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Interaction of chilling and light in limiting rice production

Overview of Project

Overview Objectives

Chinese scientists consider environmental stress to be the most important constraint on rice yield in South China, where two consecutive crops are grown each year. In the first crop, chilling temperatures cause death or damage of young plants. Late in the second crop they reduce grain weight. And in both crops low light levels caused by prolonged cloud cover during important stages reduce the growth rates. Currently available early-maturing rice varieties could avoid some second-crop damage, but have low yields.

The project will involve collaborative studies with rice research centres in South China to apply Australian-developed rapid methods for measuring chilling tolerance to the identification of promising breeding material. The scientists will also investigate the role of light as a critical interacting factor in chilling stress in rice, and the relations between low solar light and yield.

To analyse plant temperatures and canopy microclimates during natural chilling events in South China, the project will install equipment to measure: temperature and light regimes in seedling nurseries; plant temperatures during natural chilling events after transplanting of the first crop; light environment of flag and canopy leaves post-chilling; and the coincidence of high light intensity and low temperatures in both crops.

The CSIRO members of the team have developed a method of screening for chilling tolerance by chlorophyll fluorescence, which declines progressively during chilling at a rate that correlates inversely with chilling tolerance. The method is quick, can quantify the tolerance, measures living plant tissue non-destructively, and uses relatively low-cost portable equipment. Comparative measurements have established its validity on a wide range of plants, including rice and other grain crops, vegetables and fruits.

Scientists at the Rice Research Institute will continue a field program of selecting for cold tolerance in the second rice crop, which currently involves 565 local and 260 imported varieties. As selection criteria, they use chilling-induced sterility (measured by the proportion of unfilled grains at harvest) and the chilling effect on photosynthesis leading to reduced grain fill (measured by the weight per thousand ‘filled’ grains). Research in Australia will apply the chlorophyll fluorescence method to further screen the Institute selections, together with some from other sources, and will attempt to correlate the results with the chilling responses measured in the field. Preliminary experiments in Canberra suggest good correlation, and these will be extended in detail by comparing fluorescence measurements with soft X-ray analysis of panicle development as well.

The scientists will study both the development of chilling injury and recovery from it, in the absence of light. In addition to the new method, they will use gas exchange measurements and estimates of survival and relative growth rates of survivors. Comparisons between rice cultivars of differing tolerances will establish the time-temperature relations causing damage and the relative importance of the injury and recovery phases.

Other experiments will determine the relative abilities of rice cultivars to chill-harden when grown in a cool environment. Bright sunlight following chilling at night causes additional and severe damage due to photoinhibition. A detailed study of this interaction between chilling and light will begin immediately, with a limited number of genotypes. The scientists will attempt to determine the biochemical basis of photoinhibition, its importance for crop yield and the critical temperatures and light intensities.

Following from that study, they will examine low light intensity as a potential factor limiting rice production in South China. The need to persevere with short varieties which better withstand typhoon damage severely restricts the option to increase light capture by selecting for physical changes in plant structure; moreover, varieties selected to withstand high light intensities after chilling may be poorly adapted to make use of low intensities. However, methods devised for measuring photoinhibition may also provide a basis for selecting plants with enhanced light-capturing capacity.

The project should benefit breeding and selection programs not only for rice but for other chilling-sensitive crops, such as litchis. Results obtained, and the rice cultivars selected, should prove useful in other rice-producing countries."

Project Dates

10 Jul 1986 - 09 Jul 1989

Partners

CSIRO Division of Food Science and Technology - Australia
Rice Research Institute - Guangzhou - China
South China Institute of Botany - China
Australian National University - Australia

Website
Launch Website