Abstract: To get loose, homogeneous, embryonic callus(LHEC) from Populus×canadensis Moench ‘Tower’, an efficient system was set up from the loose callus induction(LC) to successive transfer culture and embryonic callus induction with leaves of seedlings in tube and different kinds and concentration of hormones(BA,KT,2,4-D), sucrose and inorganic salt. The loose, homogeneous callus(LC) was induced completely(induction rate of 100%) with leaves and on the culture medium of low sugar and low inorganic salt(1/4MS+2 mg·L^-1 2,4-D+1 mg·L^-1 BA+10 g·L^-1 sugar). The globule embryonic callus(formerly embryoid) was induced after LC was transferred for 2-3 times on successive culture medium(MS+2.0 mg·L^-1 2,4-D+2.0 mg·L^-1 BA+Vc 100 mg·L^-1+30 g·L^-1), then transferred onto the medium of LHEC(MS+0.5 mg·L^-1 2,4-D+3 mg·L^-1 BA+Vc 100 mg·L^-1+40 g·L^-1 sucrose), and cultivated for 4-5 weeks(one time transfer every seven days). The cells of LC was kept in the characteristics of loose without roots, browning and with fast growth under the appropriate concentration of 2,4-D and BA. LC grew better and LHEC was produced more in medium containing 30 g·L^-1 sucrose. Vitamin C suppressed browning of LC in subculture. BA was conducive to the formation of LC, but KT was beneficial to the formation of compact callus, while the callus growth was faster by treatment of BA than by KT. When the concentration of 2,4-D was 0.5-1 mg·L^-1, the number of LHEC was increased with the increase of BA concentration. The number of LHEC reached to the maximum of 100%, when BA was 3 mg·L^-1. The main factors were discussed in callus embryogenic.

Key words: sucrose, culture system, inorganic salt, hormone, embryoid