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The biological control of Fusarium wilt of sweet potato using non-pathogenic Fusarium oxysporum and Trichoderma species

Rene Sutherland: Agricultural Research Council

<div>Sweet potato is the 7<sup>th</sup> most important crop globally, and the 2<sup>nd</sup> most important root crop in South Africa. It is produced by small scale farmers, emerging farmers and some commercial farmers in South Africa. Over the years, sweet potato production has declined as a result of Fusarium wilt of sweet potato. Fusarium wilt of sweet potato is caused by <em>Fusarium oxysporum</em> f. sp. <em>batatas </em>(<em>Fob</em>), a fungal soil-borne pathogen. The disease causes symptoms such as wilting, necrosis, internal stem discoloration and leaf yellowing. Control measures are limited and ineffective against Fusarium wilt of sweet potatoes, which has led to the search for an inexpensive and effective control measure. This has intensified the need to focus research on biological control. Roots and soil samples were collected from healthy sweet potato plants in field trials and <em>Fusarium</em> and <em>Trichoderma</em> spp endophytes were isolated. An <em>in vitro</em> dual assay was conducted to screen the antagonistic ability of <em>Fusarium</em> and <em>Trichoderma</em> isolates against <em>Fob</em>. <em>Trichoderma</em> isolates showed antagonistic ability through competition and parasitizing of <em>Fob</em>, while <em>Fusarium</em> isolates only showed competitive ability, with an inhibitory percentage up to 50% for <em>Trichoderma</em> and 30% for <em>Fusarium</em> spp. Inoculation <em>in vivo</em> showed that <em>Trichoderma</em> and <em>Fusarium</em> suppress the disease under greenhouse conditions. According to these observations, both species can be combined and used as bio-control agents as they provide different antagonist modes of action. Potentially, as a result of the study, farmers may be able to manage the disease, optimize their production, and consequently contribute to food security and income generation.</div>