| Field isolates of Sclerotinia sclerotiorum from Jiangsu province were monitored for the fungicide resistance employing 5.0 mg.L-1 Carbendazim(MBC) in recent three years(2001-2003). The results indicated: that the rate of resistant isolates to MBC were increasing. This paper analyzed the growing causes of the rate of resistance to MBC.According to the FAO (1982) method, all the resistant phenotypes of field isolates of S.sclerotiorum to MBC were very high resistance (MBCVHR). Further study indicated that the phenotypes sensitive to MBC were diversified: isolates which failed to grow on media amended with 1.0mg.L-1 MBC ( MIC<1.0 mg.L-1 ) were considered assensitive(MBC ).Resistant isolates were divided into two phenotypes: high resistance (MBCHR), good growth on media amended with 1.0mg.L-1 MBC but not with containing 500 mg.L-1 MBC(1.00.5mg.L-1).MBCs and MBCHR isolates were insensitive to NPC except one isolates (JD2-3). MBCVHR isolates were all sensitive to NPC. There was obviously negative cross resistance (NCR) between MBC and NPC. Meantime, the only one isolate was detected, which phenotype sensitive to both MBC and NPC.Nucleotide sequence analysis revealed point mutation in the p-tubulin gene of MBC -resistant strains of S.sclerotiorum. Codon 198 for Glutamine acid (encode by GAG) was altered to Alanine (encode by GCG) in phenotypes sensitive strain of MBCVHRNPCS; and codon 200 for Phenylalanine (encode by TTC) altered to Tyrosine (encode by TAC) in phenotypes sensitive strains of MBCHRNPCVHR .No point mutation were taken place inphenotypes sensitive strains of MBCSNPCVHR. Mutation in 198 and 200 codon of p-tubulin gene was the molecular mechanism diversity to MBC -resistant of S. sclerotiorum. |
