Fungicide resistance in Botrytis cinerea populations from vineyards in the table grape production regions of South Africa

PROJECT TITLE: Fungicide resistance in Botrytis cinerea populations from vineyards in the table grape production regions of South Africa

Project leader:  Dr Pieter Louw (Experico)

Duration: 1 November 2021 – 31 December 2023

Project Summary:

The loss of sensitivity towards fungicides or the development of fungicide resistance has become a concern to the table grape industry. Only a few active ingredients are available to control preharvest and postharvest diseases, making it difficult to rotate spray programmes. The primary at harvest and postharvest pathogen of table grapes is Botrytis cinerea, however, Alternaria, Aspergillus, Rhizopus and Penicillium species can also be problematic. Prominent active ingredients used by industry to control these and other pathogens include boscalid, cyprodinil, fenhexamid, fludioxonil, fluopyram, pyraclostrobin and pyrimethanil. B. cinerea has a high risk of developing resistance to fungicides (Angelini et al., 2014). This has been observed on cucumbers, tomatoes (Ren et al., 2016), raspberries, strawberries, cherries and table grapes (Angelini et al., 2014; Hahn and Leroch, 2015; Rupp et al., 2017). A survey in North Germany over several years (up to six years) revealed resistance build-up to fludioxonil in B. cinerea isolates from raspberry and strawberry fields. The resistance frequency in raspberry fields changed from ±6% to 90% in five years. The resistance frequency in strawberries was 80%. In the same survey, grapevine and cherry orchards were also assessed. No fludioxonil resistance was initially detected in grapevine and cherry orchards but it increased, potentially, due to the migration of resistant isolates from nearby strawberry fields (resistance frequency of 10 – 27%) (Rupp et al., 2017).
The loss of more active ingredients, not only due to market restrictions, but also due to fungicide resistance, can be detrimental to the South African table grape industry. Some preharvest fungicides have been available for numerous years, further increasing the risk of fungicide resistance build-up. This study aims to develop a tool to determine or monitor fungicide resistance in B. cinerea populations isolated from South African table grape vineyards. Three of the major production regions will be included in the study. This tool or method can eventually be used to frequently test for fungicide resistance in vineyards, equipping the producer and chemical advisor to make informed discissions to adapt spray programmes for more effective control and, if managed correctly, reduce resistance build-up.

References
▪ Cloete, B.P. 2018. Development of a fungicide resistance screening assay for the pome fruit pathogens Botrytis cinerea and Venturia inaequalis. MSc thesis. Stellenbosch University, Stellenbosch. ▪ De Miccolis Angelini, R.M., Rotolo, C., Masiello, M., Gerin, D., Pollastro, S. and Faretra, F. 2014. Occurrence of fungicide resistance in populations of Botryotinia fuckeliana (Botrytis cinerea) on table grape and strawberry in southern Italy. Pest Manag. Sci. 70, 1785-96. doi: 10.1002/ps.3711.

Version 2 updated 2018
▪ Förster, H., Driever, G.F., Thompson, D.C., and Adaskaveg, J.E. 2007. Postharvest decay management for stone fruit crops in California using the “reduced-risk” fungicides fludioxonil and fenhexamid. Plant Disease 91, 209-215.
▪ Hahn, M. and Leroch, M. 2015. Multidrug efflux transporters. In: Fungicide Resistance in Plant Pathogens, Ishii, H. and Hollomon, D.W. (eds.). pp. 233-250. Springer Science + Business Media, London.
▪ Lehner, M.S., Paula Júnior, T.J., Silva, R.A., Vieira, R.F., Carneiro, J.E.S., Schnabel, G. and Mizubuti, E.S.G. 2015. Fungicide Sensitivity of Sclerotinia sclerotiorum: A Thorough Assessment Using Discriminatory Dose, EC50, High-Resolution Melting analysis, and Description of New Point Mutation Associated with Thiophanate-Methyl Resistance. Plant Dis. 99, 1537-1543. doi: 10.1094/PDIS-11-14-1231-RE.
▪ Ren, W., Shao, W., Han, X., Zhou, M. and Chen, C. 2016. Molecular and biochemical characterization of laboratory and field mutants of Botrytis cinerea resistant to fludioxonil. Plant Disease 100, 1414-1423.
▪ Rupp, S., Weber, R.W.S., Rieger, D., Detzel, P. and Hahn, M. 2017. Spread of Botrytis cinerea Strains with Multiple Fungicide Resistance in German Horticulture. Front. Microbiol. 7, 2075. doi: 10.3389/fmicb.2016.02075