Abstract:In order to study the genetic transformation of Malus xiaojinensis Cheng et Jiang by Ri plasmid of Agrobacterium rhizogene.Factors affecting the transformation were studied by infection of Agrobacterium rhizogene.The results showed that strains and concentration of Agrobacterium rhizogene,kinds of explants,infection time,co-cultivation time and basal medium influenced the efficiency of hairy root formation strikingly,while 20mg/L acetosgringone had little effect on transformation.Leaf discs dipped into 8196 bacteria solution which diluted 5 times at exponential phase for 5～10min,co-cultured on MS medium for two days and transferred to 1/4MS medium plus kan(10mg/L) and cefotaxime(250mg/L) for one month was very useful for transformation.A highest frequency as 93.3 % of hairy roots inducing rate was achieved at the optimum conditions,96 % of hairy roots were positive in GUS histochemical identification of 50 hairy roots and 100% in PCR amplification of 48 GUS positive hairy roots.The high frequency of hairy roots inducing rate is propitious to regeneration of hairy roots and genetic transformation.