Dormancy and photosensitivity as premaize traits

One of the early effects of domesticating teosinte into maize must have been a genetic removal of dormancy from the mature seed so that the seed would germinate uniformly soon after planting. If the removal is carried too far in certain mutations we get a lethal condition known as uninterrupted embryo development in which the ear is a mass of seedlings at harvest time. In wild populations of teosinte, once its fruit cases reach the ground, dormancy substances in the seed inhibit germination until environmental conditions have removed them, which is usually adjusted to last until the most favorable time for growth. Variable soil conditions in nature result in corresponding differences in germination.

Synchronous flowering is usually important to cross-pollinated plants such as teosinte and maize in order to maintain heterozygosity and optimum size of an interbreeding gene pool. If variation in the time of germination resulted in isolation by flowering time, it could have harmful effects associated with inbreeding depression. Therefore, the dormancy trait became associated with another trait that insured uniform flowering. This trait, involving floral induction by short day-lengths continuing over a 2 to 3 week period, is now characteristic of all wild races of teosinte and to a lesser degree of certain tropical races of maize. Once induced, teosinte flowers regardless of plant size while short-day maize has a minimum length for the vegetative phase. Tropical maize tends to have large late-flowering plants that only tend to respond to short-day lengths.

Walton C. Galinat

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

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