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Breakthrough discovery promises resistance against soybean disease

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Media Relations
Agriculture and Agri-Food Canada

Stem and root rot caused by the fungus-like disease Phytophthora sojae (P. sojae) causes approximately $50 million of soybean yield loss in Canada every year. Globally, the losses are between $1 and $2 billion annually. However, a promising new discovery at Agriculture and Agri-Food Canada (AAFC) may significantly reduce these losses and help farmers increase their yields and profits.

In this landmark study, Dr. Sangeeta Dhaubhadel isolated 11 genes in soybeans which function in a critical step in the fight against this devastating disease. One of these genes – GmCHR2A – will be key to breeding new disease-resistant varieties of soybeans.

Until now, farmers have relied on traditional strategies to try to reduce P. sojae infection such as treating their soil with fungicide or calcium, or improving soil drainage and tillage. However these methods have been ineffective and have led to the disease being able to resist the treatment and continue to attack the plants.

Dr. Dhaubhadel’s study is the largest and most comprehensive of its kind in soybean research. It found a naturally occurring trait in soybean that improves resistance – the rapid, increased production of isoflavonoid glyceollins. Chalcone reductase (CHR) is the key enzyme which leads to the production of these glyceollins, and their rapid, increased production is linked to strong partial resistance to P. sojae, a very durable and broad-spectrum type of resistance (lasts for a long time and is effective against many types of dieases).

"This is the first robust study on identifying CHR genes in soybean which are key to creating varieties resistant to P. sojae. A previous study identified only 2 CHR genes. This research is good news for soybean farmers as they can expect to have soybean cultivars that are more resistant to P. sojae."

- Dr. Sangeeta Dhaubhadel, Research Scientist, Agriculture and Agri-Food Canada

Up until now, very little was known about CHR genes. As P. sojae is a soil borne disease, Dr. Dhaubhadel knew that when P. sojae infection occurred, the resistance genes had to be expressed in the roots. She infected soybean stems with P. sojae to see if any CHR genes were activated or not. Then she analyzed existing soybean literature to see if there were any QTL markers (quantitative trait loci) linked to P. sojae resistance. QTLs are genomic regions that contain multiple genes. A total of 77 QTLs were found to be linked with resistance, and in these areas, one out of 11 CHR genes was discovered to be the most critical in the search for resistance – the GmCHR2A gene.

As an added bonus, this gene may also be effective in the fight against other fungal or bacterial diseases, and possibly even initiate a defense response to insects like the soybean aphid.

The next step? Dr. Dhaubhadel is working with Dr. Istvan Rajcan (University of Guelph, Oilseed Cluster) on the search for additional genes and on creating a gene-specific marker so soybean breeders can create new P. sojae-resistant varieties quickly.

Now grown in Alberta, Manitoba, Saskatchewan, Ontario, Quebec and the Maritimes, soybeans have truly become a nationally important crop used for food, feed and industrial purposes with an export value of $2.7 billion.

Key Discoveries (Benefits)

Photo gallery

Healthy green soybean plant beside shrivelled up, brown soybean plant with stem and root rot disease
Healthy soybean plant and plant with stem and root rot disease.
Dr. Sangeeta Dhaubhadel at work in her lab
Dr. Dhaubhadel in lab.
Yellow squiggly lines showing the close-up accumulation of GmCHR2A genes in leaf cells
Accumulation of GmCHR2A leaf cells.

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