Responses to Mass Selection in Maize and Stability of Resulting Populations1

Abstract

Four mass‐selected populations of maize (Zea mays L.), the base population ‘Hays Golden’ (H.G.), and a double cross hybrid check ‘Nebr. 501D’ were evaluated in a range of environments involving five locations and 3 years. The four mass‐selected populations were: C15, the 15th generation of selection for high grain yield; I15, the 15th generation of selection for high grain yield following treatment with thermal neutrons in early cycles of selection; P10, the 10th generation of selection for increased prolificacy; and I14E3, the third generation of selection for yield plus earliness, low ear height, and stalk quality after 14 generations of selection for only high grain yield following irradiation with thermal neutrons.Mass selection significantly increased grain yield 12 to 15% on the average. When selection was for high grain yield only, correlated increases occurred in prolificacy, days to flower, plant and ear height, and gram mmsture at harvest. Selection for earliness and low ear height in a population previously selected for high grain yield seemed effective without reducing yield. Ten cycles of selection for prolificacy were about as effective in in. creasing yield as 15 generations of selection for yield itself. At the same time, grain moisture did not change and days to flower, plant height and ear height increased less than in selection for yield.Responses to environment mean yields were all linear and were much greater in mass‐selected populations than in H.G. or in the Nebr. 501D hybrid. Selection appears to have increased the frequencies of those genes which permit genotypes to take advantage of more favorable growing conditions. Under low yield levels caused by heat and drouth, the original population performed as well as or better than mass‐selected populations. However, when grown under favorable conditions, mass‐selected populations had substantially greater yields. Differences in yield responses under varying environments may be related to correlated responses that have occurred in mass selection programs.