Changes in physiological traits associated with five cycles of S1 recurrent selection in two maize populations

Maize populations BS13(SCT) and BSSS2(SCT) were evaluated after five cycles of S(,1) recurrent selection for cold tolerance. The C0, C5, and C0 x C5 population cross of both populations, and the C0 x C0 and C5 x C5 interpopulation crosses were evaluated in five environments involving three years. Experiments were planted after 20 April in central Iowa. Correlated changes in physiological traits were assessed by comparing means of C0 and C5 cycles and by estimating genetic changes across cycles;The selection programs reduced the number of growing degree days from planting to silking (6.9 growing degree days/cycle) in the two populations. Reductions in the time from planting to ear initiation and from ear initiation to silking also were observed. Time from planting to black layer and from silking to black layer were not changed in either BS13(SCT) or BSSS2(SCT). Correlated reductions in grain moisture at harvest were observed for both populations;No changes in grain yield were associated with the cold tolerant improvement in the two populations. However, a correlated increase in 300-kernel weights and decrease in number of ovules/ear at silking was observed in BSSS2(SCT). In BS13(SCT), selection for cold tolerance did not cause a correlated change in 300-kernel weights or in number of ovules/ear silking. Vertical root pull resistance was increased 2.65 lbs/cycle in BS13(SCT) and decreased 2.85 lbs/cycle in BSSS2(SCT);Plant sizes, sampled at various times during vegetative growth, were not changed substantially by selection for cold tolerance. Correlated changes in rate of ovule formation, root lodging, stalk lodging, harvest index, rate of grain fill, percentage grain moisture at black layer, prolificacy, and rate of dry down were not significant