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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Commodity Protection and Quality Research » Research » Publications at this Location » Publication #305903
Title: First report of Botrytis pseudocinerea causing gray mold on blueberry in North America

Author
item SAITO, S - Kearney Agricultural Center
item MICHAILIDES, T - Kearney Agricultural Center
item Xiao, Chang-Lin

Submitted to: Plant Disease
Publication Type: Research Notes
Publication Acceptance Date: 8/27/2014
Publication Date: 12/1/2014
Citation: Saito, S., Michailides, T.J., Xiao, C. 2014. First report of Botrytis pseudocinerea causing gray mold on blueberry in North America. Plant Disease. 98:1743.

Interpretive Summary: Gray mold, caused by the fungus Botrytis cinerea, is a major postharvest disease of blueberries grown in the Central Valley of California. B. cinerea has been shown to consist of two sibling species, referred to Group I and Group II, and Group I has recently been described as a new species B. pseudocinerea. During 2012-2013, 526 isolates of Botrytis spp. were obtained from decayed blueberry fruit and were identified by both DNA fingerprinting and morphological characteristics. Four isolates were identified as B. pseudocinerea. In laboratory tests, all four isolates were able to cause rot on blueberry fruit. It appeared that this species was present at very low frequency (0.76%). Previously, B. pseudocinerea had been reported in French, German, and New Zealand vineyards. To our knowledge, this is the first report of B. pseudocinerea causing gray mold in blueberry in California and the first report of the presence of this species in North America.

Technical Abstract: Botrytis cinerea has been shown to consist of two sibling species, referred to Group I and Group II, and the two groups can be differentiated by a PCR-RFLP on the Bc-hch gene (vegetative incompatibility locus). Group I has recently been described as a new species B. pseudocinerea. Gray mold caused by B. cinerea is a major postharvest disease of blueberries grown in the Central Valley of California. During 2012-2013, 526 isolates of Botrytis spp. were obtained from decayed blueberry fruit and single-spore cultured. Genomic DNA was extracted and the PCR-RFLP on Bc-hch gene was performed for all isolates. Four isolates showed the distinctive restriction band patterns identical to that of “Group I”. The identity of the four isolates was further confirmed by sequencing four genes: internal transcribed spacer region, partial glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60), and DNA-dependent RNA polymerase subunit II (RPBII). BLAST analysis showed the sequences of the four isolates had 99.8 to 100% similarity to those of B. pseudocinerea. On potato dextrose agar, colony appeared gray; radial mycelial growth rate was 26 mm/day at 19°C in the dark. Conidiophores were simple and erect, and conidia were borne in grapelike clusters, one celled, hyaline, elliptical to ovoid, 15.7 to 6.5 × 9.8 to 5.6 µm (average of 10.1 × 7.4 µm). To test pathogenicity, freshly harvested organic blueberry fruit were surfaced disinfected with 0.5% sodium hypochlorite for 2 min, rinsed with sterile water, wounded, and inoculated by placing 1 µl of a conidial suspension (1.0 × 105 spore/ml) from each isolate into the wound with a pipette. Inoculated fruit were incubated at 20°C for 5 days in the dark. All inoculated fruit developed rot, and no decay was observed on the noninoculated controls. All four isolates were pathogenic, and the fungus was re-isolated from decayed fruit. B. pseudocinerea isolates are known to be naturally insensitive to fenhexamid. Sensitivity to fenhexamid was examined in vitro, and the values of effective concentrations of fenhexamid for 50% growth reduction relative to control for the four isolates ranged from 7.7 to 9.9 µg/ml and were considered resistant to fenhexamid. Based on the morphological, physiological and genetic characteristics, the four blueberry isolates were identified as B. pseudocinerea. It appeared that this species was present at very low frequency (0.76%). Previously, B. pseudocinerea has been reported in French, German, and New Zealand vineyards. To our knowledge, this is the first report of B. pseudocinerea causing gray mold in blueberry in California and the first report of the presence of this species in North America.