Six cycles of selection for adaptation in two exotic populations of maize
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The maturity rating of maize (Zea mays L.) grown in Galicia (Northwestern Spain) varies from FAO 200 to 600. Later germplasm has usually too much moisture content in the kernel at normal harvesting time so serious problems with storing could appear. Besides, farmers have tended to use earlier varieties in the last few years. All this imposes limitations on the amount of germplasm available to develop varieties adapted to this area. To study the possibility of adapting late, exotic material to the environment of the Atlantic coast of Galicia we carried out six cycles of individual selection on two non-adapted populations of maize (Purdue A and Purdue B). The criterion of selection was early silking and the criterion of response was moisture content of kernel at harvesting. The original populations and the populations obtained after each cycle of selection were crossed to the hybrids CM105 CM109 (tester Reid) and H99 H95 (tester Lancaster) and were evaluated in four 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 O to cycle 6 for Purdue A and Purdue B, respectively) and grain moisture at harvesting (3.0 and 3.9% from cycle O to cycle 6 for Purdue A and Purdue B, respectively). There were also reductions in plant height and yield in both populations. In general, the crosses 'population Lancaster' were higher for yield than the crosses 'population 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. 1996 Kluwer Academic Publishers.
