Dry Weight Accumulation, Root Plasticity, and Stomatal Conductance in Rice ( Oryza sativa L.) Varieties under Drought Stress and Re-Watering Conditions

Drought is one of the main factors limiting rice (Oryza sativa L.) productivity and has become an increasingly severe problem in many regions worldwide. Establishing breeding programs to develop new drought-tolerant varieties requires an understanding of the effect of drought on rice plants and the mechanisms of drought tolerance in rice. We conducted a pot experiment to explore growth characteristics, root plasticity, and stomatal conductance in six rice varieties (DA8, Malagkit Pirurutong, Thierno Bande, Pate Blanc MN1, Kinandang Patong, and Moroberekan) in response to different drought stress and re-watering conditions. Drought stress significantly depressed plant growth, root size, and stomatal conductance in all experimental varieties. These negative effects depended on both the variety and the severity of the drought stress treatment. Under moderate drought stress (10 days after drought treatment), growth was less influenced in roots than in shoots. In contrast, there was an opposite trend under severe drought stress (15 days after drought treatment), with growth being more severely affected in roots than in shoots. Rice plants recovered from drought stress in terms of dry matter accumulation, root size, and stomatal conductance after re-watering; however, the recovery pattern differed among varieties. DA8 exhibited the highest dry weight accumulation and root size (root length, root surface area, root volume, fine root length, and thick root length) under well-watered, drought stress, and re-watering conditions. Kinandang Patong showed the highest recovery ability in dry matter accumulation, root length, root surface area, and stomatal conductance after re-watering. Malagkit Pirurutong expressed the poorest recovery ability in dry matter accumulation after re-watering. These three varieties might be selected for further experiments focusing on the mechanisms of drought tolerance and recovery ability in rice.