Changes in germination ability and longevity were monitored during seed development in three japonica rice cultivars and one indica rice cultivar sown on three different dates, 14 October 1993, 24 November 1993 and 5 January 1994 at Los Baños, Philippines. Germinability of the seeds varied among cultivars in the early stages of development, but it was generally similar across sowing dates. The estimates of potential longevity (determined by storage at 40°C and 15% moisture and quantified by the values of the seed lot constant K1 of the viability equation) differed among cultivars and sowing dates. While the maximum potential longevity attained across different sowing dates was similar in the japonica cultivars Ju ku and Chianan 8, it was significantly higher in the first sowing than in the second or third sowings in cv. Akihikari. In the indica cultivar IR 58, maximum potential longevity attained in the second and third sowings was significantly greater than that in the first sowing. The mean potential longevity, averaged over cultivars and sowing dates, was marginally higher in the first sowing (K1=3.81) than in the second (3.65) and third (3.63); and averaged over cultivars and harvest times it was greatest at 34.8 days after flowering (DAF) in the first sowing, 31.8 DAF in the second and 28.3 DAF in the third. These results suggest that sowing in mid-October to allow seed ripening to coincide with the cooler and drier segment of the Los Baños dry season, and harvesting 35 DAF can improve the potential longevity of some japonica cultivars.
Kameswara Rao, N.; Jackson, M.T. Effect of sowing date and harvest time on longevity of rice seeds. Seed Science Research (1997) 7 (01) 13-20. [DOI: 10.1017/S0960258500003317]