Heat Stress Effects on Isolated Reproductive Organs of Maize

Abstract

The relative heat stress sensitivity of isolated reproductive organs was examined using two maize genotypes with known differences in thermal tolerance. In vitro pollination-fertilization procedures were used to expose various components of the reproductive process to elevated temperature. Fertilization percentage, as estimated by ovary swelling, and the percentage of kernel formation was measured. Heat stress during the stages of pollen shed, silk receptivity, pollen-stigma interaction, and/or early kernel formation adversely affected reproductive development. Fertilization per se appeared to be less sensitive to thermal stress than was kernel formation. The most sensitive stages appeared to be during pollen-stigma interaction and early kernel development. Differences between the two genotypes used in this study were expressed at the pollen and silk level. Exposure of LH74 tassels and/or silks to heat stress resulted in a significant reduction in kernel formation when compared to the nonstressed controls. Kernel formation frequency was not significantly reduced when Mo17 tassels or silks were exposed to heat stress prior to pollination. However, both genotypes were sensitive to elevated temperature during the pollen-stigma interaction and early kernel formation stages. The results from this study suggest that the development of heat stress tolerant germplasm would require reduced sensitivity not only during pollen shed and silk receptivity stages but also during pollen function and early kernel formation.