Alteration of dry matter accumulation under soil moisture fluctuation stress in rice (Oryza sativa L.)

Drought-flood abrupt alterations (DFAA) is a condition in drought season when sudden rain inundate rice plants. These events are due to the high frequency of extreme climate events that might pose a threat to rice productivity. DFAA causes cumulative stress on rice which affects crop growth and alters dry matter accumulation. This study aims to understand the effect of DFAA to dry matter accumulation by assessing six rice varieties under DFAA. Three treatments were provided such as continuously irrigated as non-water stress (NS) as a control; drought to water stress -35 kPa (DFAA1) followed by sudden flood; drought to severe water stress -70 kPa (DFAA2) followed by abrupt floods; repeated until harvest. The study found that the alteration of dry matter accumulation was determined by root length, root weight, shoot length and shoot weight. Only varieties that are able to increase root depth under water stress fluctuation will be able to maintain the yield. The results of study showed that root depth was positively correlated with shoot length (r = 0.68), shoot weight (r = 0.62), root weight (r = 0.57), percentage of filled grain (r = 0.55) and number of filled grain per hill (r = 0.49). Shoot length was positively correlated with shoot weight (r = 0.83), root weight (r = 0.75) and the number of filled grain (r = 0.62), while shoot weight was only positively correlated with root weight (r = 0.88). This means that only root depth and shoot length can increase the seed setting rate and the number of filled grains per hill. Furthermore, at DFAA2, the percentage of filled grain was highest in Sipulo followed by Bo Santeut, Sanbei, Towuti and Situ Patenggang, which mean that varieties with deeper and heavier root dry weight can maintain higher yields than shallow and low root dry weight. The result of the study may allow to select rice varieties that are resistant to multilevel water-stress and able to maintain the potential yield, by looking at root depth, root dry weight, and through their grain yield in general. These traits could become key indicators for resistance to DFAA stress in rice. It is also necessary to pay attention to the fluctuation of soil water content in critical phases, especially in the reproductive phase and grain filling