Soybean School: Progress in the fight against phytophthora root rot

New developments in testing are expected to provide soybean growers with valuable information to fend off yield-robbing root rot caused by the water mould known as Phytophthora sojae.
Beyond crop rotation and drainage, selecting varieties with genetic resistance, through major genes and overall field tolerance, is the best management tool for mitigating phytophthora infection, but new pathotypes that can overcome the common resistance genes continue to emerge.
Fortunately, a new test developed by researchers at Laval University has dramatically reduced the amount of time it takes to determine which pathotypes are present in a soil sample.
In 2023, for the first time, soil samples collected as part of the annual soybean disease survey in Manitoba were sent for analysis to determine which phytophthora pathotypes were present.
84 per cent of the fields in Manitoba that were surveyed in '23 had the potential to infect soybeans with phytophthora, says Laura Schmidt, production advisor with MPSG, in this Soybean School episode.
The research also showed that unfortunately, the resistance genes that are most common in commercial soybean varieties in Manitoba, such as Rps 1C and Rps 1k, are also the most commonly defeated, based on pathotypes found in soil samples. Rps 3a and 6 are not as readily available in commercial varieties, but are more likely to be effective.
"This is a key piece of phytophthora management in terms of knowing what pathotypes are in your soil. You can actually pair that with an effective RPS gene for that major gene resistance, which is complete protection against phytophthora throughout the growing season," she says, following a presentation on phytophthora during the 2024 Manitoba Crop Diagnostic School in Carman, Man.
In addition to better understanding major gene resistance, growers can also look forward to having a clearer picture of partial resistance or field tolerance, says Schmidt. A project led by Dr. Yong Min Kim at AAFC's research sites in Brandon, Man., Morden, Man. and Harrow, Ont. is using a new test to assess partial resistance to help growers make variety decisions.
"We're testing different varieties for their partial resistance just to get an independent measure that farmers might be able to use. Seed companies are reporting some of those measures for their respective varieties, but they're all using different scales, so it's hard to compare between seed companies," says Schmidt. "I think that's really exciting."
Finally, she says there's also work underway on new "tailgate" tests to rapidly determine in the field whether an infection is caused by phytophthora or not.
Given the moisture that many soybean-growing areas have received this year, she says these new developments in understanding phytophthora could be front of mind for growers and agronomists in the coming weeks.
#soybeans #agronomy #farming
Website: www.realagricu...
Find us on our other social media platforms:
X/Twitter: / realagriculture
Instagram: / realagriculture
Facebook: / realagmedia