Fungicide resistance in populations of Colletotrichum musae from Brazil and evidence of fitness costs for QoI resistant isolates

Abstract

Abstract Anthracnose, induced by Colletotrichum musae, stands as the paramount postharvest ailment affecting bananas. This study sought to assess Brazilian C. musae populations concerning three fungicides Inhibitors External Quinone (QoIs) fungicides, specifically azoxystrobin, pyraclostrobin, and trifloxystrobin, while concurrently exploring the underlying mechanisms associated with resistance. Sensitivity assays were conducted both in vitro and in vivo. A positive and substantial correlation was observed between azoxystrobin and trifloxystrobin, while no correlation was evident between these fungicides and pyraclostrobin. The estimated effective concentration of the fungicide able to inhibit mycelial growth by 50% (EC50) was used to select isolates considered as sensitive (S) and resistant (R), respectively. Despite the resistance results observed in vitro, all fungicides examined demonstrated efficacy against both S and R isolates of C. musae when employed in the treatment of detached banana fruits. Resistance stability was affirmed following ten consecutive transfers in vitro in the absence of fungicidal exposure. In general, the biological fitness of R isolates was lower than that of S isolates, except for isolates resistant to pyraclostrobin, whose sporulation was significantly higher than that of S isolates. The studies on competition substantiate the anticipated fitness outcomes. This study enables a more profound comprehension of the sensitivity to QoIs fungicides and the fitness of C. musae isolates originating from Brazil.