The effects of mixed direct seeding of parental lines with different hull colors on the seed production of hybrid rice

Abstract

Conventional production of hybrid rice seeds is based on sowing and transplanting parental lines separately (‘separate seeding and transplanting’, SST). To decrease the labour inputs of field management, a labour-saving model was implemented under a strategy of directly seeding the two parents as a mixture (‘mixed direct seeding’, MDS) to produce hybrid seeds. The strategy utilized a ‘yellow-hull/red-hull’ pair, ensuring that the female parent could be easily separated from the male parent after mixed harvesting. To assess the effects of MDS on seed production, two pairs, P88S/G-4 and Y58S/G-15, were tested and compared with those under SST at the same female/male seed ratio of 5:1 in 2015 and 2016. The parental lines for two pairs flowered synchronously, and the male sterile lines presented a high total stigma exertion rate in SST that ranged from 75.82% to 93.27%. At maturity, the hybrid seeds generated on seed parents were harvested together with those from pollen parents, and later, the hybrids were successfully colour sorted at a correctness rate of more than 99.90% on a machine. In MDS, the heading date of tested lines was advanced by 2~6 days. The outcrossing rate was improved by 8.59% and 7.61%, and the total panicle number increased by 4.78% and 5.80%, respectively. Ultimately, the actual yield in MDS significantly exceeded that in SST by 12.56% for P88S/G-4 and 8.95% for Y58S/G-15. This model succeeded in recycling hybrid seeds via color sorting and seems promising for decreasing labour inputs in hybrid seed production.

Keywords

• hybrid rice
• hybrid rice seed production
• red-hull line
• colour sorting
• direct seeding