20 years of SCN bean variety trials

The Iowa State University trials that rate the performance of commercially available soybean varieties for resistance to soybean cyst nematode in Iowa reached a milestone in 2011. “We’ve been doing this testing each year for 20 years now,” says Greg Tylka, an ISU Extension nematologist who oversees the program. “And I didn’t realize it was 20 years until we were finished with the publication reporting the 2011 results.”

Time flies when you’re having fun, and Tylka has been there from the beginning. He and his team of research technicians analyzed the results after harvest at various locations around Iowa this past fall and finished up the “2011 SCN-resistant Soybean Variety Trial” publication in December. The report is available online from ISU and the Iowa Soybean Association. Printed copies have also been distributed.

Key Points

ISU’s soybean variety testing program for cyst nematode marked 20 years in 2011.

Annual SCN-soybean variety trial results are very helpful for soybean growers.

The testing shows differences in SCN control among various soybean varieties.

Farmers use the trials’ results as a source of information in choosing SCN-resistant soybean varieties to plant, as part of their management to control the soybean cyst nematode, a tiny worm that robs soybean yields.

The ISU SCN variety testing program is the largest and most comprehensive of its kind in the nation, and the results are used not just by farmers in Iowa, but by farmers and agronomists in states throughout the Midwest and Northeast. The research is funded by Iowa soybean farmers through a grant from the Iowa Soybean Association.

Tylka is an ISU professor of plant pathology and microbiology, with Extension and research responsibilities in management of plant-parasitic nematodes. Tylka also tests and researches other corn nematodes that can attack corn roots. He’s the “go-to guy” for management recommendations and answering farmers’ and agronomists’ questions about nematodes.

Plant SCN-resistant beans

SCN is one of the most damaging pests of soybeans in Iowa and throughout the Midwest. “The amount of yield loss that occurs is directly related to the SCN egg population densities [numbers] in the soil,” explains Tylka. “The higher the egg number, the greater the yield loss.

So keeping SCN egg population densities from increasing to high levels is needed to maintain profitable soybean production in SCN-infested fields. An effective way to produce high soybean yields and keep SCN egg population densities in check is to grow SCN-resistant soybean varieties.”

Iowa farmers can choose from more than 800 soybean varieties described as resistant to SCN as was recently discussed in ISU Extension’s Integrated Crop Management newsletter. SCN resistance is never 100% effective, but varieties that allow less than 10% SCN reproduction meet the scientific definition of SCN resistance.

Soybean varieties vary greatly in yield and nematode control. “There are differences in nematode control among resistant varieties because there are at least four different genes involved in conferring resistance to SCN in soybeans, and not every SCN-resistant soybean variety has all of the genes in the same combination,” says Tylka.

“Soybean varieties with fewer SCN resistance genes will allow more SCN reproduction than varieties with the full complement of resistance genes. The amount of SCN reproduction that a variety allows is not provided in the description of the variety.”

Iowa State University annually evaluates SCN-resistant soybean varieties at multiple locations throughout Iowa. Each variety is studied in replicated plots to determine how well the variety yields and how well it controls the nematode pest in the soil.

A few widely grown SCN-susceptible soybean varieties are included in each experiment for comparison purposes. The results of the 2011 experiments were finalized in December and are available in ISU Extension publication IPM 52, “Evaluation of Soybean Varieties Resistant to Soybean Cyst Nematode in Iowa — 2011.”

Rating soybean varieties

A new graph style adopted for the 2011 report shows yield and magnitude of SCN reproduction in the same bar graph for various soybean varieties. Almost all of the resistant varieties evaluated in 2011 had SCN resistance from PI 88788. Four varieties for northern Iowa and three for central Iowa had Peking SCN resistance, and one variety with PUSCN14 SCN resistance was evaluated in all three regions of Iowa.

Although many plots are established and intensively studied throughout Iowa each year in the ISU SCN-resistant Soybean Variety Trial Program, Tylka cautions that the data are from a relatively limited number of locations. Also, many other factors can affect soybean yields.

“The results of these annual ISU experiments should be one of several types of information Iowa farmers and agronomists consider when developing an SCN management program for any specific field,” he adds.

Results from all variety trial locations from 1997 through 2011 can be found at www.isuscntrials.info. Also, more information about the biology and management of SCN is at www.soybeancyst.info.

This article published in the February, 2012 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.