Fitness, competitive ability, and mutation stability of isolates of colletotrichum acutatum from strawberry resistant to Qol fungicides

Abstract

Quin one-outside inhibitor (Qol) fungicides arc used to manage anthrac- nosc of strawberry, caused by CoUetotriduon acutatum. However, selection for resistance to Qol fungicides was first reported in 2013 in Florida and. subsequently, in strawberry nurseries and production areas across the United States and Canada C. acuiaium rcsstancc to Qols Ls associated with the GI43A point mutation in the cytochrome b gene. This mutation is known to be associated with field resistance even at high rates of Qol. In this study, we investigated the relative fitness and competitive ability of Qol-resistant and -sensitive C. acutatum Isolates. A fitness comparison did not indicate any difference between resistant and sensitive isolates in aggressiveness, spore production, and mycelial growth at different temperatures. Additionally, in the abscncc of selection pressure, rcsstant and sensitive Isolates were equally competitive. Cultivation of Qol-rcsistant and Qol-senstive Isolates for four culture cycles in vitro in the abscncc of azoxystrobin showed that Qol resistance was stable. The observed lack of fitness penalties and stability of the GI43A mutation in Qol-rcsistant C. acutaium populations suggest that the interruption and further rcintroduction of Qol fungicides might not be an option for strawberry nurseries and fruit production areas. Further investigation of alternative chcmical and nonchcmical C. acutatum control practices, in addition to the integration of multisitc fungicides, is needed to reduce the occurrcncc and distribution of Qol-rcsistant populations in strawberry fields.