Exploring the Biological and Molecular Characteristics of Resistance to Fludioxonil in Sclerotinia sclerotiorum From Soybean in China

Abstract

Sclerotinia sclerotiorum is one of the most damaging and economically important necrotrophic plant pathogens, infecting more than 400 plant species globally. Although the phenylpyrrole fungicide fludioxonil has high activity against S. sclerotiorum, recent reports have indicated that there is also a substantial potential for the development of fungicide resistance. However, the current study investigating five fludioxonil-resistant laboratory mutants found a significant fitness cost associated with fludioxonil resistance resulting in significantly (p < 0.005) reduced mycelial growth and sclerotia formation on PDA, as well as significantly (p < 0.05) lower pathogenicity on detached tomato leaves, with one mutant, LK-1R, completely losing the capacity to cause infection. In addition, all of the fludioxonil-resistant mutants had significantly (p < 0.05) increased sensitivity to osmotic stress (0.5 M KCl and 1.0 M Glucose), which is consistent with the proposed fludioxonil target sites within the High Osmolarity Glycerol (HOG1) stress response mitogen-activated protein kinase (MAPK) (HOG1-MAPK) signaling transduction pathway. Sequence analysis of six genes from this two-component pathway, including SsHk, SsYpd, SsSk1, SsSk2, SsPbs, and SsHog, revealed several mutations which maybe associated fludioxonil resistance. For example, six separate point mutations were found in the SsHk gene that lead to changes in the predicted amino acid sequence, including A136G, F249V, G353A, E560K, M610K, and K727R. Similarly, the SsPbs gene had three mutations (D34G, S46L, and L337E); the SsSk1 and SsYpd genes two (S53G and A795V, and E67G and Y141H, respectively) and the SsHog and SsSk2 genes one each (V220A and S763P, respectively). To the best of our knowledge, these constitute the first reports of amino acid changes in the proteins of the HOG1-MAPK pathway being associated with fludioxonil resistance in S. sclerotiorum. The study also found a positive cross-resistance between fludioxonil and dimethachlone and procymidone, but none with tebuconazole or carbendazim, indicating that the inclusion of tebuconazole within an integrated pest management program could reduce the risk of fludioxonil developing in field populations of S. sclerotiorum, and ensure the sustainable production of soybeans in China into the future.

Antifungal Mechanism and Efficacy of Kojic Acid for the Control of Sclerotinia sclerotiorum in Soybean

“…At present, the management of S. sclerotiorum in soybean strongly relies on the use of chemical fungicides, such as carbendazim, fluazinam, prochloraz, and procymidone ( Miorini et al, 2021 ). However, none of them offer complete control and several resistant strains have been reported ( Mao et al, 2020 ; Zhou et al, 2020 ). Apart from the low efficacy of commercial fungicides, the management of S. sclerotiorum is a difficult task due to the pathogen’s wide host range, and its persistent resting structures, called sclerotia.…”

Molecular mechanism of reduced biological fitness of fludioxonil‐resistant strains of Botrytis cinerea based on transcriptome analysis

“…10 There are significant adaptation costs associated with the resistance of Sclerotinia sclerotiorum to fipronil resulting in reduced mycelial growth, sclerotia, and pathogenicity of potato dextrose agar. 20 Our previous study identified five different-point mutant resistant strains and their biological characteristics showed a decreasing trend. We sequenced the transcriptomes of these five-point mutant resistant strains to analyze the molecular mechanism of reduced fitness of fludioxonil-resistant B. cinerea strains at the whole-genome level to explore the molecular mechanism underlying the reduced biological fitness of B. cinerea resistant to fludioxonil.…”

Characterization of SsHog1 and Shk1 Using Efficient Gene Knockout Systems through Repeated Protoplasting and CRISPR/Cas9 Ribonucleoprotein Approaches in Sclerotinia sclerotiorum

“…13,14 The strains resistant to dicarboxamide fungicides contained mutations in the group III histidine kinase gene (HK1), Shk1 in S. sclerotiorum. 13,14 Additionally, histidine kinase gene deletion mutants demonstrated phenotypes of crossresistance to both fungicides. 15,16 The histidine kinase gene is a possible target of dicarboximide and phenylpyrrole fungicides and involved in the high osmolarity glycerol (Hog1) stress response mitogen-activated protein kinase (MAPK) signal transduction pathway.…”

“…sclerotiorum. − However, repeated use of these fungicides has led to the development of resistance in S. sclerotiorum. − In addition, strains that exhibited resistance to dicarboximide fungicides demonstrated resistance to fludioxonil and vice versa. , The strains resistant to dicarboxamide fungicides contained mutations in the group III histidine kinase gene (HK1), Shk1 in S. sclerotiorum. , Additionally, histidine kinase gene deletion mutants demonstrated phenotypes of cross-resistance to both fungicides. , …”