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Environmental and Stress Physiology

Plant Factors Controlling Seed Set in Maize ¹

The Influence of Silk, Pollen, and Ear-Leaf Water Status and Tassel Heat Treatment at Pollination

Department of Agronomy, The Ohio State University, Columbus, Ohio 43210, Department of Agronomy, University of Illinois, Urbana, Illinois 61801, North Central Soil Conservation Research Laboratory, United States Department of Agriculture, Agricultural Research Service, Morris, Minnesota 56267

In maize (Zea mays L.) large decreases in kernel number result when low water potentials (_w) and high temperatures occur during pollination. To gain insight into the basis for the decreased seed set, silk, pollen, and ear-leaf _w, the capability for silk osmotic adjustment, and pollen appearance were measured to determine their relationship to seed set. A multiple-eared or prolific (high carbohydrate availability to the pistillate inflorescence) hybrid (B73 x FR25), a heat sensitive hybrid (WF9 x A632), and a commercial hybrid (B73 x Mo17) were studied. A cross-pollination experiment, with pollination limited by pollen amount, was conducted to determine the impact on seed set of water and heat stressing the tassel and water stressing the ear. At low _w, silk _w and seed set were decreased whereas pollen _w, appearance, and viability were unaffected. High temperature resulted in a 2 megapascal decrease in pollen _w, visually damaged pollen being shed, decreased pollen viability, and, in two of the hybrids, substantially decreased pollen shed. Prolificacy did not result in increased silk solute accumulation but did result in superior seed production by the pistillate inflorescence at low _w. The magnitude of the decrease in silk solute potential was small (0.2 megapascal) and similar for all genotypes. One hybrid maintained a relatively high silk turgor but this hybrid also decreased the most in seed production when the pistillate inflorescence was water deficient. These results indicated an adverse effect of high temperature on pollen development, a positive relationship between seed production and silk water status, and no advantage to high silk turgor after silk emergence in maintaining seed production. Additionally, there was no evidence of variation in silk solute regulation capability among hybrids which varied in prolificacy, a trait important in drought tolerance, but the seed production of the pistillate inflorescence of the prolific hybrid was least affected by water deficit.

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