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Poster: Biology & Disease Mgmt: Chemical Control


Baseline sensitivity of Phyllosticta citricarpa isolates from Florida to succinate dehydrogenase inhibitor fungicides in vitro study
K. NICOLETTA (1), M. Dewdney (1) (1) University of Florida, Citrus Research and Education Center, U.S.A.

In 2010, Citrus Black Spot (CBS), caused by Phyllosticta citricarpa, was first found in Florida. CBS has a negative impact on fresh market fruit and yield production causing fruit lesions and premature fruit drop. This study assessed 116 monoconidial P. citricarpa isolates from ‘Valencia’ and ‘Hamlin’ with 39 isolates from Collier, 76 from Hendry and 1 from Polk Counties. Isolate sensitivity to the succinate dehydrogenase inhibitor (SDHI) fungicides: boscalid (0, 0.01, 0.1, 1, 5, 10 and 25 µg/ml), fluxapyroxad (0, 0.001, 0.01, 0.05, 0.1, 1 and 5 µg/ml), and fluopyram (0, 0.001, 0.01, 0.1, 0.5, 1 and 5 µg/ml) was evaluated by mycelial growth inhibition assays. The mean EC50 values for boscalid and fluxapyroxad were 0.179 and 0.026 µg/ml, respectively. These EC50 values were significantly different for each fungicide (P <0.001). It is expected the EC50 value of fluopyram will fall between boscalid and fluxapyroxad’s values. In the baseline assay all the isolates tested are sensitive to SDHI fungicides, therefore we expect no mutations in molecular analyses. Developing the baseline sensitivity of P. citricarpa to SDHI fungicides allow for resistance monitoring. In previous studies, P. citricarpa isolates were found to be sensitive to both quinone outside inhibitor (QoI) fungicides and demethylation inhibitor (DMI) fungicides. Thus, SDHI fungicides could potentially be used as rotational sprays with QoI and DMI fungicides to reduce the risk of resistance developing.