Amplified fragment length polymorphism analysis was performed according to Vos et al (1995). Total genomic DNA from parents or each F2 individual was digested with EcoRⅠand MseⅠ(MBI Fermentas, UK) and the ligation with adaptors by T4 ligase (MBI Fermentas, UK) was performed simultaneously in 25 μL reaction mixtures, and the restriction-ligation reaction incubated at 37℃ for 12 h.