Abstract
Stem-end rot (SER) caused by Lasiodiplodia theobromae is an important disease of mango in China. Demethylation inhibitor (DMI) fungicides are widely used for disease control in mango orchards. The baseline sensitivity to difenoconazole of 138 L. theobromae isolates collected from mango in the field in 2019 was established by the mycelial growth rate method. The cross-resistance to six site-specific fungicides with different modes of action were investigated using 20 isolates randomly selected. The possible mechanism for L. theobromae resistance to difenoconazole was preliminarily determined through gene sequence alignment and quantitative real-time PCR analysis. The results showed that the EC50 values of 138 L. theobromae isolates to difenoconazole ranged from 0.01 to 13.72 µg/mL. The frequency of difenoconazole sensitivity formed a normal distribution curve when the outliers were excluded. Difenoconazole showed positive cross-resistance only with the DMI tebuconazole but not with non-DMI fungicides carbendazim, pyraclostrobin, fludioxonil, bromothalonil, or iprodione. Some multifungicide-resistant isolates of L. theobromae were found. Two amino acid substitutions (E209k and G207A) were found in the CYP51 protein, but they were unlikely to be related to the resistance phenotype. There was no alteration in the promoter region of the CYP51 gene. However, difenoconazole significantly increased the expression of the CYP51 gene in the resistant isolates compared to the susceptible isolates. These results are vital to develop effective mango disease management strategies to avoid the development of further resistance.
Highlights
Stem-end rot (SER) caused by Lasiodiplodia theobromae is an important disease of mango in China
Demethylation inhibitor (DMI) fungicides are classified as a medium risk for resistance development by the Fungicide Resistance Action C ommittee[21]
DMIs fungicides were more favoured by orchardist due to their specific mode of action and broad anti-fungi spectrum at present
Summary
Stem-end rot (SER) caused by Lasiodiplodia theobromae is an important disease of mango in China. Difenoconazole significantly increased the expression of the CYP51 gene in the resistant isolates compared to the susceptible isolates These results are vital to develop effective mango disease management strategies to avoid the development of further resistance. In Hainan, Lasiodiplodia theobromae is the main pathogen causing stem-end rot (SER) of m ango[3]. This fungus may establish itself in the field asymptomatically and stay in a quiescent state. In Hainan Province, China, many DMI fungicides have been frequently used to control various diseases during mango cultivation placing great pressure on the selection of fungicides for L. theobromae and generating the risk of serious resistance of this pathogen to fungicides. Description Amplification of the promoter region of the Lt CYP51 gene Amplification of the coding region of the Lt CYP51 gene Quantitative RT-PCR primers for analysis of Lt CYP51 expression Amplification of the actin gene difenoconazole and other DMIs or fungicides that have different mechanisms of action than difenoconazole; and (III) investigate the molecular mechanisms that may be responsible for difenoconazole resistance
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