Inheritance of resistance in water yam (Dioscorea alata) to anthracnose (Colletotrichum gloeosporioides)

Colletotrichum gloeosporioides causes anthracnose, the most severe foliar disease of field-grown water yam (Dioscorea alata). The inheritance of resistance to a moderately virulent (FGS) strain of the pathogen was investigated in crosses between tetraploid D. alata genotypes: TDa 95/00328 (resistant)xTDa 95-310 (susceptible) (cross A), and TDa 85/00257 (resistant)xTDa 92-2 (susceptible) (cross B). Segregation of F-1 progeny fitted genetic ratios of 3:1. 5:1 (crosses A and B) and 7:1 (,cross A) resistant: susceptible when inoculated with the FGS strain. indicating that resistance is dominantly inherited and suggesting that more than one gene controls the inheritance of resistance to this strain in the accessions studied. When parental and progeny lines of cross A were inoculated with an aggressive (SGG) strain of the pathogen, all plants expressed a susceptible phenotype, indicating strain-specific resistance in TDa 95/00328. Screening of 20 cultivars/landraces confirmed the high susceptibility of D. alata accessions to the SGG strain and revealed the presence of apparent strain non-specific resistance in TDa 85/00257. TDa 85/00257 and TDa 87/01091 which were resistant to the SGG strain, will be useful both as sources of resistance and in the development of a host differential series for D. alata.