Combining ability and gene action in a diallel cross of eight sesame genotypes

An 8 x 8 diallel cross mating design with the parents and F1s excluding the reciprocals was used to estimate gene action and combining ability analysis for yield and some yield components in sesame (Sesamum indicum). These genotypes were evaluated at the National Semi- Arid Resources Research Institute (NaSARRI), Serere, Uganda. The investigation was carried out during the second season of 2013. Most of the sesame genotypes available in Uganda have low seed yields. A number of yield related components contribute to yield. The genes underlying these genotypes have not been documented. The present study was conducted to estimate the combining ability for twelve traits viz. days to maturity, plant height, 1000 seed weight, height of first capsule on the main stem and yield per plant among others. The genetic variance of combining ability was separated into general (GCA) and specific (SCA) combining ability variance components. Baker’s ratio, coefficients of genetic determination (CGD) were determined for narrow and broad sense. Effects due to GCA and SCA were analysed. High GCA effects were recorded for days to flowering (31.925***), plant height (105.7*), number of branches per plant (1.709*), number of capsules on main stem (22.417*), number of capsules on branches (178.01**), length of the capsule fruitinf zone (191.17***), capsule length (0.117***) and capsule width (0.0028*). This is due to additive gene action. SCA showed significant effect for only the number of capsules on branches (99.96*) and yield per plant (2.97*). Baker’s ratio was high for most of the traits except for yield per plant (0.233). CGDbs was also high for most of the traits except for days to maturity (0.064), plant height (0.346), capsules on main stem (0.358) and capsule width (0.286).