Effect of soil moisture stress at booting and flowering stages on pollen development, pollination and fertilization in upland NERICA cultivars

Spikelet sterility induced by soil moisture stress during reproductive development greatly limits grain yield in upland rice. This study aimed to elucidate differences in responses to soil moisture stress for pollen development, pollination and fertilization among upland rice cultivars. A greenhouse experiment with a split-plot design was performed for five different soil moisture treatments (T1 to T5) as the main plots and three cultivars (NERICA 1, NERICA 4 and Yumenohatamochi) as subplots, each with three replicates. Plants in pots were grown under well-watered condition (T1) and various moisture stress conditions: moderate at the booting stage (T2), severe at the booting stage (T3), moderate at the flowering stage (T4) or severe at the flowering stage (T5). During the 9-day stress period, soil moisture was maintained at -10 to -20 kPa for moderate moisture stress or -20 to -49 kPa for severe moisture stress under controlled irrigation. NERICA 1 had fewer differentiated microspores and developed pollen grains in T2 and T3 and showed poorer anther dehiscence and fewer pollen grains on the stigma than did NERICA 4 and Yumenohatamochi. NERICA 4 showed a lower percentage of basal dehiscence in T4 and T5, causing fewer pollen grains to be deposited on the stigma than for NERICA 1 and Yumenohatamochi. The results indicate that the highly sensitive process of fertilization are pollen development in NERICA 1 and pollination in NERICA 4 under soil moisture stress