Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2019
Publication Date: 2/3/2020
Citation: Naegele, R.P., Delong, J.A., Saito, S., Xiao, C. 2020. Population genetics and fungicide resistance of Botrytis cinerea on Vitis and Prunus spp. in California. Phytopathology. 110(3):694-702. https://doi.org/10.1094/PHYTO-09-19-0362-R.
Interpretive Summary: Botrytis cinerea is a fungal pathogen that can cause disease on more than 200 crop species. In susceptible crops, industries rely heavily on chemical sprays to manage the disease. Fungicide resistance is common, and can develop even when using rotating chemicals with different modes of action. Genetic fingerprinting and fungicide resistance testing were used to track changes in field populations of Botrytis cinerea from grape, apricots and nectarines. The number of isolates with resistance to more than one fungicide increased between 2012 and 2017, but few genetic changes were found between the two years. There were no detected differences in Botrytis cinerea isolates from Prunus (apricot and nectarine) and grape, but the frequency of fungicide resistant isolates varied between crops.
Technical Abstract: Botrytis cinerea, the causal agent of gray mold, has high genetic diversity and a broad host range. In Vitis sp. and Prunus spp., B. cinerea causes pre- and postharvest diseases, and fungicides are routinely used to prevent yield loss. In total, 535 isolates of B. cinerea collected from Vitis sp. and Prunus spp. in 2012, 2016, and 2017 were genotyped using 18 microsatellite markers and the transposable elements (TE) Boty and Flipper. Only nine of the polymorphic markers, were considered informative and retained for the final analyses. Of the 535 isolates, 498 were tested for resistance to seven different fungicides, representing six chemical classes. After clone correction, 323 multi-locus genotypes (MLG) groups were retained across the three years, and four genetic subpopulations were detected. High levels of clonality were observed across the dataset. Significant pairwise differentiation was detected among years, locations, and TE composition. However, most of the differentiation observed was within a subpopulation, and not among subpopulations. No genetic differentiation was detected among resistant and sensitive isolates for individual fungicide classes. When resistance to the total number of fungicides was compared, regardless of the fungicide class, significant differentiation was detected among isolates that are resistant to two fungicide classes, and three or four fungicide classes.