Response of a U.S. rice hybrid variety to high heat at two CO2 concentrations during anthesis and grainfill

Authors: Fleisher, David; Barnaby, Jinyoung; LI, SANAI - Us Forest Service (FS); Timlin, Dennis

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2022
Publication Date: 6/17/2022
Citation: Fleisher, D.H., Barnaby, J.Y., Li, S., Timlin, D.J. 2022. Response of a U.S. rice hybrid variety to extreme heat and varying CO2 concentration during grain filling. Agricultural and Forest Meteorology. 323. https://doi.org/10.1016/j.agrformet.2022.109058.
DOI: https://doi.org/10.1016/j.agrformet.2022.109058

Interpretive Summary: Growing season air temperature has increased in rice production areas in the United States. This includes a heightened risk of an extreme temperature event, including high heat during rice flowering, to occur. This is problematic because such events reduce rice yield and grain quality which affect marketability for growers. Projected changes in temperature and carbon dioxide concentration may worsen this challenge. Hybrid rice varieties are widely used in the U.S. because of higher yields and may be able to better resist high heat. An experiment was conducted to evaluate this response for a popular hybrid cultivar. The study showed that grain quality will substantially decrease when temperature during flowing increase just a few degrees above normal for a few days. Yield also declined up to 50% compared to a control treatment. Higher carbon dioxide concentration could not minimize this heat stress effect. The reasons for yield loss were due to reduced pollination and grain weight. These results were the first to look at extreme heat effects on hybrid varieties in the U.S. and suggest research on heat stress avoidance strategies and new heat tolerance cultivars are needed.

Technical Abstract: Changing climate conditions are influencing quality and yield of the United States rice (Oryza sativa L.) export industry. The occurrence of extreme heat during grain filling, along with rising atmospheric carbon dioxide (CO2), is of particular concern for as-yet uncharacterized hybrid varieties. In this study, a popular rice hybrid was grown in soil-plant-atmosphere-research (SPAR) chambers under two growth CO2 levels and subjected to one of three day/night temperature regimes during grain-filling: a control temperature (T) (0C) of 28/22°C, and a +4 degree (4C) or +8 degree C (8C) increase. There was little difference in biomass between 0 or 4C levels; however, yields at the 8C level declined by over 50%, at a rate of about 0.83 or 1.0 tons per hectare per degree C for ambient or elevated CO2 grown rice, respectively. There was little difference in fraction of biomass allocated among leaf, stem or panicle at 0 or 4C, but the proportion to the panicles declined by about 31% at 8C. Total productive tiller numbers and grain fill percentages were similar across CO2 levels at each T treatment such that yield declines were associated primarily with a decrease in percentage grain fill, grain number, and mass. Slightly higher values for yield and harvest index were observed under elevated CO2 at the 3 T levels which was attributed to an average 0.1 g per 100-kernel increase in single grain weight. An interaction of CO2 and T on chalk content was observed, with expression at the +4C treatment 11% higher for elevated versus ambient CO2; however, chalk expression was similar for CO2 levels at the +8C treatment. Breeding efforts associated with climate resiliency should consider traits associated with hybrid vigor as well as high temperature resistance for grain sterility and quality factor responses.