Limits to genetic divergence for occurrence of heterosis- experimental evidence from crop plants

Abstract

Two experiments in groundnut (Arachis hypogaea L.) and one in rapeseed (Brassica campestris L.) involving varying number of crosses made to diallel and line x tester designs were studied with the aim of relating genetic divergence among parents with the frequency and magnitude of heterosis in the F₁ generation. A method was devised to delineate the divergence among parents into four divergence classes, DC1, DC2, DC3 and DC4. Heterosis was computed as per cent improvement over the value of better parent, for three important components of yield in each crop. Genetic divergence was measured by D² statistic. If m is the mean and s the standard deviation of divergence values (given by D²) among parents, it was postulated that two parents whose genetic divergence falls between (m-s) and (m+s), i.e., in the classes, DC2 and DC3, when crossed will have higher chances of producing high frequency and magnitude of heterosis when compared to a cross whose parental divergence falls outside the limits, (m-s, m+s).