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Poster: Biology & Disease Mgmt: Chemical Control


In-vitro azoxystrobin sensitivity of Colletotrichum gloeosporioides isolates from blueberry in north and central Florida
M. VELEZ-CLIMENT (1), P. Harmon (1) (1) University of Florida, U.S.A.

Anthracnose pathogens cause destructive diseases of blueberry fruits, leaves, and stems in Florida. Growers in central Florida have reported a lack of efficacy from QoI fungicides, specifically for anthracnose stem cankers on the southern highbush blueberry variety Flicker. Twenty-two single-spore isolates collected from symptomatic stems, leaves, and berries were identified and tested for sensitivity to QoI fungicides. Percent inhibition (PI) of conidial germination on PDA plates amended with 10µg mL-1 of azoxystrobin demonstrated all isolates from central Florida farms were insensitive to azoxystrobin. Isolates from north Florida farms were sensitive. Internal transcribed spacer region (ITS) sequence comparisons grouped all isolates within the C. gloeosporioides species complex, and the diverse morphology of the colonies and conidia agreed with this placement. These data suggest the fungicide failures reported by growers in central Florida were due to selection of QoI fungicide insensitivity in stem-infecting populations of C. gloeosporioides. Furthermore, insensitive isolates from fruits and leaves indicate that the fungicide azoxystrobin may no longer be a viable management option for ripe rot and anthracnose leaf spot, either. Additional efforts are needed to determine the nature and distribution of the resistance, to develop alternative management options, and to reinforce good resistance management practices for Florida’s blueberry industry.