Abstract
Glomerella leaf spot (GLS), Glomerella fruit rot (GFR) and apple bitter rot (ABR), caused by Colletotrichum spp. are amongst the most devastating apple diseases in the southeastern United States. While several species have been identified as causal pathogens of GLS, GFR, and ABR, their relative frequency and fungicide sensitivity status in the southeastern U.S. is unknown. In total, 381 Colletotrichum isolates were obtained from symptomatic leaves and fruit from 18 conventionally managed apple orchards and two baseline populations in western North Carolina and Georgia in 2016 and 2017. Multilocus DNA sequence analysis revealed that C. chrysophilum was the predominant cause of GLS and GFR, and C. fioriniae was the causal agent of ABR. Baseline and commercial populations of Colletotrichum spp. were evaluated for sensitivity to pyraclostrobin and trifloxystrobin and no statistical differences in sensitivity between the two species were observed for conidial germination. However, EC50 values were significantly lower for C. fioriniae compared to C. chrysophilum for both fungicides regarding mycelial inhibition. Isolates recovered from commercial orchards revealed that 5 populations of C. chrysophilum and 1 population of C. fioriniae had reduced sensitivity to trifloxystrobin, and 1 C. fioriniae population had reduced sensitivity to pyraclostrobin via conidial germination assays. The cytb gene for 27 isolates of C. fioriniae, C. chrysophilum, and C. fructicola with different QoI sensitivities revealed the G143A mutation in a single isolate of C. chrysophilum with insensitivity to both fungicides. Results of these studies suggest that two Colletotrichum spp. predominantly cause GLS and ABR in the southeastern U.S. and that a reduction in sensitivity to some QoI fungicides may be responsible for control failures. This study also provides basis for monitoring shifts in QoI sensitivity in Colletotrichum spp. causing disease on apple in the southeastern U.S.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
