Wild Type Sensitivity and Mutation Analysis for Resistance Risk to Fluopicolide in Phytophthora capsici

Abstract

Lu, X. H., Hausbeck, M. K., Liu, X. L., and Hao, J. J. 2011. Wild type sensitivity and mutation analysis for resistance dsk to fluopicolide in Phytophtlwra capsici. Plant Dis. 95:1535-1541.Crown, root, and fruit rot caused by Phytophthora capsici is an increasing problem for vegetable growers in Michigan and the United States. The newly registered fungicide tluopicolide is effective to limit crop loss but the potential for P. capsici to develop resistance is not well known. A laboratory study assessed the risk of P. capsici developing resistance to fluopicolide. Baseline sensitivity to fluopicolide was determined using 126 P. capsici Michigan isolates. Values of effective concentrations for 50% inhibition of mycelial growth ranged from 0.08 to 0.24 |ig/ml and were distributed as a unimodal curve, indicating that all isolates were sensitive to fluopicolide. Mutants resistant to fluopicolide were obtained from five isolates by screening zoospores on fluopicolide-amended (5 |ig/ml) media at a mutation frequency above 1.0 X 10"^. The mutant isolates were clustered with either intermediate (resistance factor [RF] = 3.53 to 77.91) or high (RF = 2481.40 to 7034.79) resistance. Resistance was stable through 10 mycelial transfers on fungicide-free medium. All resistant mutants showed similar fitness in zoospore production, cyst germination, and virulence compared with their sensitive parents, with tew exceptions. No cross-resistance was detected between tluopicolide and five other fungicides. There could be a moderately high dsk of field populations of P. capsici developing resistance to fluopicolide, and populations should be monitored.

Evaluation of New Oomycota Fungicides for Management of Phytophthora Root Rot of Citrus in California

“…The four new Oomycota fungicides are single-site mode of action inhibitors (Blum et al 2010;Pasteris et al 2016;Toquin et al 2006;Uchida et al 2005). Their resistance risk currently has not been completely characterized (FRAC 2018), and resistant field isolates have not yet been detected in Phytophthora species (Gisi and Sierotzki 2015;Lu et al 2011;Saville et al 2015). Resistance, however, has been described for Plasmopara viticola, another Oomycota organism, to mandipropamid (Gisi et al 2007).…”

Genetically Diverse Long-Lived Clonal Lineages ofPhytophthora capsicifrom Pepper in Gansu, China

“…The large pepper farms in Wuwei and Tianshui with a higher proportion of resistant isolates develop new capsicum varieties and fungicides are applied frequently. Because many areas have sensitive isolates, mefenoxam or metalaxyl fungicides may be useful, although fungicide rotation using chemistries with different modes of action should be used to slow the inevitable development of resistance (29,31).…”

Sensitivity of Different Developmental Stages and Resistance Risk Assessment of Phytophthora capsici to Fluopicolide in China

“…The initial RFs of 44 mutants ranged from 6.21 to 559.90 (Supplementary Table S2). The resistance levels to fluopicolide were artificially considered as intermediate resistance if RF was less than 100 and high resistance if RF was more than 100 (Lu et al, 2011). According to this division, 30 intermediately resistant mutants and 14 highly resistant mutants made up the 44 fluopicolide-resistant mutants.…”

“…The fungicide resistance risk assessment is essential to prevent or delay the development of fungicide resistance (Grimmer et al, 2014) and is mainly focused on the establishment of baseline sensitivity of sensitive pathogens, selection of resistant mutants, and evaluation of mutants' resistance level, stability, and fitness, as well as the cross-resistance between the target fungicide and several others (Miao et al, 2016). At present, the resistance risk of P. capsici to fluopicolide in Michigan in the United States has been analyzed by Lu et al (2011), and a few reports have described the sensitivity of P. capsici to fluopicolide in China using a limited number of isolates obtained from fewer than five provinces (Zhai et al, 2014;Wang et al, 2019). The objective of this study was to assess the resistance risk of P. capsici to fluopicolide in China in relation to the above aspects.…”