No abstract

Most crops, including sweetpotato vary widely in yield performance across different agro-ecological environments. This study was set up to determine the genotype x environment interaction (GEI) for storage root yield performance of 24 sweetpotato genotypes in eight environments; two locations -Kiboko and Thika, two moisture stress conditions -drought stress and no drought stress, and two years -2011 and 2012 in Kenya. Plots of three rows each of 10 plants per genotype, at density of 0.9 m × 0.30 m were panted during dry season under split plot design replicated twice. Managed irrigation was applied to control moisture stress during the growth period. Fresh storage root yield (FSR) data was collected, and drought susceptibility indices (DSI) determined. Additive Main Effects and Multiplicative Interactions (AMMI) genotype main effect by genotype-environment (GGE) interaction biplots and regression analyses were done using Genstat 14 th edition to determine GEI effects. The environment, genotype main effects, and the GEI were all significant (P < 0.001). The DSI showed significant variation of genotypes in different environments. The highest yielding genotypes across the environments were G7, G14, G15, and G10 while most stable genotypes were G5, G22 and G2 and the least stable was G24. Thus, genotypes G5, G22 and G2 may be used across environments, while genotypes G7 and G14 could be used, 1) in specific locations to boost production under unpredictable rainfall conditions, 2) incorporated into drought screening breeding programmes to develop a new generation of drought tolerant sweetpotato varieties to meet changing climatic conditions.

Analysis of the gene action exhibited by an agronomic trait in crop plants is useful in the planning of an effective plant breeding program. This study sought to establish the inheritance variance of root yield components and beta carotene content present in sweet potato clones commonly grown in Kenya. Ten contrasting parents were selected based on their beta carotene content, dry matter content and yield potential. They were planted in pots in the green house at KEPHIS-Muguga, Kenya, where they were grafted into Ipomoea setosa to boost their ability to flower. Five parents were further selected based on their ability to flower under local environmental conditions and crossed in a 5 × 5 half diallel manner. Five parents and ten F 1 clones arising from this hybridization were evaluated at KALRO-Kiboko, Kenya during two rainy seasons. The field trials were laid out in a randomized complete block design of three replications. The data were scored for root yield characteristics, beta carotene and root dry matter content. Griffing Method II, Model 1 diallel was used to estimate the general and specific combining ability. Genetic variability for beta carotene and root dry matter content indicated that the two traits were controlled mostly by both additive and dominant gene actions. Heterosis gene effects were found for beta carotene and root dry matter content which would be useful in the improvement of sweet potato productivity.

Sweet potato is one of the most important staple crops in Sub-Sahara Africa because of its supply of carbohydrates, vitamin A and C, fiber, iron, potassium and protein.The objective of this study was to determine phenotypic variation in diverse sweetpotato varieties for marketable roots, fresh root yield, fresh biomass weight, harvest index, beta carotene content and root dry matter content. Twenty five sweet potato genotypes were evaluated at two sites in two seasons in Kenya using a randomized complete block design of three replications. The results indicated that there were highly significantly variations for genotypes and sites for all the traits studied. There were no significant differences for genotype x site x season effects for the traits except for the number of marketable roots and fresh root yield. The mean fresh root was 32.19 t/ha,with the genotype Ininda expressing the highest fresh root yield of 54.79 t/ha. Genotypes, Naspot 13, Ejumula, Kabode, Vitaa and Tio-Joe gave the highest beta carotene content ranging between 11.830 and 10.040 mg/100g; with a mean of 5.384 mg/100g. The mean root dry matter content was 24.84 % with clones Amelia and Melinda showing the highest and lowest root dry matter content of 30.62 and 16.52 % respectively. Ten genotypes including Ininda, Erica, Jane, Naspot 13, Ejumula, Kabode, Vitaa, Tio-Joe, Amelia and Mayai were recommended as potential parents for sweet potato breeding program in Kenya.