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ARS Home » Southeast Area » Stoneville, Mississippi » Crop Genetics Research » Research » Publications at this Location » Publication #326582
Title: Competition studies of QoI resistant and sensitive Cercospora sojina isolates the causal agent of frogeye leaf spot

Author
item LIN, BINBIN - University Of Tennessee
item KELLY, HEATHER - University Of Tennessee
item Mengistu, Alemu

Submitted to: Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/15/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Frogeye leaf spot (FLS), caused by Cercospora sojina, is a yearly foliar disease in Tennessee and causes substantial economic losses if not properly managed. Quinone outside inhibitor (QoI) fungicides are often used to manage FLS, but C. sojina isolates have developed resistance to this class of fungicides. Since the majority of soybean fields contain both QoI resistant and sensitive isolates, a better understanding of similarities and differences between such isolates in their biology and aggressiveness in causing FLS symptoms is needed. A greenhouse study was conducted at six different spore ratios of QoI resistant and sensitive isolates: 1:0, 9:1, 1:1, 1:9, 1:99, and 0:1. When the plants reached V4 growth stage, three treatments—no fungicide (water control), Quadris (azoxystrobin), and Quadris-Top (azoxystrobin plus difenoconazole) were applied to three replications, each replication consisted of four soybean plants (Blackhawk cultivar). Results of the greenhouse studies indicate that: 1) Disease severity increased as the proportion of QoI-resistance in the inoculum increased, indicating that QoI-resistant isolates are more aggressive; 2) Quadris fungicide only inhibited FLS caused by QoI sensitive isolates and when the proportion of QoI resistance was less than or equal to 10%; 3) Quadris-Top fungicide provided more effective control of FLS, not only by reducing symptoms but also by delaying disease development. This work will contribute to understanding differences in QoI resistant and sensitive C. sojina isolates and identifying any differences in effective control measures for FLS.