The study was carried out to evaluate growth and genetic diversity among in vitro cultured protocorms of Cymbidiumspp. that irradiated with 10 Gy～300 Gy of electron beam. Shoot induction and shoot length were decreased by an increase ofintensity of electron beam, and shoot induction was significantly decreased over 200 Gy of electron beam irradiation in 10 weeksculture. As a result of ISSR (inter-simple sequence repeats) analysis, out of 80 bands detected overall, 10 bands were identifiedto be polymorphic with a rate of 12.5% at control group, and 90 bands detected overall, 38 bands were identified to bepolymorphic with a rate of 42.2% at electron beam treatment. According to the RAPD (random amplified polymorphic DNA)analysis, out of 92 bands detected overall, 12 bands were identified to be polymorphic with a rate of 13.0% at control group,and 121 bands detected overall, 53 bands were identified to be polymorphic with a rate of 43.8% at electron beam treatment.Genetic similarity matrix (GSM) of electron beam treatment was lower than that of control. The result indicates that the beamtreatment accelerated genetic diversity by promoting polymorphism of DNA. According to the cluster analysis by using both ISSRand RAPD markers, individuals of C. spp. were divided into control and electron beam treatment group. Our results indicatethat the electron beam irradiated in vitro cultured C. spp. might be resulted in promoting higher polymorphism but decreasingGSM.
