As researchers zero in on genetic advances that will give crops resistance to heat, drought, flooding, and other climate-related factors, farmers will have even more options for coping with adversities built in to the seed they plant.

Among the discoveries already in the pipeline:

• Scientists at Norwich, England, have isolated a “thermometer” gene that plants use to sense temperature.

Working with a mustard plant, they spent five years developing a mutant that had lost its ability to react to high temperatures — it grew as if the temperature were ideal. This gene could, within 10 years, allow development of crop plants that would better tolerate rising global temperatures or, conversely, to make them more tolerant of cold.

If temperatures continue rising, the scientists say, it could have a significant adverse effect on crop productivity. By manipulating genes within plants such as rice and wheat, which are sensitive to high heat during their growth process, they hope to lessen the impact on yield.

• USDA researchers, who say that year-in, year-out, the factor that most adversely affects farmers’ pocketbooks, is drought, are developing crop plants that will grow and yield under arid conditions.

This not only would allow growers to obtain satisfactory yields, but could reduce the amount of water used by agriculture for irrigation — now 60 percent or more of the fresh water from lakes, rivers, and other sources.

• Rice varieties genetically engineered for flood tolerance are being adopted at a rapid rate in flood-prone areas of India, enabling growers to produce crops in areas of low productivity. Within a year of its release, the high-yielding rice variety is being grown by more than 100,000 Indian farmers.

While rice grows quite happily in flooded fields, if the plants are wholly submerged, they are deprived of oxygen and can die within only a few days.

University of California, Davis Professor Pamilia Ronald and her colleagues isolated a gene that will allow plants to withstand submergence for as long as two weeks. It was transferred to commercial varieties, and now farmers are getting three- to five-fold yield increases.

Three of the most important U.S. crops — cotton, soybeans, and corn — are predicted to suffer declines in production as much as 80 percent if temperatures continue to rise as projected in coming years.

The study by Wolfran Schlenker, Columbia University School of International and Public Affairs, and Michael Roberts North Carolina State University, shows yields for the three crops initially increasing gradually as climate warms, but then dropping precipitously after reaching their temperature ceilings.

Their findings indicate temperature increases are beneficial only up to about 86 degrees F., after which current crop varieties become more sensitive to heat. “This study shows temperature extremes are not good,” Roberts says.

Were such declines in crop production to occur, it would have global repercussions, the authors say, because many developing countries depend on food exports from the U.S.