A TEAM of Purdue University researchers, led by Jianix Ma and Teresa Hughes, discovered two genes within the soybean genome that are highly resistant to the pathogen that causes Phytophthora root and stem rot while searching for a genetic solution to another soybean problem — Asian soybean rust.
The discovery could be a game changer for the future of soybean breeding programs.
In 1948, Phytophthora root rot was first discovered in Indiana and spread quickly throughout the U.S. and Canada, causing a widespread problem for soybean growers. The disease still remains an ongoing challenge for farmers. Annually, the reduction in soybean yields from root and stem rot costs growers $1-2 billion worldwide.
Phytophthora root and stem rot is caused by Phytophthora sojae, a fungus that survives on plant debris and in the soil indefinitely.
Early heavy rains, cool conditions and poor drainage can provide the optimal environment for the fungus to flourish.
The pathogen produces spores that remain dormant in the soil during the winter months. As the temperature rises, the spores will germinate, travel through water-filled soil pores and infect the soybean plant. Brown lesions, produced from diseased roots, move up the stem, killing the entire soybean plant.
Resistance is the key to controlling the disease. P. sojae-resistant genes exist in soybean germplasm naturally. In the past, other resistant genes have been acknowledged. However, over time, these genes have lost their ability to repel the pathogen. Ma, a soybean geneticist in Purdue's agronomy department, reported that together, the two newly identified genes appear to be stronger.
"These two genes demonstrate resistance to all the predominant isolates of this pathogen found in Indiana and many other isolates that are virulent to previously identified resistance genes," Ma said. "If these two genes are effectively used in Indiana and other Midwest soybean crops, an annual net increase in soybean production would be anticipated."
During three years of study, the Purdue team has developed molecular "markers" to speed up the process of transferring the resistant genes to soybean cultivars.
"There are about 46,000 predicted gene models in what we call the reference soybean genome," Ma said. "These markers allow rapid pyramiding of multiple resistant genes into a single cultivar in order to boost the effectiveness of resistance."
At this point, the longevity and effectiveness of the two resistant genes is unknown.
"We believe these genes are durable, but we don't know enough about them yet to predict how effective they could be and for how long," said Hughes, a U.S. Department of Agriculture plant pathologist and adjunct professor in Purdue's department of botany and plant pathology.
The next step for the research team is to move the work from the greenhouse to the soybean field. After they are tested in field trials, the resistant lines could be available for commercial cultivars.
The Theoretical & Applied Genetics paper, "Molecular Mapping of Two Genes Conferring Resistance to Phytophthora sojae in a Soybean Landrace PI 567139B," is available at http://link.springer.com/content/pdf/10.1007%2Fs00122-013-2127-4.pdf.