Abstract: The isoelectric focusing gel electrophoretic approach was used in this study to compare the peroxidase isozyme bands of wheat varieties, which were either resistant or susceptible to powdery mildew.Great difference was found in the pI 6.1 band of peroxidase isozyme in leaves of resistant/susceptible varieties from the jointing stage to the occurrence of powdery mildew.The genes of the pI 6.1 band in the resistant varieties had a life-long normal expression.This band had a strong activity in the whole growing period of wheat and belonged to the first-class band category.When the expression was suppressed after the jointing stage of the susceptible varieties, resulting in ambiguity or even disappearance of the band, the band often belonged to the category of Class 3 or Class 0 bands.The enzyme gained activity after the infection of powdery mildew, resulting in the formation of Class 1 or Class 2 bands.In order to find the factors causing this difference, the peroxidase isozyme IEF bands in leaves were compared between the 119 F2 plants of resistant/susceptible varieties and the 65 BC1 plants of resistant/susceptible varieties.Results show that the decrease in the activity of the pI 6.1 band in susceptible adult plants is caused by another recessive gene.

Key words: Wheat, Peroxidase isozyme, Biochemical marker