High Temperatures Could Leave Seed Crops Sterile

Some crop plants—like rice, kidney beans, soybeans and peanuts—stop producing seeds when exposed to high temperatures. Agricultural Research Service (ARS) scientists in Gainesville, Fla., found that the higher temperatures affect reproductive processes in the plants.

Soil scientist L. Hartwell Allen, Jr., and plant physiologist Joseph C. Vu in the ARS Chemistry Research Unit at Gainesville carried out temperature-elevation studies with colleagues associated with the University of Florida-Gainesville and the International Rice Research Institute.

Increased temperatures affect reproductive processes more than they affect photosynthesis and vegetative growth, according to Allen. A plant may still grow to its typical size even if its seed development fails.

To evaluate heat tolerance of various cultivars, the scientists used growth chambers under natural sunlight and greenhouses for a range of temperatures. They measured heat’s effect on yields of rice, grain sorghum, kidney beans, soybeans and peanuts grown at two levels of carbon dioxide—350 parts per million (ppm), which is near current levels of atmospheric carbon dioxide, and 700 ppm—and at four maximum/minimum daily temperature cycles.

Each crop was found to have its own optimal mean daily temperature (OMDT) for seed yield. As temperatures rose, yields decreased, dropping to zero at about 18 degrees F above each crop’s specific OMDT. Seed productivity generally decreased by about six percent for every one degree F above a given plant’s OMDT, according to Allen.

For all the crops studied, even when pollination was successful, shortened seed-filling time and higher respiration rates at moderate temperature increases also contributed to yield declines.

Using traditional breeding to develop crops with built-in heat tolerance may offer the best hope for helping plants--and growers--cope with rising temperatures, according to Allen.

Read more about the research in the August 2006 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.