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 treatmen ts combining 2 levels of temperatures (15/18 degrees C and 1.5/8 degre es 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 ra diation, but was not affected by chilling. There was no interaction be tween radiation and temperature. Varieties Moulin and Pernel had quali tatively the same response, but Moulin was more sensitive. These resul ts were validated in 2 field experiments on Pernel. In the first, plan ts were exposed to -2 degrees C for 1 h on 3 consecutive days at diffe rent stages around meiosis. Cooling slightly reduced grain set, but th ere was no difference in the sensitivity of the developmental stages. In the second field experiment, plants were shaded at meiosis to recei ve 30% of the solar radiation. Shading strongly reduced kernel number per ear and induced sterility.