Effect of soil water potential on grain quality at different spike positions during grain filling in rice

This study investigated the effects of soil moisture stress during grain filling on the quality of grains at different rice spike positions. Two rice cultivars, “Yangdao 6” (indica) and “Yangjing 9538” (japonica), were pot-grown and subjected to four soil moisture treatments (0 kPa, -15 kPa, -30 kPa, -45 kPa) during post-anthesis grain filling stage. The study showed that soil moisture condition during the grain filling greatly influenced grain quality. The sensitivity of grain quality to soil moisture varied with cultivar and grain position within the panicle. Compared with 0 kPa (CK) soil water potential, milled rice rate, head milled rice rate and breakdown value at an increased rate under moderate dry soil treatment (i.e., soil water potential of -15~ -30 kPa). However, the degree of chalkiness and setback value decreased. Grains from secondary branches were more obviously affected than those from primary branches. Furthermore, moisture stress had greater effect on grains that flowered late than those that flowered early in the same branch. Rice quality also worsened with decreasing soil water potential. As soil water potential dropped from 0 kPa to -45 kPa, crude protein content and gel consistency increased. The results suggested that moderate dry soils with water potential of -15 ~ -30 kPa at grain filling enhanced grain formation and rice quality.