Resistance to the SDHI Fungicides Boscalid and Fluopyram in Podosphaera xanthii Populations from Commercial Cucurbit Fields in Spain

Abstract

Powdery mildew is caused by Podosphaera xanthii, and is one of the most important diseases that attacks Spanish cucurbit crops. Fungicide application is the primary control tool; however, its effectiveness is hampered by the rapid development of resistance to these compounds. In this study, the EC50 values of 26 isolates were determined in response to the succinate dehydrogenase inhibitor (SDHI) fungicides boscalid and fluopyram. From these data, the discriminatory doses were deduced and used for SDHI resistance monitoring during the 2018 and 2019 growing seasons. Of the 298 isolates analysed, 37.9% showed resistance to boscalid and 44% to fluopyram. Although different phenotypes were observed in leaf disc assays, the resistant isolates showed the same phenotype in plant assays. Compared to sensitive isolates, two amino acid changes were found in the SdhC subunit, A86V and G151R, which are associated mostly with resistance patterns to fluopyram and boscalid, respectively. Furthermore, no significant differences were observed in terms of fitness cost between the selected sensitive and resistant isolates analysed here. Lastly, a loop-mediated isothermal amplification (LAMP) assay was developed to detect A86V and G151R mutations using conidia obtained directly from infected material. Our results show that growers could continue to use boscalid and fluopyram, but resistance management practices must be implemented.

Chitin Deacetylase, a Novel Target for the Design of Agricultural Fungicides

“…From these observations, we concluded that the chelating activity of EDTA was not responsible for fungal growth inhibition in these experiments. Furthermore, molecular docking experiments showed that the most likely site of binding of EDTA to the CDA protein is the chitin deacetylase domain in the enzyme catalytic pocket, suggesting that the inhibitory role of EDTA could be associated with its ability to interact with the CDA protein, as demonstrated for other carboxylic acids [34,40,41]. These results supported a direct interaction between the EDTA molecule and CDA protein and suggested the role of EDTA as a CDA inhibitor.…”

“…Due to their epiphytic parasitic nature, powdery mildews are easy targets for fungicides. In fact, chemical control is the main control tool of most powdery mildew diseases [40]. Once the important role played by CDA in disease establishment had been demonstrated, we conducted a search for molecules that could inhibit its activity under the premise that inhibition of CDA activity should also result in the suppression of fungal growth.…”

Assessing boscalid efficacy and resistance of large-spored Alternaria pathogens of potato and tomato crops

“…However, the sustained use of any fungicide most naturally raises concerns about the potential development of resistance in the target pathogens . Resistance to boscalid has been documented in various fungal species in diverse agricultural settings (Rosenzweig et al, 2008, Vielba-Fernández, et al, 2021. Resistance development can compromise the effectiveness of boscalid, rendering it ineffective in controlling early blight.…”