Monday, August 19, 2019 at 11:00am to 12:00pm
Cassava (Manihot esculenta Crantz), an essential source of food for about 800 million people worldwide, ranks as the second most important staple food crop in Uganda. Despite the role cassava plays in the livelihood of farmers, the adoption of improved varieties remains low, in part because some improved varieties do not have the root quality traits preferred by end-users. To contribute towards breeding for varieties suitable for end-user needs and preferences, I conducted three studies: 1) A study of cassava traits preferred by smallholder farmers in four districts within Uganda. Results revealed that the predominant attributes preferred by smallholder farmers were yield (many roots and big root size), early maturity, and root quality (taste, long in-ground storability of roots, softness of cooked roots, and non-bitter roots); 2) A study on the heritability of softness of cooked cassava roots, one of the key traits preferred by end-users. Softness was defined as the maximum force (N) needed to penetrate cooked root samples using a penetrometer. It was evaluated at four cooking time intervals: 15, 30, 45, and 60 minutes on 268 cassava genotypes. Estimates of broad-sense heritability (repeatability) ranged from 0.17 to 0.37, with the highest value observed at 45 min of cooking time. I also quantified the relationship between penetrometer and consumer testing methods for phenotyping softness of cooked cassava roots. Results from the two methods were strongly correlated (r2 = 0.91; P-value = 0.003), suggesting a penetrometer can be used for phenotyping cooked root softness; 3) A study to determine the genetic relationships of cassava varieties grown by smallholder farmers in Uganda, and the relationship between farmer-grown varieties and breeding lines. I used genotyping-by-sequencing to score 287,952 single nucleotide polymorphisms in 547 samples of farmer-named cassava varieties collected by random sampling of 192 smallholder farms within four districts in Uganda, and a panel of 349 breeding lines from the cassava national breeding program in Uganda. Results indicated little genetic differentiation (FST < 0.05) between the varieties collected in different districts. Similarly, little genetic differentiation (FST = 0.020) was found between varieties grown by farmers and the breeding lines. Additionally, a low level of diversity was found among farmer-grown varieties and breeding lines. Thus, cassava breeding programs in Uganda could benefit from obtaining new sources of variation from other breeding programs. Given the low genetic differentiation between farmer-grown varieties and breeding lines, the improved varieties may not be significantly different from the locally adopted varieties, hence increasing the likelihood for adoption. The information presented in this study contributes to the understanding the genetic relationships of the available cassava germplasm and can be useful in cassava breeding and improvement efforts in Uganda.