We have examined the expression of lesion mimic genes and nuclear genes affecting plastid greening (ij, cm, j1, j2) in several inbred lines of maize. These observations are complicated by two factors: (1) differences in leaf shape and coloration in the inbred lines, and (2) inbred lines planted at the same time have a different number of leaves when measurements on leaf characters are made later in the season. This latter complication means that environmental influences are not comparable for the xth leaf's emergence in the various lines. This past summer we investigated why plants do not have the same number of leaves at specific times during the growth cycle. Ten-seed families of A188, A619, B37, K55, Ky2l, Mo17, Mo20W, N6J, Oh51A, Tr, W23 and Wg were planted for three weeks beginning May 17. The field was irrigated the next morning. Leaf number was recorded three times per week for the second planting and once per week for the first and third planting. Emergence was scored when at least 1" of leaf was visible at the top of whorl; measurements continued until tassel emergence. Surprising to us was the observation that all 11 inbred lines had an average leaf emergence rate of 0.375 leaf per day beginning with the 5-6th leaf and continuing for the rest of the season. Inbred lines differed substantially in the amount of time required to reach the 5th leaf stage. In the California environment at least it should be possible to stagger planting dates to synchronize plants of different genetic backgrounds to produce the 5th leaf, and hence all subsequent leaves, on approximately the same day.
Carolyn Thum and Virginia Walbot
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