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Azhiri-Sigari, T.1, L. J. Wade1 and A. Yamauchi2
1:Agronomy, Plant Physiology and Agroecology Division, IRRI,
Philippines
2:School of Agriculture, Nagoya University, Japan
Introduction
Although root traits are often considered important for drought avoidance, it is not clear whether they contribute to enhanced extraction of soil water during drought under rainfed lowland conditions (Wade et al.1997). A greenhouse experiment was conducted at IRRI in the 1995 dry season to examine genotypic variation in root characteristics of eight rainfed lowland rice lines under well-watered and water deficit conditions.
Methods
Eight lines (CT9993, IR52561,IR58821, IR62266, KDML105, Mahsuri, Namsagui19, IR20) were subjected to two water regimes in a split-plot design where water regimes were assigned as main plots and lines as subplots. In well-watered treatments, pvc pots (20cm diameter, 50cm depth) were continuously watered, while in stressed treatments, water was withheld from panicle initiation (PI) until leaf rolling score of 5 were attained, then pots were rewatered. Planting was staggered in order that PI among varieties coincide. Other experimental details were documented in Azhiri et al. (1996, 1997).
Results and Discussion
With water deficit, root length density (RLD) was similar to well-watered in surface layers, was reduced at 10-20 and 20-30 cm depths, and was greater at 30-40 and 40-50 cm depths. A similar pattern was observed for root mass density . Root thickness was less at 5-10, 10-20 and 20-30 cm soil depths but was substantially more at 40-50 cm soil depth. Because of the severity of the drought stress imposed RLD failed to recover on rewatering, except for the earlier line (CT9993). Transpiration partly recovered for CT9993, KDML105, and Namsagui19, which may imply that the Thai lines (KDML105 and Namsagui19) were able to maintain a more functional root system in these conditions.
References