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Canker and wood rot pathogens associated with young apple trees and propagation material in South Africa

Lizel Mostert: Stellenbosch University

<div>Canker and wood rot pathogens can cause dieback and decline of young apple trees. This study assessed the occurrence of canker and wood rot pathogens in nursery apple trees and propagation material. Isolations were made from discoloured vascular tissue of certified nursery apple trees collected from four nurseries as well as scion and rootstock mother plant material. Possible fungal pathogens were identified by sequencing relevant genes and phylogenetic analyses. Similar canker and wood rot fungi were isolated from nursery apple trees and from the propagation material. Fourty-five fungal species associated with canker or wood rot were identified with <em>Didymosphaeria rubi-ulmifolii</em> s.l. the dominant species in certified nursery apple trees. Other canker and wood rot pathogens isolated belonged to the Basidiomycetes, Botryosphaeriaceae and Diatrypaceae. It also included species of <em>Cadophora</em>, <em>Coniochaeta</em>, <em>Cytospora</em>,<em> Diaporthe</em>,<em> Didymella</em>, <em>Didymosphaeria</em> and <em>Phaeoacremonium</em>. Sixty-five percent of certified nursery apple trees were infected with canker and wood rot pathogens. Two-year-old branches of 14-year-old Golden Delicious trees were inoculated with 39 species to evaluate pathogenicity. All the species caused lesions that were significantly longer than the control 5 months after inoculation. This study confirmed the presence of canker and wood rot pathogens in apple propagation material as well as certified nursery apple trees.</div>