THE GENETIC-BASIS OF HYBRID VIGOR IN A HIGHLY HETEROTIC CROSS OF NICOTIANA-TABACUM

The genetical control of F-1 heterosis, observed in a cross of desirab le Nicotiana tabacum varieties, was investigated by analysing the data of the basic generations, triple test cross-families and random sampl es of doubled haploids (DH) and single-seed descent (SSD) lines. Analy ses of the first-degree statistics revealed a complex control underlyi ng the genetic variation, including the presence of epistasis, linkage , maternal effects and their interactions, in addition to the additive and dominance effects of the genes segregating in the cross. These an alyses identified gene dispersion, directional dominance, and duplicat e epistasis, as the main causes of heterosis. The triple test-cross an alysis also confirmed the presence of non-allelic interactions and ind icated that the dominance ratio, although inflated by epistasis, is co nsistently partial for all the traits. The extent of transgression in the recombinant inbred lines finally established unequivocally that, a s in numerous other crosses, gene dispersion and unidirectional, but p artial, dominance are the true causes of heterosis in this cross too.