6 CYCLES OF SELECTION FOR ADAPTATION IN 2 EXOTIC POPULATIONS OF MAIZE

The maturity rating of maize (Zea mays L.) grown in Galicia (Northwest ern Spain) varies from FAO 200 to 600. Later germplasm has usually too much moisture content in the kernel at normal harvesting time so seri ous problems with storing could appear. Besides, farmers have tended t o use earlier varieties in the last few years. All this imposes limita tions on the amount of germplasm available to develop varieties adapte d to this area. To study the possibility of adapting late, exotic mate rial to the environment of the Atlantic coast of Galicia we carried ou t six cycles of individual selection on two non-adapted populations of maize (Purdue A and Purdue B). The criterion of selection was early s ilking and the criterion of response was moisture content of kernel at harvesting. The original populations and the populations obtained aft er each cycle of selection were crossed to the hybrids CM105 x CM109 ( tester Reid) and H99 x H95 (tester Lancaster) and were evaluated in fo ur environments to study the efficiency of the selection scheme. There were significant reductions in days to silking (6.1 and 6.7 days from cycle 0 to cycle 6 for Purdue A and Purdue B, respectively) and grain moisture at harvesting (3.0 and 3.9% from cycle 0 to cycle 6 for Purd ue A and Purdue B, respectively). There were also reductions in plant height and yield in both populations. In general, the crosses 'populat ion x Lancaster' were higher for yield than the crosses 'population x Reid'. Yield of the population crosses by both testers decreased after the six cycles of selection probably because of the earlier maturity of the selected populations. Some inbreeding depression may also have occurred.