Whitefly resistance in African cassava genotypes
Whitefly (Bemisia tabaci), a major pest and vector of viruses in cassava, is the greatest current threat to cassava production in sub-Saharan Africa (SSA). Research efforts have focused on management of the two viral diseases: cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), and have ignored the whitefly vector that is driving the spread of the viruses, causing CMD and CBSD in SSA. The objective of this study was to evaluate cassava genotypes for resistance to B. tabaci based on field infestation and damage in Uganda. The study was carried out in four sites with diverse agro-ecologies including: Namulonge, Kasese, Ngetta and Serere during 2015 and 2016.Whitefly nymph abundance and feeding damage were assessed on each test genotype from 3 to 6 months after planting (MAP). In 2015, the highest broad sense heritability estimates were 39% (4 MAP) and 53% (5 MAP) for whitefly nymph abundance and feeding damage, respectively. In 2016, broad sense heritability estimates were 23% (3 MAP) and 41% (4 MAP) for whitefly nymph abundance and feeding damage, respectively.Analysis of variance of whitefly nymph abundance showed a significant (P< 0.05) location × genotype × season interactions at 3, 4, 5 and 6 MAP. There were also significant (P< 0.05) location × genotype × season interactions at 3 and 4 MAP for whitefly feeding damage. Ten genotypes showed good levels of resistance to whitefly infestation and feeding damage including: UG120202, UG120174, NASE13, UG120160, UG120286, UG120293, UG130075, CSI-142, CS1-144 and UG130085. These genotypes may serve as parental materials for breeding programmes for whitefly and viral disease control.
Key words: Bemisia tabaci, cassava brown streak disease, cassava mosaic disease