Sex determination in monoecious plants like maize has been shown to be influenced by genotype, daylength, and plant hormones. In a recent series of experiments to determine the physiological effects of an anti-dehiscence chemical, 3-(p-chlorophenyl)-6-methoxy-s-triazine-2,4(1H, 3H) dione triethanolamine, DPX-3778 (E.I. du Pont de Nemours), the sex determination of the tassels was found to be altered depending on the concentration and timing of DPX-3778 application. Chemical treatments have been conducted on two hybrids (Seneca 60 and Golden Beauty) and an inbred (Oh43). Multiple applications of 0.005% DPX-3778 to the leaf sheath of maize plants or the addition of 1 ppm of DPX-3778 to hydroponic growth medium approximately 4 weeks before anthesis caused almost complete reversion of staminate inflorescences to pistillate inflorescences (Fig. 1 and 2). In addition to the normally developed gynoecium of the upper floret, DPX-3778 treatment resulted in the full development of the gynoecium of the lower floret of the ear spikelets. Both the spikelets in the tassel and ear inflorescences could produce viable seeds if pollination occurred (Fig. 3). The net result of DPX-3778 treatment is "male sterile" inflorescences. These results could be duplicated in northern teosinte (Zea mays subsp. mexicana, race Nobogame) (Fig. 4). Our results indicate that DPX-3778 could be useful for elucidation of sex determination in grasses.
P.C. Cheng and D.C. Wright
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