Multiple Alternaria species groups are associated with leaf blotch and fruit spot diseases of apple in Australia

• Published in: Plant pathology Vol. 62; no. 2; pp. 289 - 297
• Main Authors: Harteveld, D. O. C, Akinsanmi, O. A, Drenth, A
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-04-2013; Blackwell; Wiley Subscription Services, Inc
• Subjects: Alternaria; Alternaria allergen a1; apples; Biological and medical sciences; endopolygalacturonase; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; genes; hyphomycetes; leaf blotch; leaves; orchards; pathogens; phylogeny; Phytopathology. Animal pests. Plant and forest protection; sequence analysis; small‐spored Alternaria; sporulation; sporulation patterns; New South Wales; Queensland; Australia; Oceania; Alternaria allergen a1; Plant pathology; Disease; Climacteric; Temperate zone; small-spored Alternaria; Fungi; Pectinolytic enzyme; Sporulation; Fungi Imperfecti; Species; Multiple; Small; Enzyme; Alternaria; Pome fruit; Plant leaf; Polygalacturonase; sporulation patterns; Glycosylases; Apple; Glycosidases; Vegetative apparatus; hyphomycetes; Hydrolases; endopolygalacturonase
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/j.1365-3059.2012.02637.x

Leaf blotch and fruit spot of apple caused by Alternaria species occur in apple orchards in Australia. However, there is no information on the identity of the pathogens and whether one or more Alternaria species cause both diseases in Australia. Using DNA sequencing and morphological and cultural characteristics of 51 isolates obtained from apple leaves and fruit with symptoms in Australia, Alternaria species groups associated with leaf blotch and fruit spot of apples were identified. Sequences of Alternaria allergen a1 and endopolygalacturonase gene regions revealed that multiple Alternaria species groups are associated with both diseases. Phylogenetic analysis of concatenated sequences of the two genes resulted in four clades representing A. arborescens and A. arborescens‐like isolates in clade 1, A. tenuissima/A. mali isolates in clade 2, A. alternata/A. tenuissima intermediate isolates in clade 3 and A. longipes and A. longipes‐like isolates in clade 4. The clades formed using sequence information were supported by colony characteristics and sporulation patterns. The source of the isolates in each clade included both the leaf blotch variant and the fruit spot variant of the disease. Alternaria arborescens‐like isolates were the most prevalent (47%) and occurred in all six states of Australia, while A. alternata/A. tenuissima intermediate isolates (14%) and A. tenuissima/A. mali isolates (6%) occurred mostly in Queensland and New South Wales, respectively. Implications of multiple Alternaria species groups on apples in Australia are discussed.