YIELD, HETEROSIS AND INBREEDING DEPRESSION OF SINGLE CROSSES OF MAIZE

Information was obtained from evaluating the F-1, F-2 and F-3 of 45 single crosses among ten maize inbred lines with nine or more generations of selfing. Such inbred lines were randomly derived from the maize composite Xolache of the Chalqueno race. General and specific combining effects (GCA and SCA) were estimated for lines and crosses, respectively and the genetic structure (X-ij = mu+g(i)+g(j)+s(ij)) of each cross was constructed. Based on the genetic structure, it was possible to explain the potential yield, heterosis and inbreeding depression of each cross. High yielding crosses were those having at least one high general combining ability inbred line and high positive SCA effects. Reversely, low yielding crosses had at least a low GCA inbred line and high negative SCA effects. High yielding crosses with high heterosis had at least one high GCA inbred line and high positive SCA effects. On the other hand, high yielding crosses with low heterosis were those having at least one high GCA inbred line and low negative SCA effects. High yielding crosses with high inbreeding depression had at least a high GCA inbred line and high positive SCA effects. Reversely, high yielding crosses with low inbreeding depression had both inbred lines with high GCA and low positive or negative SCA effects. The most important inference derived from the genetic interpretation of the components of the genetic structure of single crosses is that any hybrid maize program should it have a base of high GCA inbred lines, and that by single crossing should be possible to identify those crosses presenting the highest heterosis.