms have been observed to induce typical anthracnose symptoms on D. 
alata , recently confirmed that C. gloeosporioides is the causal agent of yam anthracnose disease. The 
FGG form possibly represents a distinct, endophytic, species as indicated by morphological, biological 
and molecular criteria. Previous research emphasized epidemiology and control but limited progress 
was made in understanding yam anthracnose disease based on this classical approach. Molecular 
approaches have started to unravel the systematics and ecology of Colletotrichum strains associated 
with yam anthracnose, as well the population biology of C. gloeosporioides on yam. Sexual 
recombination is a likely mechanism contributing to the high genetic diversity of C. gloeosporioides in 
yam-based cropping systems. Studies have been initiated to understand the mechanisms that generate 
genetic variation in C. gloeosporioides, and to gain some insight into the biochemistry of the 
interactions between the pathogen and yam. Our thesis in this article is that integrating traditional and molecular approaches to understanding C. gloeosporioides systematics, epidemiology and population 
genetics will lead to a much better understanding of yam anthracnose disease, and thus to the 
development of effective and sustainable control measures. Research successes and challenges are 
discussed, as well as their implications for future studies on pathogen evolutionary potential, 
anthracnose resistance breeding, and the deployment of resistance genes.