Role of single site-specific allele replacement into svhk1 locus in the study of Stemphylium vesicarium dicarboximide and phenylpyrrole fungicides resistance

Stemphylium vesicarium is the fungal agent of pear Brown Spot and its resistance to dicarboximide fungicides has been a known concerning phenomenon since the 1990s. Henceforward, pear orchards have been monitored and field strains have been tested by mycelial growth inhibition assays to understand the sensitivity to dicarboximide and phenylpyrrole fungicides. Four phenotype classes were recognized according to in vitro responses to procymidone and iprodione: S (sensitive), S+ (low resistance), R1 (moderate resistance), R2 (high resistance). Cross-resistance to fludioxonil was only detected in R2 phenotype. Previous molecular studies correlated dicarboximide resistance class with single aminoacid substitutions observed in a two-component histidine kinase (HK1), corresponding to single nucleotide polymorphism (SNPs) in the nucleotidic sequence of SvHK1 gene (Alberoni et al., 2010). The goal of this ongoing study is to define the role of known SNPs in SvHK1 sequence on dicarboximide resistance by the replacement of the S allele with S+, R1 or R2 alleles. ...........................