Good news for soybean growers

WOOSTER, Ohio – 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.

What it means. 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.

The results were the culmination of over 10 years of research.

Resistance. 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.

What if … 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 resistance. 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.”

Plant durability. 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.

Permanent change. “Once those new partial resistant genes are identified, companies will be off to the races in providing new soybean resistant packages. And growers will always have a nice plant package to grow in Ohio,” said Dorrance.

“If seed companies would use partial resistant packages or combine partial resistance with a single gene, then growers should never again see major yield losses to Phytophthora.”