Photos courtesy of AAFC: Soybean responses to Phytophthora sojae. Root rot disease can cause major damage to soybean fields

A new and unusual discovery by Agriculture and Agri-Food Canada (AAFC) represents the first time a pathogen has broken Mendel's Law, a genetic law that states how characteristics are passed on through inheritance. This discovery could impact the control and management of soybean root rot disease, a major problem worldwide. A paper highlighting this discovery recently appeared in the scientific journal Nature Communications.

Soybeans are one of the most important crops in the world's food supply, but they are vulnerable to soybean root rot, a disease caused by Phytophthora sojae. AAFC research scientist Dr. Mark Gijzen is part of a team that discovered a previously unknown way in which the soybean root rot pathogen is able to defeat plant resistance and adapt for survival. With this new information, scientists will alter how they study the pathogen to create better targeted methods of control and management of the disease, in turn helping producers and the soybean industry.

Dr. Gijzen discovered that virulence in P. sojae is passed on, but not through the normal means of inheritance from parent organisms to their offspring described by Mendel's laws. The pathogen actually breaks Mendel's laws and uses something called transgenerational gene silencing to pass on traits that enable it to infect and kill soybean plants.

"This is an extremely unusual phenomenon we've never seen before," says Dr. Gijzen. Working with a team of experts from Oregon State University and Nanjing Agricultural University (China), Dr. Gijzen is researching methods for detecting, monitoring and controlling P. sojae.

"Transgenerational gene silencing is an epigenetic phenomenon, meaning the unit of inheritance is not the DNA sequence of the gene but rather some other self-propagating factor; in this case we believe it to be small RNA molecules. This has big implications that will affect the evolution of this pathogen and how we control it."

In Canada, soybeans are grown on 1.5 million hectares in Ontario, Manitoba, Quebec and Prince Edward Island. Soybean root rot causes widespread damage amounting to annual production losses of $40-50 million in Canada and $1-2 billion worldwide. Agriculture and Agri-Food Canada has made significant contributions to studying the disease since its first appearance in southern Ontario in the 1950s.