Using an enzyme from green algae, ARS researchers are exploring new ways of improving photosynthesis in soybean plants. Photosynthesis is the process by which plants use energy from sunlight to make their food—carbohydrates—from carbon dioxide (CO₂) and water. Rubisco is a key enzyme in the process because it captures CO₂ from the air. But in soybeans, rubisco sometimes also captures oxygen. This happens about 20 percent of the time, scientists estimate, keeping the plant from peak photosynthetic performance. That, in turn, can deprive the plant of more energy for growth and production of seed prized for their high-quality, edible oil and protein. Soybean crops now yield about 39 bushels per acre and generate $9.89 billion annually. But scientists believe an even higher seed yield can be achieved. In the lab, they're testing this theory by genetically replacing the natural rubisco of soybean plants with an enzyme from the green algae species Chlamydomonas reinhardtii. The latter's enzyme captures CO₂ more quickly, they found. If successful, their approach could mean transgenic soybeans with a more "selective" appetite for CO₂ instead of oxygen. Besides improved productivity, the enzyme-substitution technique might also help soybeans to exploit higher CO₂ levels associated with global climate change.

Photosynthetic Research Laboratory, Urbana, IL
Don Ort/Archie Portis, Jr., (217) 333-2093, d-ort@uiuc.edu/arportis@uiuc.edu

Tropical corn from Mexico and Central America could become an alternative cattle feed to sorghum in the South. Dairy cows ate so much more tropical corn silage that they produced 10 to 20 percent more milk than when fed sorghum. Silage is a fermented, moist feed for wintertime. In steers, tests of its nutritional value showed it to be slightly less digestible than forage-type sorghum. But the steers ate more of the tropical corn, evening out the digestibility difference. What's more, tropical corn yields about 87 percent more dry matter than sorghum, making each acre more productive. Farmers usually plant sorghum when it gets too wet or too late in the season to plant temperate corn. In the southern United States, where long days and a long growing season substitute for its native climate, tropical corn is a good alternative because it grows well in heat and tolerates insects. Its season: Plant in June, harvest in October. Alternating tropical corn and a winter crop for ensiling in the spring—such as winter wheat or barley—would protect the ground from erosion and give cows two quality feeds. ARS plans to work with a university economist to see if this approach would produce extra money for farmers. If so, it might become an even more attractive alternative to sorghum.

Plant Science Research Unit, Raleigh, NC
Joseph C. Burns, (919) 515-7599, jburns@cropserv1.cropsci.ncsu.edu

Farmers on the 20-million-acre Central Great Plains are finding that alternative rotations can be 20 to 40 percent more profitable than the traditional wheat-fallow system. ARS researchers are testing 20 dryland crop rotation and tillage systems, seeking the best alternatives to wheat-fallow. In wheat-fallow, growers plant one crop every other year and leave the soil bare for a year to store water. Now, some farmers are growing more—and different—crops that are more water efficient. Wheat-fallow systems use only 40 percent of the average 14 to 18 inches of annual rainfall, but continuous cropping can soak up nearly 80 percent. Researchers have found that growers can successfully crop continuously in years with normal or more precipitation by using a cycle of four crops and alternating high- and low-water-use crops. For example, compared to wheat-fallow, farmers can double the land's productivity with a rotation of wheat, corn, proso millet, and—as the fourth component—field peas, another wheat crop, or fallow. This approach still provides for the crops' water needs, and the crop diversity encourages soil microbes that make the farming ecosystem more sustainable over the long haul. The researchers have improved water use so well, they're nearing their goal of a crop every year. They're still working on rotations that succeed in dry years. Options include a forage crop and green fallow, which use less water than wheat, corn, millet, and sunflowers.

Central Great Plains Research Station, Akron, CO
Randy L. Anderson, (970) 345-2259, rlander@lamar.colostate.edu

An intensive 3-year survey found that at least 635 different species of Lepidoptera (moths and butterflies) inhabit the Marine Corps Air Station Miramar in San Diego County, CA. Information from the survey of the approximately 23,000-acre air station will be used by insect identifiers, taxonomists, ecologists, integrated pest management specialists, conservationists, and biological resource managers. Lepidoptera play an important role in pollination. Many of them are economically important pests of crops and ornamentals, and the adults and larvae provide food for countless other invertebrates as well as larger animals. Among the species documented during the survey were at least 12 moths previously unknown to science. In addition, scientists found one butterfly (Lycaena hermes or Hermes copper) that is recognized as "sensitive" and declining by the U.S. Fish and Wildlife Service. Two moths—Dryadaula terpsichorella and Metapluera potosi—had never before been found in the United States. The survey was conducted from October 1995 through September 1998 and orchestrated by an ARS scientist. Sampling methods included blacklight trapping for 364 nights, daytime collecting for 148 days, and pheromone baiting. It's likely the air station's lepidopterans are even more diverse than the scientists have documented; they estimate that, in all, nearly 700 to possibly more than 900 species call the station home. Inventories such as this document the rich biological heritage of the United States.

Systematic Entomology Laboratory, Washington, DC
John B. Brown, (202) 382-1778, jbrown@sel.barc.usda.gov

Fumigating walnuts with sulfuryl fluoride kills any codling moths or navel orangeworms that would like to hitchhike on the freshly harvested nuts. The chemical might replace the methyl bromide fumigant now being used but is slated for withdrawal from use by 2005. ARS scientists at Fresno, California, are the first to show the potential of sulfuryl fluoride as a methyl bromide alternative for fumigating walnuts. Sulfuryl fluoride fumigation might help America's walnut growers keep European sales strong. European Union nations are key importers of American walnuts, but they currently require methyl bromide fumigation of the shipments. Unlike methyl bromide, sulfuryl fluoride is not thought to contribute to depletion of Earth's protective ozone layer. Sulfuryl fluoride is already approved as a structural fumigant but is not yet OK'd for food uses. By exposing lab-reared codling moths and orangeworms to vacuum-chamber fumigation, the scientists found that using slightly more than 0.001 ounce of sulfuryl fluoride per liter of air kills these insects. Other fumigation experiments, using some 2,500 walnuts artificially infested with codling moths in their wormlike larval stage, indicated that using seven times less sulfuryl fluoride than methyl bromide killed 100 percent of the codling moth larvae. The Walnut Marketing Board helped fund the research.

Horticultural Crops Research Laboratory, Fresno, CA
J. Larry Zettler/James G. Leesch, (559) 453-3000, lzettler@qnis.net/jleesch@qnis.net