Baseline Pydiflumetofen Sensitivity of Fusarium pseudograminearum Isolates Collected from Henan, China, and Potential Resistance Mechanisms

Analysis of resistance risk and mechanism of the 14α-demethylation inhibitor ipconazole in Fusarium pseudograminearum

Ipconazole is a broad-spectrum triazole fungicide that is highly effective against Fusarium pseudograminearum. However, its risk of developing resistance and mechanism are not well understood in F. pseudograminearum. Here, the sensitivities of 101 F. pseudograminearum isolates to ipconazole were investigated, and the average EC50 value was 0.1072 μg/mL. Seven mutants resistant to ipconazole were obtained by fungicide adaption, with all but one showing reduced fitness relative to the parental isolates. Cross-resistance was found between ipconazole and mefentrifluconazole and tebuconazole, but none between ipconazole and pydiflumetofen, carbendazim, fludioxonil, or phenamacril. In summary, these findings suggest that there is a low risk of F. pseudograminearum developing resistance to ipconazole. Additionally, a point mutation, G464S, was seen in FpCYP51B and overexpression of FpCYP51A, FpCYP51B and FpCYP51C was observed in ipconazole-resistant mutants. Assays, including transformation and molecular docking, indicated that G464S conferred ipconazole resistance in F. pseudograminearum.

Survey of prothioconazole sensitivity in Fusarium pseudograminearum isolates from Henan Province, China, and characterization of resistant laboratory mutants

BACKGROUND

Fusarium crown rot (FCR) is one of the most significant diseases limiting crop production in the Huanghuai wheat-growing region of China. Prothioconazole, a triazole sterol 14α-demethylation inhibitor (DMI) fungicide developed by the Bayer Crop Protection Company, is mainly registered for the prevention and control of wheat powdery mildew and stripe rust (China Pesticide Information Network). It is known to exhibit high activity against F. pseudograminearum, but further research, particularly regarding the potential for fungicide resistance, is required before it can be registered for the control of FCR in China.

RESULTS

The current study found that the baseline sensitivity of 67 field isolates of F. pseudograminearum collected between 2019 and 2021 ranged between 0.016-2.974 μg/mL, with an average EC50 value of 1.191 ± 0.720 μg/mL (mean ± SD). Although none of the field isolates exhibited signs of resistance, three highly resistant mutants were produced by repeated exposure to prothioconazole under laboratory conditions. All of the mutants were found to exhibit significantly reduced growth rates on potato dextrose agar (PDA), as well as reduced levels of sporulation, which indicated that there was a fitness cost associated with the resistance. However, inoculation of wounded wheat coleoptiles revealed that the pathogenicity of the resistant mutants was little affected or actually increased. Molecular analysis of the genes corresponding to the prothioconazole target protein, FpCYP51 (FpCYP51A, FpCYP51B, and FpCYP51C), indicated that the resistant mutants contained three conserved substitutions (M63I, A205S, and I246V) that were present in the FpCYP51C sequence of all three mutants, as well as several non-conserved substations in their FpCYP51A and FpCYP51B sequences. Expression analysis revealed that the presence of prothioconazole (0.1 μg/mL) generally resulted in reduced expression of the three FpCYP51 genes, but that the three mutants exhibited more complex patterns of expression that differed in comparison to their parental isolates. The study found no evidence of cross-resistance between prothioconazole and any of the fungicides tested including three DMI fungicides tebuconazole, prochloraz, and flutriafol.

CONCLUSIONS

Taken together these results not only provide new insight into the resistant mechanism and biological characteristics associated with prothioconazole resistance in F. pseudograminearum, but also strong evidence that prothioconazole could provide effective and sustained control of FCR, especially when applied in combination with other fungicides.

Physiological mechanism of sodium salicylate and folcisteine on alleviating salt stress in wheat seedlings

Soil salinization substantially hampers the growth and development of wheat, potentially leading to plant death in severe cases, thus reducing grain yield and quality. This phenomenon poses a significant threat to food security in China. We investigated the effects of two exogenous plant growth regulators, sodium salicylate and folcisteine, on the wheat physiology and key characteristics under salt stress using hydroponics method. The results indicated that both regulators effectively mitigated the growth inhibition of wheat under salt stress. We assessed morphological and physiological indexes, including antioxidant enzyme activities (superoxide dismutase [SOD], catalase [CAT], peroxidase [POD]) and malondialdehyde (MDA) concentration in wheat after foliar application of sodium salicylate and folcisteine under salt stress. The findings revealed that sodium salicylate was more effective than folcisteine. However, folcisteine showed superior performance in reducing hydrogen peroxide (H2O2) content and superoxide anion (O2-) level compared to sodium salicylate. Simultaneously, Concurrent application of both regulators synergistically enhanced their efficacy, yielding the most favorable outcomes. In addition, this study noted that while the initial effects of these regulators were not pronounced, their sustained application significantly improved wheat growth in stressful condition and alleviated the detrimental impacts of salt stress. This approach could effectively guarantee the food security and production in China.

Target and non-target site mechanisms of fungicide resistance and their implications for the management of crop pathogens

Fungicides are indispensable for high-quality crops, but the rapid emergence and evolution of fungicide resistance have become the most important issues in modern agriculture. Hence, the sustainability and profitability of agricultural production have been challenged due to the limited number of fungicide chemical classes. Resistance to site-specific fungicides has principally been linked to target and non-target site mechanisms. These mechanisms change the structure or expression level, affecting fungicide efficacy and resulting in different and varying resistance levels. This review provides background information about fungicide resistance mechanisms and their implications for developing anti-resistance strategies in plant pathogens. Here, our purpose was to review changes at the target and non-target sites of quinone outside inhibitor (QoI) fungicides, methyl-benzimidazole carbamate (MBC) fungicides, demethylation inhibitor (DMI) fungicides, and succinate dehydrogenase inhibitor (SDHI) fungicides and to evaluate if they may also be associated with a fitness cost on crop pathogen populations. The current knowledge suggests that understanding fungicide resistance mechanisms can facilitate resistance monitoring and assist in developing anti-resistance strategies and new fungicide molecules to help solve this issue. © 2023 Society of Chemical Industry.