Soybean School: New test helps find best variety for fighting phythophthera root rot


Researchers at Laval University in Quebec have developed a hydroponic lab test that could allow growers and agronomists to better deploy genetic resistance and tolerance in the fight against phytophthora root rot in soybeans.

There are three main ways to curb phytophthora, explains Geneviève Arsenault-Labrecque, co-founder of AYOS Technologies, a spinoff founded by students at Laval, in this Soybean School episode.

The first tool is seed treatment, but it’s temporary, as it loses its effectiveness as the roots emerge.

The second line of defence in preventing phytophthora is genetic resistance. Seed catalogues and suppliers will often state which Rps (resistance to Phytophthora sojae) genes a variety carries. There are five main Rps genes in commercial soybean varieties (Rps1a, Rps1c, Rps1k, Rps3a and Rps6), but these genes are often ineffective against the predominant pathotypes causing root rot in a field.

“If you have the right genes [in your variety], you will get full protection from planting to harvest, but the problem is that growers do not know which Rps genes to use, because to know which one to use, you need to know which pathotype or races or variant of the disease you have in your field,” she notes.

Using a molecular diagnostic test developed in their lab at Laval, she explains they’re able to identify the race or variant of Phytophthora sojae that’s present in a field.

The third — and increasingly important — line of defence against phytophthora is what’s called “field tolerance,” or more general genetic resistance to many Phytophthora races.

“The plant will get sick, but they will be able to tolerate the presence of the disease, so you will get less symptoms. This is a really good option for growers that are not able to find the right genes, because sometimes you know which genes to use, but you don’t have this in your options from your seed suppliers,” explains Arsenault-Labrecque.

Enter the new hydroponic greenhouse test developed at Laval and commercialized by AYOS, which is seen as a breakthrough in understanding and comparing field tolerance between different soybean varieties.

“What we are offering is we are characterizing the soybean varieties from seed suppliers for the tolerance on Phytophthora root rot using a hydroponic system…It’s appreciated from most agronomists because it offers the possibility to get one rating scale for every seed supplier. And it’s really consistent and it gives really clear results about the tolerance on Phytophthora sojae,” says  Arsenault-Labrecque. (article continues below video)

Geneviève Arsenault-Labrecque explains how a new diagnostic test can help growers choose the best varieties to combat phytophthera in this episode filmed at the 2022 Manitoba Crop Diagnostic School at Carman, Man.:

Field tolerance ratings have traditionally been done in the field, with results only known at the end of a season. AYOS’ new test allows for ratings within a month and a half, she says.

In addition to demand for the test in Quebec and Ontario, Manitoba Agriculture and Manitoba Pulse and Soybean Growers have initiated a project with AYOS to collect ratings on all the varieties in their trials.

“Our hope is that this method of characterization becomes a reference for all seed companies,” says Arsenault-Labrecque. “So when a crop advisor looks for soybean variety across different seed companies, they get the same rating scale, and they can rely on the results that they get about the tolerance on phytophtora root rot.”

Working with a farmer in Ontario last year, she says they saw a 6.7 bushel/acre increase based on choosing a variety with the best-suited genetic resistance, compared with another variety that had the same yield potential, but the wrong genetic resistance.

The molecular test that AYOS is also being deployed to better understand genetic resistance to soybean cyst nematode. Arsenault-Labrecque says they’re also working with Agriculture and Agri-Food Canada on the development of a similar diagnostic tool to identify SCN races.

“We want the growers and crop advisors to be able to exploit resistance sources that already exist — both resistant genes and tolerance — just by selecting the right soybean variety.”


Soybean School: Fighting phytophthora with genetic resistance

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