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Fungal trunk disease pathogens in South-African olive nurseries

Meagan Vermeulen: Stellenbosch University

<div>The olive industry has been identified as a high growth sector in the South African National Development Plan and therefore of significant importance to the economy. Several trunk disease pathogens were recently associated with diseased olive trees in South Africa. Little is known about the biology of these pathogens and no specific management strategies are in place. The aim of this study was to investigate the status of trunk pathogens in nurseries. Isolations were made from asymptomatic cuttings from mother blocks (stage 1), rooted cuttings (stage 2) and 1-2-year-old trees (stage 3) of eight cultivars in two nurseries. Known olive trunk pathogens of Nectriaceae, Diaporthaceae, Botrysphaeriaceae, Togniniaceae, Phaeomoniellaceae and Pleurostomataceae were recovered. Stage 3 showed the highest incidence, <em>Pleurostoma richardsiae</em> being the most frequently isolated pathogen occurring in 82% and 37% of the trees in the two nurseries, respectively. <em>Phaeoacremonium parasiticum</em> was present in 29% of the trees from one nursery (stage 3). <em>Neofusicoccum australe</em> was detected in stage 1. The remaining pathogens occurred in 10% or less of the material. These results indicate that propagation material from mother blocks harbour low levels of trunk disease pathogens, but that additional infections occur during the nursery process. Management strategies should focus on the prevention and elimination of infections in mother blocks, as well as during the propagation process.</div>