EFFECTS OF LOW RADIATION AND LOW-TEMPERATURE AT MEIOSIS ON POLLEN VIABILITY AND GRAIN SET IN WHEAT

Wheat plants at meiosis were subjected in a growth chamber to treatments combining 2 levels of temperatures (15/18 degrees C and 1.5/8 degrees C night/day) and 2 levels of radiation (203 +/- 26 and 11 +/- 1 mu mol m(-2) s(-1) photosynthetic photon flux density). Pollen viability at anthesis (fluorochromatic reaction) decreased in response to low radiation, but was not affected by chilling. There was no interaction between radiation and temperature. Varieties Moulin and Pernel had qualitatively the same response, but Moulin was more sensitive. These results were validated in 2 field experiments on Pernel. In the first, plants were exposed to -2 degrees C for 1 h on 3 consecutive days at different stages around meiosis. Cooling slightly reduced grain set, but there was no difference in the sensitivity of the developmental stages. In the second field experiment, plants were shaded at meiosis to receive 30% of the solar radiation. Shading strongly reduced kernel number per ear and induced sterility.