Relative water content, water potential and transpiration of Africa rice (Oryza glaberrima) were investigated in a controlled condition under phytotron. Two Oryza sativa cultivars, IR55423-01 (a drought tolerant genotype) and IR64 (drought sensitive genotype) and 8 O. glaberrima accessions were grown under droughted and watered conditions. The fraction of transpirable soil water (FTSW) was used as an indicator of water availability. Transpiration was determined by changes in daily pot weights and the ratio of transpiration of droughted to watered plants expressed as normalized transpiration ratio (NTR). The FTSW was greater in O. glaberrima accessions CG14, RAM118 and RAM 152 than all the O. sativachecks; suggesting that they might have the capacity to close their stomata earlier in response to drought stress, in other to keep transpiration rate similar to the rate of uptake of soil water resulting in maintenance of the water balance of the plant. RAM 3 had the greatest dehydration tolerance and some accessions such as RAM 134, RAM152 and RAM163 had lower dehydration tolerance than RAM 3, CG 14 and IR55423-01’ but survived longer suggesting that other avoidance mechanisms such as leaf movement and reduction of leaf area complemented these traits and enhanced their survival. In general, it is necessary to keep FTSW above 0.53, in order to keep transpiration and plant water status high in preventing reduction in dry matter production which will lead to higher yields.
Key words: Drought tolerance, O. glaberrima, O. sativa, fraction of transpirable soil water (FTSW), dehydration tolerance
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