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Etiology and epidemiology of Alternaria leaf blotch and fruit spot of apple in Australia.
D. O. HARTEVELD (1), O. A. Akinsanmi (1), A. Drenth (1). (1) The University of Queensland, Brisbane, QLD, Australia

Alternaria leaf blotch and fruit spot of apple caused by <i>Alternaria</i>, are important diseases in the Australian apple industry. Control measures are inadequate, there is little information on the epidemiology and the identity of the pathogen(s) is still unknown in Australia. The aims of this study were to determine the identity, diversity and distribution of the pathogen(s) and determine essential features of the disease cycle such as sources of inoculum, overwintering, seasonal dynamics, timing of infection and infection process of <i>Alternaria</i> spp. in Australian apple orchards. DNA sequencing using endopolygalacturonase and <i>Alternaria</i> allergen a 1 gene of 51 Australian isolates from symptomatic leaves and fruit of the six states of Australia identified 5 <i>Alternaria</i> species; <i>A. alternata</i>, <i>A. arborescens</i>, <i>A. tenuissima</i>, <i>A. mali</i> and <i>A. longipes</i>. <i>A. arborescens</i> isolates were the most prevalent and occurred in all the six states of Australia, while <i>A. alternata</i> and <i>A. tenuissima</i> occurred mostly in the regions where the fruit spot disease occurs. The sources and dynamics of <i>Alternaria</i> inoculum, the timing of disease development and climatic influences were investigated. Leaf residue provides the biggest contribution to <i>Alternaria</i> inoculum within the orchard, however conidia were also obtained from twigs during the year, indicating that leaf residue and twigs serve as overwintering sources. Timing of disease expression in the field relates to periods of warm temperatures and high rainfall. Our findings increase our understanding of <i>Alternaria</i> diseases in Australia and will aid in the development of improved control options.<p><p>Keywords: Fungus, Fruits-Nuts, Apple

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