Genotype by Phytophthora colocasiae isolate interaction in breeding for resistance to taro [Colocasia esculenta var esculenta (L.) Schott] leaf blight disease in Ghana

Two experiments were undertaken to evaluate the resistance of 5 parents and 20 hybrids of dasheen taro (n = 25) developed through the diallel method to Phytophthora leaf blight disease which is also known as taro leaf blight disease (TLBD). The field experiment which was laid out in Randomized Complete Block Design with 3 replications assessed the disease incidence (%) and disease severity index (DSI%) among the genotypes planted in three (3) agro-ecological zones in Ghana. In the laboratory the parents and hybrids were inoculated with three (3) Phytophthora colocasiae isolates from Dormaa Ahenekro, Tano Dumasi and Bunso in the Bono, Ashanti and Eastern regions of Ghana respectively and the diameter of lesions formed on the leaves after five days of inoculation were measured. Significant differences (p < 0.05) among the parents and hybrids for resistance to the Phytophthora colocasiae isolates, TLBD incidence (%) and DSI (%) in the field were observed making room for selection for further breeding for resistant varieties of dasheen taro. The isolate effect and genotype by isolate interaction effect were not significant (p > 0.05) indicating the similarity of the isolates' virulence and pathogenicity and therefore any of the isolates identified can be used to screen for resistance to TLBD in Ghana. Hybrids BL/SM/115 × BL/SM/10, BL/SM/115 × CE/MAL/32, CE/MAL/32 × BL/SM/10, CE/MAL/32 × CE/IND/16 and CE/IND/16 × BL/SM/115 and parent CE/IND/16 were observed to have no disease incidence with corresponding zero DSI (%) making them highly resistant and therefore can further be field evaluated and be recommended to farmers for cultivation. The highly significant and positive predictive value for TLBD incidence and DSI (%) based on the lesion area on leaf discs suggests that resistant genotypes of TLBD can be selected at the laboratory without spending long periods of time and money for evaluating genotypes in the field.