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POSTERS: Fungicide and antibiotic resistance

Competitiveness of Multifungicide Resistant Botrytis cinerea Isolates Under Field Conditions
Mengjun Hu - University of Maryland. Scott Cosseboom- University of Maryland, Guido Schnabel- Clemson University

Botrytis cinerea isolates with resistance to multiple chemical classes of fungicides pose a great threat to the continuous use of site-specific fungicides. A better understanding of competitiveness of Botrytis isolates with multifungicide resistance will allow us to improve resistance management strategies. In the present study, a mixture of spore suspensions of sensitive B. cinerea isolates (0CCR), isolates with five chemical classes resistances (5CCR), or 7 CCR was artificially inoculated on blackberry plants at 20 to 30% bloom in 2016. Botrytis isolates were recovered from symptomatic or asymptomatic flowers and fruit from each treatment over the course of three years (2016 to 2018). No fungicide was applied during the three experimental years. In 2016, 0CCR, 5CCR and 7CCR isolates were collected from the 0CCR, 5CCR and 7CCR treatments, respectively, but a wide range of phenotypes (i.e. 0, 2, 3, and 4CCR) were also collected from the uninoculated control plants. Multiple CCR phenotypes were observed in each treatment in the following two years. 7CCR isolates were isolated in all of the three experimental years. Sequence analysis of mrr1 gene showed 7CCR isolates isolated in year 3 had the same genotype with those 7CCR isolates used for the inoculation in year 1. These findings indicate that B. cinerea isolates with multifungicide resistance may be as competitive as other phenotypes including isolates sensitive to fungicides in the absence of fungicide selection.