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Morphological, Genetic, and Pathogenic Characterization of Colletotrichum acutatum, the Cause of Anthracnose of Almond in Australia

August 2009 , Volume 99 , Number  8
Pages  985 - 995

Suzanne F. McKay, Stanley Freeman, Dror Minz, Marcel Maymon, Margaret Sedgley, Graham C. Collins, and Eileen S. Scott

First, sixth, and seventh authors: The University of Adelaide, School of Agriculture, Food and Wine, PMB 1 Glen Osmond, South Australia, 5064, Australia; second and fourth authors: Department of Plant Pathology, and third author: Institute for Soil, Water and Environmental Sciences, ARO, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel; and fifth author: The University of New England, Faculty of the Arts and Sciences, Armidale, New South Wales, 2351, Australia.

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Accepted for publication 3 April 2009.

Almond anthracnose was reported for the first time in Australia in 1998 and has since been observed in all of the major almond-growing regions. The organism causing anthracnose was confirmed as Colletotrichum acutatum using taxon-specific polymerase chain reaction (PCR). Three main morphotypes of C. acutatum from almond in Australia were identified (namely, pink, orange, and cream colony color) and the optimum temperature for mycelial growth of representative isolates was 25°C. Australian isolates of C. acutatum were more similar morphologically to the pink subpopulation of C. acutatum from California than to the gray Californian subpopulation and the isolates of Colletotrichum from Israel. Inter-simple-sequence-repeat (ISSR) PCR analysis revealed that the majority of Australian isolates shared an identical banding pattern whereas Australian isolates of C. acutatum from almond were distinct from isolates of the pink and gray subpopulations of C. acutatum from almond in California and of Colletotrichum spp. from almond in Israel. Sequence analysis of the internally transcribed spacer (ITS1-2) ribosomal DNA region of representative isolates differed from the results of ISSR-PCR in that polymorphisms were revealed among isolates, indicating that some genetic variation may be present. Pathogenicity experiments on detached leaves and fruit revealed pathogenic variation among representative isolates of C. acutatum from almond in Australia, California, and Israel; however, all isolates tested caused disease. Distinct subgroups among Australian isolates of C. acutatum from almond were not supported on the basis of morphology, mycelial growth rates, ISSR-PCR, and pathogenicity.

© 2009 The American Phytopathological Society