Effects of water deficit on physiology and morphology of three varieties of NERICA rainfed rice (Oryza sativa L.).

Water deficit is a major problem in rice grown under rainfed conditions. It affects plant growth and development and ultimately leads to a considerable yield reduction or crop failure. Although the rice crop is susceptible to water deficit, there is a marked genotypic variation in rooting pattern in rice in response to water deficit. Drought tolerant cultivars have deep and thick roots. The thick roots are positively correlated with xylem vessel area, which are vital to the conductance of water from soil to the upper parts of the plants to meet the evaporative demand. The objective of this experiment was to investigate the possibility that the three developed rainfed rice varieties referred to as, New Rice for Africa (NERICA) and coded as N2, N4 and N11 might reveal cultivars specific diversity in the regulatory mechanisms underlying their different responses to water deficit with a view of establishing the most drought tolerant rice variety that can be grown under rainfed conditions in Kenya. This study was carried out at the University Botanic Garden, Maseno, during 2005- 2006. Plants were subjected to water deficit treatments in the green house in a factorial set up. The seeds of the three NERICA cultivars of rice were planted in 20 Litre PVC pots in the greenhouse arranged in a randomized complete block design (RCBD) with four treatments and four replications. The treatments were irrigating once a day (control) and every 2, 4 and 6 days, respectively. The parameters measured included plant height, root length, plant biomass, transpiration and stomatal conductance rate. Plant height, plant biomass and root length reduced with a decrease in water content. The stressed plants had lower transpiration and stomatal conductance rates than the well watered plants in all the three varieties. In all the parameters measured N2 was least affected by the water deficit as compared to N4 and N11. Results indicate that N2 has superior physiological traits under water deficit hence may be recommended for growing under rainfed conditions in Kenya.