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BACKGROUND: Stem‐end rot caused by Lasiodiplodia theobromae is one of the most important diseases of papaya in northeastern Brazil. It can be controlled effectively by demethylation inhibitor (DMI) fungicides, but the occurrence of DMI resistance may decrease fungicide efficacy. RESULTS: Detached fruit studies revealed that isolates with EC50 values of 6.07 and 6.28 μg mL−1 were not controlled effectively, but reduced virulence and ability to grow at temperatures ranging from 12 to 32 °C suggesting fitness penalties were observed. Cross‐resistance was observed only between difenoconazole and propiconazole. The entire cytochrome P450 sterol 14α‐demethylase (LtCYP51) gene and its flanking regions were cloned. The gene was 1746 bp in length and contained three introns. The predicted protein contained 525 amino acids. Phylogenetic tree analysis showed that the LtCYP51 belongs to the CYP51B clade. No amino acid variation was found between sensitive and resistant isolates; however, the gene was constitutively more highly expressed in resistant isolates. CONCLUSION: Resistance to DMI fungicides in L. theobromae is based on LtCYP51 gene overexpression and fitness penalties may be present in difenoconazole‐resistant isolates. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The role of the 14[alpha]-demethylase gene (MfCYP51) and the ATP-binding cassette transporter gene MFABC1in conferring demethylation inhibitor (DMI) fungicide resistance in field isolates with resistance to propiconazole is examined. The results have shown that overexpression of the MfCYP51 gene is very important in conferring DMI fungicide resistance in Monilinia fructicola field isolates from Georgia and that this overexpression is correlated with Mona located upstream of the MfCYP51 gene.

BACKGROUND: The increasing use of demethylation inhibitor (DMI) fungicides for the control of peach brown rot has resulted in resistance in Monilinia fructicola. Resistance in the southeastern USA is caused by overexpression of the MfCYP51 gene due to the presence of a 65‐bp inserted element 'Mona' located in the upstream regulatory region of MfCYP51. A rapid diagnostic assay would be useful to detect the presence and monitor further spread of this resistance mechanism. RESULTS: A loop‐mediated isothermal amplification (LAMP) method was developed for rapid detection of 'Mona'‐based DMI resistance. The assay was optimized for specificity and sensitivity, and was shown to detect the presence of 10 fg of purified target DNA per reaction within 85 min. Only DNA isolated from DMI‐resistant isolates containing 'Mona' resulted in a fluorescent signal after LAMP assay amplification. DNA from sensitive isolates from China and the USA and six other common fungal species of peach did not yield a signal. The method also positively identified 'Mona' from crude DNA extracts (using Lyse and Go reagents heated to 100 °C for 10 min) obtained from the mycelium and conidia of symptomatic fruit. CONCLUSION: Considering its specificity, stability and repeatability, the LAMP assay could be a valuable tool for rapid on‐site diagnosis of M. fructicola isolates resistant to DMI fungicides in the southeastern USA. © 2018 Society of Chemical Industry This article presents the development of a LAMP method to on‐site detect DMI fungicide resistance in Monilinia fructicola. [ABSTRACT FROM AUTHOR]

The genetic element 'Mona' has been shown previously to be associated with resistance to demethylation inhibitors (DMIs) in Monilinia fructicola. In this study, the promoter activity of the 'Mona' element was demonstrated genetically and the activity was narrowed down to a 20-bp active region through a series of deletions. 'Mona' knockout transformants (ΔMona) were generated from DMI-resistant isolate Bmpc7, and EC50 values and expression of the MfCYP51 gene were found to be reduced in transformants compared with the parental isolate. When the 'Mona' element was inserted into the upstream region of the MfCYP51 gene of the DMI-sensitive isolate HG3, the EC50 values and expression of the MfCYP51 gene increased in the transformants compared with the parental sensitive isolate. These results indicate that the 'Mona' element determines the DMI fungicide resistance through the up-regulation of the expression of the downstream MfCYP51 gene. No fitness penalty was observed in knockout and insertion transformants, i.e. transformants showed similar mycelial growth rate, sporulation and ability to cause lesions on fruit compared with their parental isolates, suggesting that the 'Mona' element does not affect basal life activities. [ABSTRACT FROM AUTHOR]

BACKGROUND The dicarboximide fungicide dimethachlone has been widely used in China for more than 12 years to control the Sclerotinia stem rot caused by Sclerotinia sclerotiorum disease. First signs of resistance in the field are reported at low frequency. In this study, four resistant isolate/mutants were used to explore still unknown mechanisms leading to dimethachlone resistance. RESULTS The resistant isolate/mutants had significantly higher EC50 values compared with the sensitive control isolates. Cross-resistance was confirmed between dimethachlone and procymidone, iprodione and fludioxonil. The resistant isolate/mutants revealed a decreased mycelial growth rate, were less pathogenic on leaves of oilseed rape, were more sensitive to osmotic pressure and oxidative stress and released more electrolytes compared with the sensitive isolates. Only in one lab mutant did we find a point mutation ( V238A) in the SsOs1 gene of the high-osmolarity glycerol ( HOG) signalling pathway. The expression of this gene was lost in the field resistant isolate HN456-1- JBJ and decreased in mycelium that was subjected to either high osmotic pressure or dimethachlone; however, another key gene in the HOG pathway, SsHog1, could be induced in the resistant isolate and mutants with NaCl treatment. CONCLUSION This study demonstrates that resistance to dicarboximide fungicide dimethachlone in S. sclerotiorum is emerging in China. Several fitness parameters, including mycelial growth rate, sclerotia formed in vitro, aggressiveness on leaves and osmotic and H2O2 sensitivity, indicate that the resistant strains may not effectively compete with sensitive isolates in the field in the absence of selection pressure. Lost expression or the V238A point mutation in the SsOs1 gene may confer resistance to dicarboximide fungicide dimethachlone in S. sclerotiorum, but this study illustrates that other, yet unknown mechanisms also exist. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]