Prevalence of Botrytis Cryptic Species in Strawberry Nursery Transplants and Strawberry and Blueberry Commercial Fields in the Eastern United States.

Botrytis isolates from strawberry transplants originating from Canada and the northern United States as well as isolates collected from strawberry and blueberry commercial fields in the southeastern United States were investigated for the frequency of Botrytis cinerea, other cryptic Botrytis spp. reported recently, and the transposable elements (TE) using six genetic markers. B. cinerea sensu stricto was predominant (94%) in strawberry and blueberry in all surveyed regions. Botrytis group S, a newly reported clade on strawberry from Germany, was found at low frequencies (6%) in strawberry in the United States and Canada and on blueberry isolates from Florida. Neither B. caroliniana nor B. pseudocinerea were detected in the U.S. or Canadian populations. Transposa isolates containing the TE boty and flipper accounted for 74% of 410 isolates studied herein. Isolates containing boty only or flipper only elements were found at 21 and 2%, respectively. However, boty isolates were predominant in the blueberry population with more than 50%. The TE were found in B. cinerea and Botrytis group S at similar frequencies, except that flipper was more frequent (10.7%) in Botrytis group S, compared with 1.6% in B. cinerea. The sensitivity of 256 Botrytis isolates from the different genetic groups described above was evaluated to seven fungicides registered to control gray mold in commercial fields. Results indicate that B. cinerea and transposa isolates have higher resistance frequencies to almost all fungicides tested compared with the other Botrytis genotypes or species, whereas the TE flipper may be related to resistance to fludioxonil. Similarities observed between nursery and commercial field populations and their impact on gray mold development and management are discussed.