The auxin produced by epiphytic microbes aggravated russet severity by disrupting normal hormonal balance and altering the development of epidermal cells of immature fruit.The synthetic auxin such as naphthalene acetic acid was reported to induce the russeting in ‘Fuji’ apple (Jones et al., 1991). Therefore,fruit russeting is not only considered as a physiological disorder,but also as a pathogen-induced disease.