Root system development and dry matter production of PhilRice germplasm under various water-deficit stress intensities

Drought stress at various intensities leads to significant reductions in rice yield especially in rainfed lowland and in irrigated lowlands with inefficient irrigation system. The Philippines has diverse rice genetic resources which is a vital component in rice breeding program serving as potential sources of gene(s) for tolerance to abiotic stresses such as drought. In this study, the authors evaluated 48 PhilRice germplasm materials under different intensities of drought stress by using the Line Source Sprinkler (LSS) system. The LSS concept creates soil moisture gradient in which the plant near the line source received more water (wet) while the farthest received less water (dry). Each germplasm material was planted perpendicular to the line source with distance of 20 cm between rows and 45 cm between hills in a watertight experimental bed under rain or shelter. The experiment was laid out in RCBD with two replications. The drought stress was imposed at 14 days after transplanting by draining the water. Soil moisture sensors were placed at both sides of the seedbed at varying distances (10, 50, 90, 130 and 170 cm) from LSS. Eight genotypes showed 5-11% increase in shoot dry weight (SDW) under mild drought (13-15% MC) relative to well-watered (22% SMC) condition. In contrast, these genotypes showed 49-66%, reduction in SDW under severe drought (8%-12% SMC) condition. Furthermore, the performance of these eight genotypes was validated under different water stress conditions using the soil-filled rootbox system. Among the eight genotypes, PRR1000593 Belibod showed loss reduction in SDW (39.7%) under progressive drought (PDR, 10% SMC) and even increase its SDW (77.6%) under fluctuating soil moistures (transient waterlogged-to-drought condition). Such responses in dry matter production in Belibod under PDR and fluctuating soil moisture were contributed by its ability to maintain greater root system development.