Chickpea diseases becoming more resistant: researchers

In the second half of last year’s growing season, Sabine Banniza’s phone began ringing more often than normal.

Banniza is the Saskatchewan Ministry of Agriculture Strategic Research Program Chair in Pulse Crop Pathology, and she’s where agrologists and growers turn when they can’t identify a pulse disease.

In this instance, a disease was sweeping through the chickpea crop in southwestern Saskatchewan that seemed to affect CDC Orion more than other varieties. It wasn’t aphanomyces.

Banniza and her team sat down to try and figure it out.

“The environment was quite challenging last year. We had the driest spring in decades and then wet conditions, dry conditions, wet conditions, so it wasn’t easy for plants,” Banniza said.

“We know that in the chickpea with ascochyta rabiei, there’s a history of fungicide insensitivity, and we were thinking that’s part of the problem. As well, maybe some other stresses, herbicides maybe. Some of the growers thought it may be worse on some fields sprayed with one herbicide rather than others. Maybe there are some virus we haven’t identified, nematodes, who knows.”

The team got to work testing samples Sherrilyn Phelps, SaskPulse agronomy manager, collected in southern Saskatchewan.

Banniza said root rots in chickpea have been increasing and there were multiple suspects that may be contributing to the issue, including fusarium, verticillium, phytophthora, and nematodes.

“There were five samples with root rot, so a very limited number. We found fusarium and we found one sample with phytophthora,” Banniza said.

However, she said the sample size was small and that it likely doesn’t represent the affected areas well, and that more work needs to be done.

“The other issue was, all of these plants very clearly had ascochyta blight caused by ascochyta rabiei. This is the sort of disease that seems to represent a very fast forward movie of what can go wrong with disease. Ascochyta rabiei is the most aggressive foliar disease I reckon we have on the Prairies. It can lead to crop loss very quickly,” Banniza said.

She reminded the crowd what happened to Sanford, one of the first large kabuli chickpea varieties grown when chickpea production became established on the Prairies.

“It was introduced as a variety with good partial resistance to ascochyta rabiei. It was a very attractive large kabuli where you could make a lot of money in the market, so growers loved it,” Banniza said.

But then Sanford crashed partially because the ascochyta rabiei population quickly shifted to a highly aggressive pathotype in the early 2000s.

“Two to three years later, the whole population (of ascochyta rabiei) had shifted to high aggressiveness, and what that means in the field is basically you are experiencing resistance breakdown,” Banniza said.

“My message is this can happen very quickly and varieties that are resistant one year, two or three years later they can be susceptible. That’s probably what we’re seeing.”

She said a second issue is fungicide insensitivity of ascochyta rabiei to strobilurin, a widely used product that is currently the most effective fungicide on ascochyta rabiei.

Banniza said in 2018 when Michelle Hubbard from Agriculture Canada found fields where she identified ascochyta rabiei, she also identified strobilurin resistance in these pathogens.

In 2019, Hubbard looked at more fields and found CDC Orion is more susceptible to ascochyta rabiei compared to other varieties, which suggests the chickpea’s resistance is breaking down.

She also confirmed strobilurin resistance in the ascochyta rabiei population.

“We know it’s most widely ascochyta rabiei that has a long history of this (fungicide resistance) happening,” Banniza said.

She said Ag Canada’s Swift Current operations is monitoring of how the ascochyta rabiei population is changing.

There aren’t any laboratories where growers can send samples to test for ascochyta rabiei that’s strobilurin resistant, but there are some companies such as BASF that may do some testing.

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