RELATIONSHIP BETWEEN MAJOR GENE CONTROLLED INFLORESCENCE MORPHOLOGY AND CONTINUOUS VARIATION FOR FINAL HEIGHT IN NICOTIANA-RUSTICA

Inflorescence morphology is a major discontinuity among Xicotiana rustica varieties and is controlled by major genes at, at least, two loci, which display duplicate non-allelic interactions. Its contribution to continuous variation for final height has been examined in F1, F2 and backcross families of a diallel set of crosses among eight inbred lines and in the F9 families of one of the crosses. It makes no direct contribution, but if all plants are divided into mop and nonmop types of inflorescence most of the variation in final height within each type can be accounted for by the variation in flowering time. Inflorescence morphology appears to switch the correlation between flowering time and final height from a very high negative value within the mops to a very high positive value within non-mops. Most of the non-allelic interactions for final height occur in crosses between a mop and a non-mop parent. These results imply that the major genes controlling inflorescence morphology exercise a critical control over the continuous variation for final height. However, to explain the lower correlations in the F9 families and the positive correlations among mop head varieties not included in the diallel it is necessary to assume that allelic differences at loci that are not concerned with inflorescence morphology are also involved in the switch. © 1979 The Genetical Society of Great Britain.