Temporal Sensitivities of Rice Seed Development from Spikelet Fertility to Viable Mature Seed to Extreme-Temperature

Extreme temperature during reproductive development affects rice (Oryza sativa L.) yield and seed quality. A controlled-environment reciprocal-transfer experiment was designed where plants from two japonica cultivars were grown at 28 and 24 degrees C (day and night temperatures) and moved to 18 and 14 degrees C and vice versa or from 28 and 24 degrees to 38 and 34 degrees C and vice versa, for 7-d periods to determine the respective temporal pattern of sensitivity of spikelet fertility, yield, and seed viability to each temperature extreme. Spikelet fertility and seed yield per panicle were severely reduced by extreme temperature in the 14-d period before anthesis; both cultivars were affected at 38 and 34 degrees C while only Gleva was affected at 18 and 14 degrees C. The damage was greater the earlier the panicles were stressed within this period. Later-exserted panicles compensated only partly for yield loss. Seed viability was significantly reduced by 7-d exposure to 38 and 34 degrees C or 18 and 14 degrees C at 1 to 7 d and 1 to 14 d after anthesis, respectively, in Gleva. Taipei 309 was not affected by 7-d exposure at 18 and 14 degrees C; no consistent temporal pattern of sensitivity was evident at 38 and 34 degrees C. Hence, brief exposure to low or high temperature was most damaging to spikelet fertility and yield 14 to 7 d before anthesis, coinciding with microsporogenesis; it was almost as damaging around anthesis. Seed viability was most vulnerable to low or high temperature in the 7 or 14 d after anthesis, when histodifferentiation occurs.