Genotypic differences in root hydraulic conductance of rice (Oryza sativa L.) in response to water regimes

To determine water uptake by rice in water-saving culture, we examined root hydraulic conductance (L₀), plant growth, and root anatomy of three rice genotypes (Oryza sativa L. ssp. indica cv. Beodien, traditional upland; ssp. japonica cv. Sensho, traditional upland; ssp. japonica cv. Koshihikari, improved lowland) under three water regimes: water-saturated (hydroponic), well-irrigated aerobic (control), and water-saving aerobic in soil. In hydroponic culture, although shoot dry weight (SDW) and root number were the largest in Sensho, root L₀ was the highest in Koshihikari. There was no significant relationship between root L₀ and SDW in hydroponics, so root L₀ might not limit shoot growth under flooding. Root L ₀ was much less in soil than in hydroponics, and that of Koshihikari was the lowest, especially in water-saving conditions. Root L₀ was highly correlated with SDW under water-saving conditions but not in the control, so root L₀ limits shoot growth under repeated water stress. Root anatomy was less affected by water regime than root L₀ and is genetically controlled. Thus, root L₀ may be more affected by water channels than by root anatomy.