Go back to JSRRweb homepage:ホームページへ戻る
Kamoshita, A.1, L.J. Wade1, T.Azhiri-Sigari1 and A.Yamauchi2
1: Agronomy Plant Physiology and Agroecology Division, IRRI,
Philippines
2: School of Agriculture Science, Nagoya University, Japan
Introduction
Rice production in rainfed lowland environments often encounters early season drought, which sometimes makes plants unable to recover and causes yield reduction. Genotypic variation in drought recovery, which is often observed in drought nurseries by plant breeders, is a putative trait to increase yield in drought-prone rainfed lowland rice growing areas (Fukai and Cooper 1995). However, there are not many studies to examine physiological basis for this genotypic variation, particularly those taking into accounts both root and shoot response to drought and rewatering. This study aims to elucidate the underlying mechanisms of genotypic variation in drought recovery of rice seedlings after imposition of mild water stress.
Methods
The pot experiment was conducted in greenhouse at IRRI from March to May 1997. The choice of lines, experimental design, soil type, pot size and other measurements were same as the previous study by Azhiri-Sigari et al. (1997). Eight rice lines were grown at tillering stage in both well-watered and water stressed conditions. The water was withheld from 21 days after sowing until ca. 4 kg of water was extracted from soil. Pots were rewatered thereafter for 9 days. Dry weights of shoot and leaf, and root length at shallow (0-10cm) and deep (30-50cm) soil layers were measured at the end of stress and at 9 days after rewatering.
Result and Discussion
There was genotypic variation in biomass produced during the 9 days of rewatering period (12-19 g plant-1) among 8 rice lines in stressed treatment. Lines such as Namsagui19 and KDML105, which extracted ca. 4 kg of soil water within shorter duration (18 and 19 days, respectively) during water-withholding period, showed better recovery, compared with the lines with longer extraction time, such as IR20 and IR62266 (21 and 23 days, respectively). Namsagui19 and KDML105 had longer root length in deep soil layers at the end of stress period, being able to utilize water in deep layers after surface soil water was depleted. IR20 and IR62266, because of the lack of deep root system, had to extract water only from surface soil layers with lower water content, resulting in slower water extraction. The partitioning of biomass to leaf was smaller in IR20 and IR62266 (37%) than in Namsagui19 and KDML105 (42%) in stressed treatment. CT9993 had deep roots at the end of stress, but it had smallest proportion of leaf after rewatering, and not resulting in better recovery.
This study thus pointed the importance of combination of deep root system and biomass distribution to leaf for superior drought recovery of rice seedlings when water stress gradually developed at tillering stage. Better recovery of KDML105 was consistent with the results of Azhiri-Sigari et al. (1997), in spite of the difference in the timing and intensity of water deficit.
References