Sensitivity of Pollination to Water Deficits at Anthesis in Upland Rice

Rice ( Oryza sativa L.) subjected to water deficit during anthesis shows pollination abnormalities resulting in low grain yields. To understand the mechanism of stress‐induced poor grain filling in relation to disturbed pollination, upland‐adapted cultivars were grown under controlled conditions. A 7‐day irrigation‐withholding period (Exp. 1) induced −1.7 and −2.0 MPa flag leaf water potentials (Ψ) in ‘Kinandang Patong’ and 63–83, respectively. A stress protocol for 7 d at anthesis achieved stress intensities of −0.4, −0.8, −1.1, −1.4, −1.7, −2.0, −2.3, −2.5, and −2.8 MPa in 63–83 and IRAT13 (Exp. 2). On the last day of the water‐deficit stress period, anther dehiscence of spikelets, pollen shedding, viability, germination, and spikelet sterility (at plant maturity) were measured. In each upland cultivar tested, low Ψ reduced pollen shedding capacity and germination. Dehiscence of anthers correlated with flag leaf Ψ ( R 2 = 0.944** [significant at P = 0.01] [IRAT13] and 0.987** [63–83]). Up to a stress intensity of Ψ1.4 MPa, more than 80% of anthers dehisced. Below −2.0 MPa, more than 60% of pollen grains did not dehisce. Pollen shed, total pollen per spikelet, and spikelets with more than 20 pollen were all directly related to Ψ. Pollen germination in vivo and germination per spikelet correlated linearly with water stress intensity. Significant deleterious effects on pollen viability at low water potentials were noted. All measured pollination traits accounted significantly for increases in unfilled spikelets at severe stress intensities. Thus, to ensure pollination success and spikelet fertility, responses of upland rice genotypes to a water deficit at anthesis could be evaluated using anther dehiscence, pollen shedding, and pollen germination in controlled conditions.