Journal
PLANT DISEASE
Volume 105, Issue 7, Pages 1936-1941Publisher
AMER PHYTOPATHOLOGICAL SOC
DOI: 10.1094/PDIS-07-20-1621-RE
Keywords
fludioxonil; fungicide resistance; resistance mechanism; Sclerotinia sclerotiorum
Categories
Funding
- Key Scientific and Technological Research Project of Henan Province [192102110056, 192102110030]
- First-Level Key Discipline Project of Plant Protection in Henan Province [107020219001/005]
- undergraduate innovation and entrepreneurship training program in Henan Province [S202010467002]
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The study found significant fitness costs associated with fludioxonil resistance in laboratory mutants of Sclerotinia sclerotiorum, leading to reduced mycelial growth, sclerotia formation, and pathogenicity. The mutants also showed increased sensitivity to osmotic stress and mutations in genes related to the HOG1-MAPK pathway. Additionally, positive cross-resistance was observed between fludioxonil and dimethachlone and procymidone, highlighting the potential for integrated pest management to mitigate fludioxonil resistance in field populations of S. sclerotiorum.
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, reports indicate that there is also 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 < 0.05) reduced mycelial growth and sclerotia formation on potato dextrose agar 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 of potassium chloride and 1.0 M of glucose), which is consistent with the proposed fludioxonil target sites within the high osmolarity glycerol stress response mitogen-activated protein kinase (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 that may be associated with fludioxonil resistance. For example, six separate point mutations were found in SsHk that led to changes in the predicted amino acid sequence, including A136G, F249V, G353A, E560K, M610K, and K727R. Similarly, SsPbs had three mutations (D34G, S46L, and L337E), SsSk1 and SsYpd had two (S53G and A795V for SsSk1, and E67G and Y141H for SsYpd), and SsHog and SsSk2 had one each (V220A and S763P, respectively). To our knowledge, these constitute the first reports of amino acid changes in proteins of the HOG1-MAPK pathway being associated with fludioxonil resistance in S. sclerotiorum. This study also showed 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 resistance developing in field populations of S. sclerotiorum and ensure the sustainable production of soybeans in China into the future.
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