DNA sequence analysis of herbarium specimens facilitates the revival of Botrytis mali, a postharvest pathogen of apple

Abstract

The fungus Botrytis cinerea has been widely accepted as the species responsible for causing gray mold decay of apple, although a second species causing apple decay, B. mali, was reported in 1931. Botrytis mali was validly published in 1931, nevertheless it has always been considered a doubtful species. To study the relationship of Botrytis isolates causing gray mold on apple, DNA sequence analysis was employed. Twenty-eight Botrytis isolates consisting of 10 species were sampled, including two B. mali herbarium specimens from apple originally deposited in 1932. The DNA sequence analysis of the β-tubulin and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) genes placed the isolates into groupings with defined species boundaries that generally reflected the morphologically based model for Botrytis classification. The B. cinerea isolates from apple and other host plants were placed in a single clade. The B. mali herbarium specimens however always fell well outside that clade. The DNA sequence analysis reported in this study support the initial work by Ruehle (1931) describing the apple pathogen B. mali as a unique species.

• morphology
• phylogenetics
• plant pathogen
• systematics

The authors appreciate the assistance Colleen Harlton, AAFC, Summerland, for her excellent technical support, Scott Redhead, National Mycological Herbarium, AAFC, Ottawa, for nomenclatorial advice, Timothy C. Paulitz, USDA-ARS, Washington State University at Pullman, and Jack D. Rogers, Department of Plant Pathology, Washington State University at Pullman, for searching for specimens, and Erin McCray and colleagues, National Fungus Collections, USDA, Beltsville, for loan of specimens.