Stemphylium blight, caused by the fungal pathogen Stemphylium botryosum, is a lentil disease that has only been identified as a problem in recent years. But according to Sabine Banniza, a researcher at the University of Saskatchewan, this may be due to misdiagnosis in the past.
“There isn’t really very solid data out there, partly because lentil surveys aren’t done every year, and partly because not everybody involved in the industry finds it easy to recognize stemphylium blight. Symptoms look similar to other, more well-known, lentil pathogens,” she explains. “This is likely why it hasn’t received much attention — because it has been misdiagnosed.”
Banniza and her team are embarking on the fourth year of a five-year study of stemphylium blight in lentils. The study began, in part, because commercial seed testing labs began frequently identifying the pathogen in seed samples.
According to Faye Dokken-Bouchard, a provincial plant disease specialist in Saskatchewan, stemphylium blight has been identified as a problem in the province, but infection isn’t consistent year to year. “In 2010, the disease was observed in over 80 per cent of the lentil crops surveyed in Saskatchewan, but the levels remained around 35 per cent in 2011, 2012, and 2013,” she says, citing data from small-scale surveys conducted by the provincial government.
In lentils, the symptoms of stemphylium blight appear very similar to those of sclerotinia and botrytis. Dokken-Bouchard says that stemphylium blight initially appears as small, light beige lesions on leaves and leaflets, both above and under the canopy.
“Prolonged moist periods promote further infections and give the upper canopy a grey-brown appearance,” she explains. “As is common in other lentil diseases, infected leaflets fall to the ground, serving as a source of spores for future infections of a wide range of plants.”
Unlike sclerotinia, no white fluffy mould or black sclerotia are visible to the naked eye, says Dokken-Bouchard, and unlike botrytis, no grey fuzzy mould is visible under a magnifying glass or microscope.
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Banniza explains that stemphylium blight differs in another way from other common lentil diseases. As opposed to diseases such as anthracnose or ascochyta blight, which spread in wet conditions when spores are splashed, the stemphylium blight pathogen has airborne spores. This means spores can spread on windy days even in dry conditions, and affect not just lentil but other crops as well.
However, moisture is still necessary for the disease to flourish.
“Moisture is a big aspect of stemphylium’s epidemiology, for infection but not for the spread of the disease,” explains Banniza. “Because of that, we see this disease more when the canopy has developed, because that’s when the plants retain moisture for longer periods, compared to seedlings, which dry up relatively quickly even after rain.”
It isn’t fully clear yet how much stemphylium blight impacts lentil yields. Anecdotal evidence from farmers suggests that the disease can have a significant impact on yield, but this has yet to be confirmed with research data.
Banniza and her team are midway into field tests investigating the point at which stemphylium blight causes yield loss, but because the fungus is an airborne pathogen it’s difficult to do that research — for example, knowing when to time the infection can be tricky.
Initial findings suggest that the disease may impact yield most when infection occurs at early flowering. If the infection takes root toward harvest, however, it may potentially serve as a natural desiccant, says Banniza.
However, if the spores spread early in the season, growers may have a problem on their hands.
“We’ve done one year of field tests, so this is very preliminary, but it looks like early flowering is a critical point,” says Banniza. “So if you get infection in early to mid-flowering you will see a direct impact on yield.”
However, infection can also cause seed staining, so even if there is no reduction in the quantity of seeds, seed staining can impact growers’ return if their crop is downgraded.
And seed staining could result from infection even after early to mid-flowering. “That may mean that even at a somewhat later stage, the fungus can cause economic damage,” says Banniza.
She says that it’s too soon to make recommendations for stemphylium blight management, but concerned growers can employ the same management strategies they’d use for related diseases. “The positive aspect of this is that the fungicides used for ascochyta blight or anthracnose are also effective against stemphylium blight, so it’s a question of ensuring the appropriate timing,” she says.
While Banniza emphasizes that the project is still in its early stages, answers are not far out of reach. “Hopefully by next year we’ll have a better idea of what critical points are in the lentil crop where you want to prevent infection by this pathogen to prevent yield loss,” she says.