Profiling the physiological response of upland and lowland rice ( Oryza sativa L.) genotypes to water deficit

One of the most promising alternative methods to reduce water consumption is the aerobic rice production system, which was originally developed for a non-saturated soil. To evaluate rice genotypes; (three upland, two lowland irrigated and 10 aerobic) under well watered and water deficit condition, an experiment was carried out in a complete randomised design with three replication at the University of Guilan, Rasht, Iran, in 2016. Soil water content was monitored as a fraction of transpirable soil water (FTSW). Based on the results, response thresholds of relative leaf expansion (RL) and relative transpiration (RT) of rice genotypes quantified as 0.48–0.73 and 0.2–0.58, respectively. Upland genotypes and Neda cultivar had cooler leaves than other genotypes under water deficit conditions. The relative water content (RWC) varied among genotypes with an almost similar trend. In all rice genotypes, the RWC between FTSW = 1 to about FTSW = 0.4 was almost constant. Water deficit conditions led to decreased chlorophyll fluorescence parameters in all rice genotypes, including Fm, Fv and Fv/Fm. Along with water stress severity, F0 and Fv/F0 were also increased. The RL and RT responses in aerobic genotypes, that responded rapidly, were delayed in lowland and upland genotypes. Irrigation programs using modelling and decision support in rice seem to be more reliable and practical when considering parameters such as leaf expansion, transpiration and RWC response thresholds.