Resistance in water yam (Dioscorea alata) cultivars in the French West Indies to anthracnose disease based on tissue culture-derived whole-plant assay

Reactions of 60 water yam (Dioscorea alata) cultivars to three isolates of the yam anthracnose fungal pathogen (Colletotrichum gloeosporioides) were evaluated using tissue culture-derived whole-plant assay. Three disease parameters: single score on a scale of 0-6 at the seventh day after inoculation (SD7); area under the disease progress curve (AUDPC); and disease progress rate (R-d) were compared, and cultivars were classified into disease-response groups using a rank-sum method based on AUDPC scores for the two most virulent isolates. A wide range of variation in resistance of the D. alata cultivars, and significant effects of pathogen isolate and isolate-cultivar interactions, were observed for all disease parameters. The three disease parameters were positively correlated; however, four cultivars showed great dispersions from the regression lines for comparisons of SD7 with the multiple assessments based AUDPC and R-d. The 60 cultivars were separated into resistant (n = 12), moderately resistant (n = 19), moderately susceptible (n = 18) and susceptible (n = 11) groups. The potential of the tissue culture-derived whole-plant assay to resistance breeding programmes and further understanding of the yam anthracnose pathosystem is discussed.