Extension Ag Update
November/December 2003
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Latest Discovery Provides New Hope for Soybean Growers

Anne Dorrance, Plant Pathologist, (330) 202-3560, dorrance.1@osu.edu, written by: Candace Pollock, (614) 292-3799, pollock.58@osu.edu, News and Media Relations Ohio State University

Another research breakthrough has been made in the battle against Phytophthora sojae, a disease that can kill soybean plants and cause significant yield losses. Ohio State University researchers have discovered two previously unmapped locations on a soybean plant’s chromosome related to partial resistance of Phytophthora. The news means that new partial resistant genes wait in the wings to be identified for use in developing disease-resistant soybean packages for breeders and producers. It’s the first time new areas of partial resistance have been identified in soybean cultivars. “This is very exciting news. These loci are totally unrelated to anything previously identified, and the discovery opens up all types of resistance possibilities in the battle against Phytophthora,” said Anne Dorrance, a plant pathologist with the university’s Ohio Agricultural Research and Development Center in Wooster, Ohio.

Protecting soybean plants against Phytophthora sojae involves two types of resistance: single-gene resistance and partial resistance. Last year, OARDC researchers announced the discovery of a new single-resistant gene, labeled Rps8. The new gene is among a handful of single-resistant genes that work by killing the pathogen before it ever has a chance to establish in the plant.

“As Phytophthora colonizes the soybean plant, it’s secreting proteins. Somehow that protein is detected by the resistant gene. The gene then sends a signal and the cells around where that Phytophthora is colonizing all die, thus, killing the Phytophthora right where it is. So you’ve got this little area of necrosis and that’s as far as the infection goes,” said Dorrance.

However, if the pathogen is not detected by the resistant gene, then that gene becomes ineffective and the plant succumbs to disease. It’s the reason why so many single-resistant gene packages, specifically Rps1a, Rps1b, Rps1c, Rps1k, Rps3a, and Rps6, are no longer able to control Phytophthora in many Ohio soybean fields. “If the R-genes work, then you’ve got total control. But if they don’t work, then growers are out of luck in stopping Phytophthora,” said Dorrance, adding that partial resistant genes are much more of an important discovery than single-resistant genes.

Partial resistant genes allow Phytophthora to colonize a soybean plant, but only to a certain extent — keeping the disease at bay and preventing it from killing the plant as long as resistance is high enough. One advantage of partial resistant genes is that, unlike single-resistant genes, they are not race specific — meaning that partial resistance works against any Phytophthora isolate that exists. The result is partial-resistant soybean cultivars that yield consistently, no matter what race of Phytophthora may be present in a particular field.

“The benefit of partial resistance is it doesn’t make any difference what your race structure is. It doesn’t make any difference what isolate is used,” said Dorrance. “So when that partial resistant score is given to the seed companies they know that whatever field the soybeans are planted in, the partial resistance is going to work and it’s not going to change over time.”

The multiple genes involved in partial resistance aid in halting the disease, thus increasing the plant’s durability and providing protection over a longer period of time. Whereas a single-resistant gene could provide protection anywhere between 15 or 20 years, partial resistant genes alone, or combined with a single-resistant package, could mean protection against Phytophthora indefinitely.

Performance of Organic and Conventional Cropping Systems in an Extreme Climate Year

Lotter D.W., Seidel R., and Liebhardt W., The Rodale Institute 611 Siegfriedale Rd. Kutztown PA 19530. Published: American Journal of Alternative Agriculture, September 2003, vol. 18, no. 3, pp. 146-154(9).

For more than 20 years The Rodale Institute Farming Systems Trial has had three replicated cropping systems, one organic manure based (MNR), one organic legume based (LEG) and a conventional system (CNV). During this time, five drought years have allowed a comparison of sustainable and conventional cropping systems during dry seasons. The 1999 severe drought resulted in significant yield differences. Organic corn yielded 30% (LEG) and 137 % (MNR) compared to the conventional corn system. Organic soybeans yielded 196%(LEG) and 152% (MNR) relative to the conventional soybean system. Higher water holding capacity in the organic systems is believed to be the reason for these yield differences.

Helping Stored Alfalfa Keep Its Protein


Erin Peabody, ARS News Service, Agricultural Research Service, USDA, (301) 504-1624, ekpeabody@ars.usda.gov

Cows will soon have a better chance of getting their needed protein. Scientists with the Agricultural Research Service recently discovered an environmentally friendly way to reduce the protein breakdown that occurs when forage crops like alfalfa are processed into silage, the winter feed of many livestock. Because it's high in protein, alfalfa is an ideal crop for livestock. Unfortunately, when it's processed by storing and fermenting its clippings in silos, up to 85 percent of alfalfa's protein breaks down into nonprotein nitrogen, which can't be used as efficiently by the cows' bodies.Red clover contains large amounts of an enzyme called polyphenol oxidase, or PPO. When red clover is chopped up, its cells release the PPO. When the PPO is exposed to oxygen, it reacts with caffeic acid naturally present in the clover and forms o-quinone molecules. These molecules bind to the enzymes that cause the breakdown of red clover's protein, thereby keeping more protein intact.

Alfalfa has significantly lower levels of PPO. So to take advantage of this PPO-caffeic acid combination to protect alfalfa's protein, Sullivan and ARS plant pathologist Deborah Samac "borrowed" the PPO gene from red clover and inserted it in alfalfa plants. When the altered alfalfa plants were chopped and treated with caffeic acid, they had 15 percent less protein degradation after two weeks than did untreated alfalfa plants.

Caffeic acid is present in high concentrations in a variety of fruits and vegetables, most notably potato skins, a common agricultural waste product. The scientists are working with different potato processing plants to see how easy it would be to extract large amounts of caffeic acid from leftover skins.

Research Indicates Grass-Fed Beef Offers Health Benefits

Grass-fed beef has more beta-carotene, vitamin E and omega-3 fatty acids than beef produced using conventional cattle-feeding strategies, according to a research review conducted by University of California Cooperative Extension and California State University, Chico. Grass-fed cattle live out their lives on the range or pasture eating grass or hay. Their meat is leaner, less tender and contains the higher nutrient levels. It is also a product that can be marketed at a higher price, making grass- feeding a value-added process that can help cattle producers earn more money during difficult economic times. The report concluded that ranchers who produce grass-fed cattle may rightfully claim the product is more healthful than conventionally produced meat. The report says that three ounces of ground beef from cattle fed conventional diets contain about 41 micrograms of beta-carotene and a typical rib eye steak has 36 micrograms. In contrast, meat from cattle fattened predominately on ryegrass has almost doubles the beta-carotene, 87 micrograms in 3.5 ounces of ground beef and 64 micrograms in a steak.