Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/19/2018
Publication Date: 10/16/2018
Citation: Gealy, D.R., Rohila, J.S. 2018. Field performance of an Indica x Tropical Japonica rice mapping population under AWD Stress. Proceedings of 37th Rice Technical Working Group Meeting, February 19-22, 2018, Long Beach, California. p 107. Electronic Publication.
Technical Abstract: Alternating-wetting-drying (AWD) is an emerging rice irrigation management system that has the potential ability to reduce both irrigation water use and emissions of the greenhouse gas, methane. Based on preliminary experiments, 15 (F10) recombinant inbred lines (RILs) showing diversity for root and shoot traits were selected for this study from a mapping population of ~330 RILs that was derived from a high-tillering, weed-suppressive indica (PI 312777) x a low-tillering, non-suppressive southern long grain tropical japonica (Katy). The selected RILs were evaluated in the field for their potential tolerance to ‘severe’ AWD stress conditions, with the goal of identifying RILs with AWD tolerance. The experiment was a split plot design with four replications. The main plots were conventionally flooded (FLD) or AWD irrigation, and subplots were the 15 diverse RILs and the parents. Seeds were planted 2 cm-deep in Dewitt silt loam soil in plots 4-m-long with 6, 18-cm-wide rows on May 9, 2017 near Stuttgart, AR. Weeds were controlled in all plots using commercially-available herbicides. All genotypes emerged on May 23rd. Plots were fertilized with 110 kg/ha N as urea and flooded on June 20th. After permanent flood had been established in all plots, drain cycles were initiated in the AWD bays. Due to unusually rainy and cloudy conditions in 2017, there were only two AWD drain/reflood cycles. These cycles occurred July 14/July 21-24 and July 28/Aug. 25. Leaf gas exchange parameters (photosynthesis, Pn; transpiration, E; and stomatal conductivity, C) in both AWD and FLD plots were measured using an infrared gas analyzer system when soil volumetric water content (VWC) had reached ~20-30% (less stress) or ~16-26% (more stress) in the AWD plots. Plots were then reflooded and the new AWD cycle begun. Agronomic measurements including plant height, and leaf area index (LAI) were recorded. Plots were harvested Oct. 4-17 and grain yields were determined. The RILs and parents were designated as stress-susceptible or stress-tolerant based on their relative yield reduction in AWD compared with FLD. In the first AWD cycle, at a time when visual stress symptoms were largely absent (July 21, 2017), AWD reduced C by up to 70% in stress-susceptible lines such as Katy and RIL90, compared with more stress-tolerant lines such as PI 312777 and RIL401, which were reduced by less than 40%. In the second AWD cycle, after susceptible plants had begun to exhibit visual stress symptoms such as wilting or curling leaves, large reductions also were observed for Pn in Katy, RIL90, and RIL15 (up to 80%) compared with the more tolerant genotypes, RIL401 and PI 312777 (less than 40%). Interestingly, the VWC of soil in plots of the highly AWD-stress-susceptible Katy parent was greater compared with that of AWD-tolerant genotypes such as the PI 312777 parent, and suggests that Katy may be relatively less able to extract water from soil as water deficits increase, and may be partly responsible for a negative correlation (r= -0.29 to -0.37) observed between VWC and gas exchange parameters. Root data gleaned from preliminary experiments appeared to be helpful in identifying some AWD-tolerant genotypes. The PI 312777 parent had spreading roots with numerous, long root hairs, and very high root mass (>2X) when compared with the Katy parent. The AWD-susceptible RIL90 had very few root hairs. The AWD-tolerant RIL401 had moderately hairy and spreading roots, and AWD-tolerant RIL12 had very high root mass (= that of PI 312777). AWD reduced the LAI and final height at harvest by 11% and 13%, respectively. Yields over all genotypes were 39% lower in AWD compared with FLD plots, and there was a genotype x irrigation interaction in which tolerant genotypes such as PI 312777, RIL401, and RIL12 had statistically similar yields in AWD and FLD, whereas yields of susc