Distribution of resistance of cassava genotypes to dry, soft and black root diseases and correlation to yield parameters

Abstract

AbstractRoot rot is one of the most limiting diseases of cassava production in the Northeast Region of Brazil, causing root‐yield loss from 30% to 100%. This study aimed to evaluate the resistance of 76 cassava genotypes to dry (Fusarium spp.), soft (Phytophthora melonis) and black (species of the Botryosphaeriaceae family) root rot diseases. The roots were inoculated separately with isolates belonging to each of three disease group (dry, black and soft), by using the whole tuberous root inoculation method. The lesioned areas on the tuberous roots were measured by digital image analysis. Based on cluster analysis, four groups were found associated with the resistance to root rot diseases. About 10% of the genotypes were classified as resistant to dry and soft root rot, and 2% were classified as resistant to black root rot. Moreover, only 2% of the genotypes showed multiple resistance to these disease groups. Significant correlations were found between root peel and pulp infections by the same fungus, and between the root peel infections caused by P. melonis and Fusarium spp. These findings will be essential in the generation of plants with resistance to multiple root rot pathogens and will guide the cassava breeding programme to obtain superior varieties.