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ISHS Acta Horticulturae 1299: XXX International Horticultural Congress IHC2018: VII International Symposium on Tropical and Subtropical Fruits, Avocado, II International Symposium on Jackfruit and Other Moraceae and II International Symposium on Date Palm

Distribution, detection and management strategies for avocado sunblotch disease (ASBD) in South Africa

Authors:   Z.R. Zwane, A.E.C. Jooste
Keywords:   Avocado sunblotch viroid (ASBVd), distribution, detection, avocado sunblotch disease, sampling strategy
DOI:   10.17660/ActaHortic.2020.1299.58
Avocado sunblotch disease, caused by Avocado sunblotch viroid (ASBVd), is one of the important diseases of avocado that affects yield and quality worldwide. Typical symptoms are found on leaves, fruit and bark of the tree; however, some trees do not display any visible symptoms and are referred to as symptomless carrier trees. The most important control measure for sunblotch disease is careful selection of pathogen-free bud wood and seed that are used for propagation, which are identified by indexing. In this study, the distribution of ASBVd in a single infected tree was studied, molecular variation of ASBVd in infected plants was examined and field surveys were conducted on commercial farms to determine the occurrence of ASBVd. A total of 30 commercial farms and 4 nurseries were visited and 316 trees were sampled randomly from these sites and tested for the presence of ASBVd. In this survey, 11.2% of the trees sampled, tested positive for ASBVd. Uneven distribution of ASBVd within a single plant was detected, between different tree branches and in fruits. The uneven distribution within a plant highlights the importance of proper sampling strategies for ASBVd indexing. Symptomless carrier trees are currently the main concern for the avocado industry and precise sampling strategies and detection systems need to be in place to reduce the spread of ASBVd in avocado orchards.

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