Warming Puts the Freeze on Seed Yield (to a Degree)
By Jim Core
November 1, 2002
While research on the effects of
greenhouse gasses continues, studies by Agricultural Research Service scientists
and others show that higher carbon dioxide levels increase forage crop yields
over a range of temperatures--and seed crop yields when temperatures are
optimal. But research also shows that the global change some are predicting
could leave seed crops partly sterile.
The threat to cereal grains and legumes is the potential rise in
temperatures, according to L. Hartwell Allen, Jr., a soil scientist in the ARS
and Environmental Research Unit, Gainesville, Fla.
Seed productivity decreases about 10 percent for every 2 degrees Fahrenheit
the temperature increases above ideal levels, according to Allen. But
photosynthesis and plant size are little affected until much higher
temperatures are reached. Even when seed development fails, the plant may still
grow to its typical size.
In elevated-temperature studies, pollination of individual flowers either
fails completely or, when fertilization is successful, seeds of some crops
develop poorly. For example, soybean yields are reduced because fewer seeds are
produced, and individual seeds weigh less.
Allen and ARS plant physiologist Joseph Vu, University of Florida crop physiologist Kenneth
Boote, and postdoctoral scientist Vara Prasad found that several physiological
functions related to reproduction and pollination fail as temperatures
increase. Abnormally high temperatures during the 2- to 3-week pollination
season could affect seed development at exactly the wrong time in a plant's
Traditional breeding could help if scientists locate wild relatives--or even
current cultivars--that produce high seed yields in very hot environments and
incorporate their tolerance into otherwise productive varieties. Cultivars that
shed pollen earlier in the day, when temperatures are cooler, would be more
likely to flourish, according to Allen. Recent ongoing research indicates that
some high-temperature tolerance does exist in certain rice cultivars. Genetic
engineering could help scientists introduce desirable genes from other plants.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.