EVALUATION OF CHANGES IN ADAPTED X EXOTIC MAIZE POPULATIONS IMPROVED BY ADAPTIVE MASS SELECTION (GERMPLASM, ZEA MAYS, YIELD STABILITY)

Populations containing exotic germplasm undergoing adaptive mass selection (AMS) in Nebraska were evaluated in two seasons. Incorporation of exotic germplasm populations was done by crossing them with adapted Corn Belt varieties, except in one case in which both parental populations were exotic. Backcrosses to the adpted parental population or random mating of the population hybrids was done for several generations before beginning AMS which was based on early maturity, yield assessed visually on the ear, number of ears per plant and freedom from disease. Two Corn Belt varieties were advanced in the same way as the semi-exotic populations as checks. The populations were grown in isolation plots each year as cycles were advanced. This study was done to evaluate these populations by comparing two generations from each population as far apart as possible. A Stiff Stalk Synthetic population improved by S1 testing scheme was included in the study as a check. Randomized Complete Block Design with split-plot arrangement was used, with populations as whole plots and generations as sub-plots. The experiments were repeated under five moisture regimes. The results suggest that AMS was effective in changing yield and maturity of the semi-exotic populations in the desired direction. Yield increases were associated with increased number of ears per plant, earlier maturity for the late maturing plants, decrease in silk delay and better stability under low yielding environments. The method failed to increase the proportion of upright plants resulting in significant decrease in some populations. Plant and ear heights decreased in most populations. Response to a yield index was inconsistent due to genotype x environment interactions. It is suggested that some of the populations need to be further improved for other important traits by mass selection or other selection schemes