Application of the pressure chamber method to evaluate root hydraulic conductance in rice plants with tillers

The root hydraulic conductance of rice is often measured using the pressure chamber method only for the main stem at the seedling stage, as it is difficult to evaluate at a more advanced growth stage with tillers due to the high risk of pressure leakage from the gaps between the tillers. The aim of this study was to identify techniques that are effective for prevention of air leakage and an improvement in the success rate of root hydraulic conductance measurements in rice plants with tillers. Using three rice (Oryza sativa L.) genotypes, FR13A (aus), KDML105 (indica), and Swarna (indica), the root hydraulic conductance of the main stem and four tillers were calculated using the pressure chamber method at 98, 104, and 95 days after sowing, respectively, using the following three techniques: 1) careful detachment of dry leaf sheaths, 2) ensuring spacing between tillers and an appropriate amount of silicone in the socket, and 3) pre-fixing the socket to prevent vertical misalignment. Using these three techniques, we achieved a success rate of 92.8% (13 of 14 plants) for root hydraulic conductance measurements in the genotypes. Additionally, we show that genotypic variation in root hydraulic conductance exists at the late vegetative stage, and that the growth stage can have a significant effect on root hydraulic conductance values. In conclusion, this study presents a detailed pressure chamber method for measuring root hydraulic conductance in rice plants with tillers, reducing the risk of pressure leakage, and improving the success rate of the measurement.