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 “We don’t have hard numbers yet, but this pathogen in other
systems can cause up to 20% yield losses,” says Jamann, an
assistant professor in the Department of Crop Sciences at the
University of Illinois and co-author of a new study in the
journal Crop Science. “There’s no effective chemical control.
Fungicides don’t work, as it’s a bacterial disease. That’s why
host resistance is going to be critical, just as it is for
controlling other bacterial diseases of corn, such as Goss’s
wilt and blight.”
The disease-causing bacteria squirm in through open pores –
stomata – on the leaf surface, then set up shop between veins to
form long greyish streaks. Although no one has determined
precisely what’s happening inside the plant, Jamann says the
necrotic lesions are disrupting the photosynthetic capacity of
the leaf. And that hurts yield.
To make matters worse, bacterial leaf streak looks similar to a
fungal disease of corn, gray leaf spot. Farmers may confuse the
two diseases and spray fungicide, which is not only ineffective,
it’s an unnecessary cost.
Currently, there is no chemical control agent for bacterial leaf
streak, and no completely resistant corn hybrids exist. But, in
the Crop Science study, Jamann and her collaborators make a
promising discovery that could lead to resistant lines in the
future.
By inoculating 26 diverse corn lines with the disease and
selecting promising lines for further analysis, they found corn
varieties with moderate resistance and genetic regions
associated with increased levels of resistance.
“Although we didn’t identify any large-effect resistance genes,
the study is the first report of host resistance to bacterial
leaf streak that has ever been published,” Jamann notes.
The team also looked for relationships between resistance to
bacterial leaf streak and three other foliar diseases of maize,
for which host resistance is better understood.
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The hope was that the same genes would also have an
effect for bacterial leaf streak, but the relationships were not
clear-cut.
“We find that the genetic architecture of resistance
is complex, with lots of regions of the genome contributing to
resistance,” Jamann says.
Although the researchers didn’t identify a “smoking gun,” the
information provided in the study should still be useful to breeders
in the process of developing new hybrids with resistance to
bacterial leaf streak. And that’s key.
“Management practices can only go so far in reducing losses due to
this disease. You can’t always control the conditions to avoid
disease spread,” Jamann says. “Ultimately host resistance is going
to be critical.”
The article, “Identification of quantitative trait loci associated
with maize resistance to bacterial leaf streak,” is published in
Crop Science [DOI: 10.2135/cropsci2019.05.0318]. Authors include
Yuting Qiu; Chris M. Kaiser; Clarice Schmidt; Kirk Broders; Alison E
Robertson; and Tiffany M. Jamann. The research was supported by
grants from FFAR, USDA APHIS, and USDA Hatch.
The Department of Crop Sciences is in the College of Agricultural,
Consumer and Environmental Sciences at the University of Illinois.
[Source: Tiffany Jamann News writer:
Lauren Quinn]
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