7/27/01

Contacts:
Mark Westgate, Agronomy, (515) 294-9654
Brian Meyer, Agriculture Communications, (515) 294-0706

PEST-RESISTANT SOYBEANS MAY EXCEL AT DRAWING WATER FROM SOIL

AMES, Iowa -- Soybeans that are resistant to a major crop pest may be able to dig deeper to quench their thirst than non-resistant varieties.

That's a finding from research led by Iowa State University's Mark Westgate, who is in the second year of a three-year study to determine how soybean plants respond to water-related stresses, especially when combined with other stresses.

Westgate, a plant physiologist in ISU's agronomy department, works with a team of scientists at ISU and the University of Illinois. During last year's growing season, they studied the growth of soybean varieties that were either resistant or susceptible to soybean cyst nematode (SCN) and brown stem rot (BSR). The varieties were grown in fields known to have past infestations of either SCN or BSR.

"One of our goals was to identify possible water-use differences between resistant and susceptible varieties," said Westgate. "Water is the most important factor influencing plant health, growth and yield. The lack of water underlies many physiological stresses. So if we can suggest management strategies that increase the availability of water during plant development, it may lead to better yields."

Preliminary results showed that SCN-resistant varieties appeared to extract water from the soil differently than the more susceptible varieties.

"The resistant ones seem to draw upon water from deeper in the soil earlier in the growing season," Westgate said. "The roots of susceptible varieties didn't have that downward reach, making them more vulnerable to water stress."

"Late in the season, a little extra water goes a long way," Westgate said. In last year's studies, which included a dry fall, he observed that SCN-susceptible varieties began to drop their leaves earlier than resistant ones. "Was earlier leaf senescence associated with the failure of root development? Did the presence of SCN cysts on the roots accentuate the problem? Those are the kinds of questions we're addressing."

Westgate's findings suggest that resistant varieties may have the water-drawing power to recover from other kinds of field stresses. One clue from last year's work was that the SCN-resistant varieties maintained high yields despite a slowdown in growth when herbicides were applied.

He is continuing to investigate whether the capacity for extracting water from deeper soil layers translates into better tolerance against disease and herbicide stresses for some varieties.

Westgate's work is part of the Yields Project, a multistate research program funded by Iowa and Illinois checkoff dollars through the Soybean Research and Development Council (SRDC). The Yields Project is one of the largest soybean research projects ever undertaken to understand factors that limit soybean yields. The project involves scientists at Iowa State, the University of Illinois, the University of Wisconsin and Southern Illinois University.

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