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First Report of Gray Mold of Strawberry Caused by Botrytis caroliniana in North Carolina

Gray mold caused by Botrytis spp. is one of the most economically important diseases of cultivated strawberry (Fragaria × ananassa) worldwide. In June 2011, strawberry fruit that was symptomatic of gray mold disease was collected from High Point county in North Carolina. Fruit had brown lesions that enlarged quickly and were covered with green-gray masses of spores followed by a soft rot. To isolate the causal agent, conidia were scraped off the fruit, suspended in 1% Tween 20, spread on water agar amended with 0.1% lactic acid, and emerging colonies were then transferred onto potato dextrose agar (PDA) medium. All but one single-spore colony (designated HP33) were at first colorless and later became gray to brown when the conidiphores and conidia developed on PDA. Isolate HP33 was white to pale gray with short, tufted aerial mycelium, black sclerotia in concentric rings, and did not produce conidia on PDA. Conidia were subhyaline to light brown, smooth, ellipsoid, ovoid or obovoid, and were on average 11.7 × 8.6 μm. The conidiophores were erect, septate, and brown to subhyaline from the base to apex, with swollen basal cell and multiple inflated conidiogenous cells. These morphological features were consistent with Botrytis caroliniana X. P. Li & G. Schnabel sp. nov., a new species isolated recently from blackberry fruit in South Carolina (2). All other single-spore isolates were confirmed to be B. cinerea as described previously (1). To confirm the identity of isolate HP33 to the species level, the necrosis and ethylene-inducing protein 1 (NEP1) was PCR amplified and sequenced by primer pairs NEP1for/NEP1rev as described previously (3). The nucleotide sequence matched the ones published for B. caroliniana (GenBank Accession Nos. JF811593, JF811594, and JF811595). Pathogenicity tests were conducted by inoculating 10 surface-sterilized strawberry fruit with single agar plugs (6 mm in diameter) containing actively growing mycelium; 10 control fruit received agar plugs without mycelium. The inoculated fruit were incubated for 3 days at room temperature in airtight plastic bags and after that developed typical gray mold symptoms. Koch's postulates were fulfilled by the reisolation of B. caroliniana from symptomatic fruit. Control fruit remained healthy. To our knowledge, this is the first report of B. caroliniana on strawberry. It is uncertain whether the new species requires management strategies different from those that control gray mold caused by B. cinerea.

References: (1) D. Fernández-Ortuño et al. Plant Dis. 95:1482, 2011. (2) X. P. Li et al. Mycologia 2012, doi:10.3852/11-218. (3) M. Staats et al. Fungal Genet. Biol. 44:52, 2007.