Abstract: Purpose:The formation of red color on the colony of T.rubrum is an important character for the identification of the fungus.But,those strains which cannot yield red color on the colony are isolated frequently.It is important to investigate the range,frequency and influence factors of the color variation of T.rubrum for the identification of the fungus and directing therapy.Method:200 strains of T.rubrum from different areas of China were isolated as the first generation and cultured serially.The resumptive actions of culture media (DCTA and PDA) on yielding color were observed,and the influences of different culture conditions on the color variation were compared.Result:The color variation rate of the first generation was 34% in 200 strains tested.The color variation rate induced by serial cultures was 49%.The majority variations induced by serial cultures were reversible,but the majority variations of the first generation were irreversible.Higher pH value of the cultures and lower cultural temperature were unfavorable in the formation of red color.The color variation rate of isolates from the North China was markedly higher than those from the South China.Conclusion:The frequency of color variation of T.rubrum is high that influences the identification of the fungus.The definite mechanism of the color variation remains to be studied.

Key words: Trichophyton rubrum, Phenotype, Variation