A correlation between knob number and leaf number-a counting mechanism

Most of the very early races or lines of maize have only 9 or 10 leaves at maturity. Since their mature seeds already have 5 or 6 preformed leaves, the remaining 3 or 4 must have cell initial areas that are already present in the apical dome. Since ears are initiated at the base of leaves 3 or 4 in mature seed, the anlagen of ear buds should be in place. Also the cells at the top of the dome, which form the tassel, should have more preformed cells than lines that grow a lot more.

One of the earliest selections that we know about is Early Early Synthetic (EES) from D. E. Alexander. EES is knobless except for a very small knob at 9S. Its background is mostly Gaspe. It is well known that Northern races and knobless flints are the earliest to come to maturity. If one plots the number of homozygous knob sites on one axis and the number of leaves on the other, a rather good correlation results. Knobless or low knob lines (1-2) have the fewest leaves. Intermediates with 3 to 5 knobs have more leaves and of course Southern and Mexican races (6 to 16) have the most leaves. Our morphological and cytological observations would suggest that knobs have a function to delay flower formation by controlling the initiation of more leaves. Since this significance on flower regulation was only realized during the summer of 1986, considerably more information must be obtained. However enough is known now about the maize of North America (Chiapas to Canada) to be convinced of the proposed correlation. Finally, it appears that the placement of the topmost ears may be the best predictor of maturity. The pre-set placement of the ear on the shoot is under genetic control and regulated by knob composition. At tasseling the ear also takes over apical dominance. This switch of dominance is of theoretical and practical interest.

Dale M. Steffensen and Sajjad R. Chughtai

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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