GAMETE SELECTION FOR HEAT-STRESS TOLERANCE IN MAIZE

The present study was designed to assess the feasibility of utilizing in vitro gamete selection as a means of developing heat-stress tolerant maize germplasm. A synthetic population known as «Arizona Arid Environment Maize» was used as a source of heat-stress tolerance, and two Corn Belt-adapted, heat-stress sensitive inbreds, B73 and LH74, were chosen for improvement. An in vitro pollination-fertilization procedure was utilized to generate a series of selected and non-selected progenies by exposing the gametes to elevated (38 °C) and normal (28 °C) temperatures, respectively. Two single crosses (B73 x AZIOO and LH74 x AZIOO) and two back-crosses [B73 x (B73 x AZIOO) and LH74 x (LH74 x AZIOO)] were made. Out of the of 9,914 ovaries pollinated in this study, 1,250 kernels were formed from which 689 plants were obtained. A total of 112 progenies (14 per cross x temperature treatment) were generated by self-pollinating the resulting in vitro-derived plants and evaluated for pollen germination at 38°C and agronomic performance under heat-stress conditions. In all four crosses, pollen from the selected progenies was less sensitive to heat-stress-induced reductions in germination than was pollen from nonselected progenies. Similarly, the agronomic performance of the selected progenies was superior as evidenced by higher grain yields, greater seedling vigor, and reduced stalk and root lodging. The results from this study demonstrate that exposure to elevated temperature during gamete function can influence the heat-stress tolerance of pollen in the following generation. They also support the contention that gamete selection can enrich the frequencies of genes associated with useful agronomic traits, such as heat-stress tolerance. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.