A general method for the detection of additive, dominance and epistatic components of variation III. F2 and backcross populations

Abstract

The advantages of the extended form of the design III experiment of Comstock and Robinson, which is a triple test cross, are illustrated by the analysis of design III and triple test cross experiments on the F2 and first back-cross generations of crosses between inbred varieties 1 and 5, and 2 and 12 of Nicotiana rustica grown in a number of environments. A modification of the analysis of Kearsey and Jinks is proposed and illustrated which retains the advantages of the original but makes fuller use of the families in the triple test cross that have the F1 as one parent. The results of the anlayses show the relative unimportance of dominance and epistasis compared with the additive component of variation for the characters plant height and flowering time in the cross 1 x 5 when grown in most environments. The non-additive components of variation, on the other hand, are an important element in the cross 2 x 12 in all environments. Because the estimates of the components of variation obtained from either of the experimental designs have similar or identical sampling errors and are uncorrelated the variation in their absolute and relative values over environments can be unambiguously attributed to genotype-environmental interactions. Comparisons over environments show that there are genotype- environmental interactions that are, in general, greater for the additive than for the non-additive action of the genes. The results of these analyses compare favourably with the cumulative information from larger experiments on the same varieties using a number of alternative designs. © 1970 The Genetical Society of Great Britain.