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Fitness, Competitive Ability and Mutation Stability of Strawberry Colletotrichum acutatum Isolates Resistant to Quinone-outside Inhibitor Fungicides
Bruna Forcelini: University of Florida; Natalia Peres: Gulf Coast Research and Education Center; University of Florida; Carolina Rebello: Universidade Estadual Paulista
<div>Quinone-outside Inhibitor (QoI) fungicides, are used to manage anthracnose of strawberry, caused by <i>Colletotrichum acutatum</i>. However, selection for <i>C. acutatum</i> resistance to QoI fungicides was first reported in 2013 in Florida, and subsequently in strawberry nurseries and production areas across the USA and Canada. <i>C. acutatum</i> resistance is due to the G143A point mutation in the cytochrome <i>b</i> gene. This mutation is known to cause complete resistance even at high rates of QoIs. In this study, we investigated the relative fitness and competitive ability of QoI-resistant and sensitive <i>C. acutatum</i> isolates. A fitness comparison did not indicate any difference between resistant and sensitive isolates in mycelial growth at different temperatures or on hypertonic media. However, when different ratios of resistant and sensitive isolates were inoculated on detached strawberry fruit, production of conidia by the resistant isolates increased in relation to sensitive isolates. Cultivation of QoI-resistant and QoI-sensitive isolates for four culture cycles <i>in vitro</i> in the absence of azoxystrobin showed that QoI resistance was stable. The observed competitive advantage and stability of the G143A mutation in QoI-resistant <i>C. acutatum</i> populations suggest that the interruption and further reintroduction of QoI fungicides might not be an option for strawberry nurseries and fruit production areas.</div>

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