Quinone outside inhibitor-resistant Colletotrichum nymphaeae isolates from strawberry lack mutations in cytb gene
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Quinone outside inhibitor-resistant Colletotrichum nymphaeae isolates from strawberry lack mutations in cytb gene Amanda Chechi 1 & Melanie L. Lewis Ivey 2 & Rachel R. Kaufman 2 & Karen P. Bryson 1 & Guido Schnabel 1 Received: 23 October 2019 / Accepted: 24 April 2020 # Società Italiana di Patologia Vegetale (S.I.Pa.V.) 2020
Abstract Anthracnose fruit rot is one of the main diseases affecting strawberries especially in warm and humid climates. In commercial settings, producers are relying on fungicides to control the disease. One of the most potent chemical classes of fungicides for anthracnose control are the quinone outside inhibitors (QoIs), but resistance in field isolates due to a point mutation in the target gene cytb has recently been reported in multiple states of the USA. During a routine screening, two Colletotrichum nymphaeae isolates (OH_S1 and OH_S2) obtained from strawberry plants of a commercial field in Marietta-Ohio were found to be resistant to QoI fungicide azoxystrobin. The EC50 values determined in poison agar tests were greater than 100 μg/L. Both isolates were not controlled on detached strawberry fruit treated with label rates of Abound fungicide (a.i. azoxystrobin) and revealed disease severity of 86% and 96% on detached fruit. A baseline isolate (Cn_ebel2) of the same species revealed an EC50 value of 1.2 μg/L and no disease developed on Abound-treated fruit. In contrast to other reports, sequencing of the cytb gene from all three isolates used in this study revealed no amino acid changes in cytb, indicating the existence of a different and still unknown resistance mechanism. Keywords Anthracnose fruit rot . Fragaria x ananassa . Fungicide resistance . Strobilurins . Azoxystrobin . Colletotrichum acutatum . Colletotrichum nymphaeae
Anthracnose fruit rot caused by Colletotrichum acutatum species complex is the major disease affecting strawberry (Fragaria × ananassa) fruit but can also affect other parts of the plant including roots, crowns, and petioles. Recently it was established that Colletotrichum nymphaeae, a member of this complex, has been the primary species causing fruit rot in the USA (Wang et al. 2018). The sources of inoculum causing outbreaks can derive from alternate hosts such as forest trees and weeds but are most often traced back to transplants supplied by nurseries (Freeman et al. 2001a, b; Lu et al. 2004; Peres et al. 2005). The pathogen can enter the field in form of latent infections or in form of conidia residing on the surface on any of the strawberry plant parts (Peres et al. 2005).
* Guido Schnabel [email protected] 1
Department of Plant and Environmental Sciences, Clemson University, Clemson, SC 29634, USA
2
Department of Plant Pathology, The Ohio State University, Wooster, OH 44691, USA
Management of Anthracnose fruit rot is primarily based on chemical applications. In the USA, broad spectrum fungicides such as thiram and captan are registered for disease control and they both provide reasonable levels of protection against anthracno
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