MfOfd1 is crucial for stress responses and virulence in the peach brown rot fungus Monilinia fructicola

Resistance to the DMI fungicide mefentrifluconazole in Monilinia fructicola: risk assessment and resistance basis analysis

BACKGROUND

Brown rot disease, caused by Monilinia fructicola, poses a significant challenge to peach production in China. The efficacy of mefentrifluconazole, a new triazole fungicide, in controlling brown rot in peaches has been remarkable. However, the resistance risk and mechanism associated with this fungicide remain unclear. This study was designed to assess the resistance risk of M. fructicola to mefentrifluconazole and reveal the potential resistance mechanism.

RESULTS

The mean median effective concentration (EC50 ) of 101 M. fructicola isolates to mefentrifluconazole was 0.003 μg mL-1 , and the sensitivity exhibited a unimodal distribution. Seven mefentrifluconazole-resistant mutants were generated from three parental isolates in the laboratory through fungicide adaption. The biological characteristics of the resistant mutants revealed that three of them exhibited enhanced survival fitness compared to the parental isolates, whereas the remaining four mutants displayed reduced survival fitness. Mefentrifluconazole showed strong positive cross-resistance with fenbuconazole, whereas no cross-resistance was observed with pyrimethanil, procymidone or pydiflumetofen. No overexpression of MfCYP51 gene was detected in the resistant mutants. Multiple sequence alignment revealed that three resistant mutants (MXSB2-2, Mf12-1 and Mf12-2) had a point mutation (G461S) in MfCYP51 protein. Molecular docking techniques confirmed the contribution of this point mutation to mefentrifluconazole resistance.

CONCLUSION

The risk of M. fructicola developing resistance to mefentrifluconazole is relatively low-to-medium and point mutation G461S in MfCYP51 could confer mefentrifluconazole resistance in M. fructicola. This study provided essential data for monitoring the emergence of resistance and developing resistance management strategies for mefentrifluconazole. © 2023 Society of Chemical Industry.

Stone fruit phenolic and triterpenoid compounds modulate gene expression of Monilinia spp. in culture media

Phenolic and triterpenoid compounds are essential components in stone fruit skin and flesh tissues. They are thought to possess general antimicrobial activity. However, regarding brown rot disease, investigations were only confined to a limited number of phenolics, especially chlorogenic acid. The activity of triterpenoids against Monilinia spp., as an essential part of the peach cuticular wax, has not been studied before. In this work, the anti-fungal effect of some phenolics, triterpenoids, and fruit surface compound (FSC) extracts of peach fruit at two developmental stages were investigated on Monilinia fructicola and Monilinia laxa characteristics during in vitro growth. A new procedure for assaying anti-fungal activity of triterpenoids, which are notoriously difficult to assess in vitro because of their hydrophobicity, has been developed. Measurements of colony diameter, sporulation, and germination of second-generation conidia were recorded. Furthermore, the expression of twelve genes of M. fructicola associated with germination and/or appressorium formation and virulence-related genes was studied relative to the presence of the compounds. The study revealed that certain phenolics and triterpenoids showed modest anti-fungal activity while dramatically modulating gene expression in mycelium of M. fructicola on culture medium. MfRGAE1 gene was overexpressed by chlorogenic and ferulic acids and MfCUT1 by betulinic acid, at 4- and 7- days of mycelium incubation. The stage II FSC extract, corresponding to the period when the fruit is resistant to Monilinia spp., considerably up-regulated the MfLAE1 gene. These findings effectively contribute to the knowledge of biochemical compounds effects on fungi on in vitro conditions.

Site-directed transformants with E407K substitution in Bcmdl1 possesses different fitness from field anilinopyrimidine resistant isolates with E407K mutation in Botrytis cinerea

Botrytis cinerea is the causal agent of devastating disease gray mold on numerous crops worldwide. To control gray mold, anilinopyrimidine (AP) fungicides have been widely applied since the 1990s. However, the development of resistance in B. cinerea brought a new challenge to this disease control. Due to the unknown mode of action, the mechanism of AP resistance is still ambiguous. In our previous study, mutation E407K in Bcmdl1 was identified to be associated with AP resistance. Since this mutation is the major mechanism of AP resistance in our cases, it is essential to investigate the fitness of E407K strains before designing anti-resistance management strategies. Besides using field-resistant isolates with the E407K mutation, strains with E407K substitution obtained by site-directed mutagenesis were also used to estimate the specific effect of this mutation or substitution on fitness. The fitness of E407K strains were evaluated by determining mycelial growth, sporulation, conidial germination, virulence, acid production, osmotic and oxidative sensitivity, and sclerotial production and viability. Field resistant isolates with E407K mutation produced fewer sclerotia on intermediate medium (IM) but more conidia on PDA when compared with sensitive isolates, whereas site-directed transformants with E407K substitution did not show any fitness costs. The competitive ability of E407K strains was also evaluated on apple fruit using conidial mixtures at three initial ratios of resistant and sensitive isolates at 1:9, 1:1, and 9:1, respectively. Similar with fitness, impaired competitive ability was observed in field resistant isolates but not site-directed transformants at all initial ratios tested. These results indicated that field strains associated with AP resistance suffer a fitness penalty not linked directly to the E407K substitution in Bcmdl1.

Spontaneous, Artificial, and Genome Editing-Mediated Mutations in Prunus

Mutation is a source of genetic diversity widely used in breeding programs for the acquisition of agronomically interesting characters in commercial varieties of the Prunus species, as well as in the rest of crop species. Mutation can occur in nature at a very low frequency or can be induced artificially. Spontaneous or bud sport mutations in somatic cells can be vegetatively propagated to get an individual with the mutant phenotype. Unlike animals, plants have unlimited growth and totipotent cells that let somatic mutations to be transmitted to the progeny. On the other hand, in vitro tissue culture makes it possible to induce mutation in plant material and perform large screenings for mutant’s selection and cleaning of chimeras. Finally, targeted mutagenesis has been boosted by the application of CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9 and Transcription activator-like effector nuclease (TALEN) editing technologies. Over the last few decades, environmental stressors such as global warming have been threatening the supply of global demand for food based on population growth in the near future. For this purpose, the release of new varieties adapted to such changes is a requisite, and selected or generated Prunus mutants by properly regulated mechanisms could be helpful to this task. In this work, we reviewed the most relevant mutations for breeding traits in Prunus species such as flowering time, self-compatibility, fruit quality, and disease tolerance, including new molecular perspectives in the present postgenomic era including CRISPR/Cas9 and TALEN editing technologies.