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The detection and characterization of QoI-resistant pathogens causing ascochyta blight of pulse crops in Montana
Ayodeji Owati: Montana State University
<div>Ascochyta blight (AB) of pulse crops (chickpea, field pea, and lentils) causes yield loss in Montana, where 1.2 million acres was planted to pulses in 2016. Pyraclostrobin, a Quinone outside Inhibitor (QoI) fungicide is used widely for the management of AB in pulse crops. However, a mutation in the <i>cytochrome b</i> gene has been reported to confer resistance. To evaluate QoI resistance, a total of 1000 <i>Ascochyta</i> isolates were screened. Out of these, 10% from chickpea, 81% were from dry peas, and 9% from lentil seed lots (chickpea = 17, pea = 131, and lentil = 21) from 23 counties in Montana. Analysis of cDNA and protein sequences of isolates indicated resistant isolates contained the G143Amutation in the <i>cytochrome b</i> gene, which commonly confers complete resistance to all QoI fungicides. A multiplex TaqMan assay was developed to discriminate QoI-resistant and sensitive isolates. Using this assay, QoI fungicide-resistant isolates of<i> Didymella rabiei </i>were detected in Daniels, McCone, and Valley Counties MT, from seed produced in 2015 and 2016. In vivo greenhouse studies indicated that isolates with the G143A mutation<i> </i>caused significantly higher amounts of disease than sensitive isolates on pyraclostrobin-treated chickpea plants (p-value = 0.001). These results imply that AB control may be inadequate at locations where resistant isolates were found, and resistant isolates may be spread via seed. <p> </div>

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