An investigation of gene action and genotype × environment interaction in two crosses of Nicotiana rustica by triple test cross and inbred line analysis

Abstract

Data from two random samples of inbred lines and from the two sets of the triple test cross in which these inbreds are crossed to the pure-breeding parents and F1 of the cross from which they were derived, one involving material derived from the cross between varieties 1 and 5 of Nicotiana rustica and the other material from the cross between varieties 2 and 12, are analysed and the results compared to those reported earlier. Detection of epistasis and the estimation of the additive and dominance components of variation among the triple test cross families is based on the orthogonal analysis of Jinks and Perkins (1970) while the additive component is also estimated directly from the inbred families. Tests are carried out to detect genotype × micro-environment interaction in the L1 and L2 families of the triple test cross and in the inbred families and the interaction partitioned into that involving additive and dominance gene action. Their relationship with the corresponding additive and dominance components of mean performance is investigated by linear regression analysis. As expected the material from the V1 × V5 cross segregates at loci the alleles of which display large additive effects but little or no dominance and epistasis while dominance and epistasis are larger components of the genetic variation in V2 × V12 cross. In both crosses, the micro-environmental interaction involves mainly the additive genetic component. For some characters there is evidence of independent segregation of genes controlling environmental sensitivity. Estimates of the additive genetic component D from the triple test cross and the inbred families, are consistent for all the characters in both crosses. The triple test cross analysis, therefore, provides satisfactory estimates of the genetic variation among a random set of inbred lines, even for those characters which display non-allelic interactions.