Studies On Browning Factors Of Explant And Proliferation Culture Of Walnut(Juglans Regia L.)

The micropropagation procedures of walnut (Juglans regia L.) and black walnut (Juglans negro L.) had been researched, including the factors affecting explants browning, the establishment of aseptic cultures, shoot proliferation, selection of suitable medium and hormone. A feasible and practical micropropagation system had been made.Factors affecting walnut browning are as follows: the time collect shoot affecting browning, in august, two species walnut both have the lowest browning rate; species also affecting browning, black walnut has a higher browning rate than walnut in the growth season; the older the age, the higher the browning rate; explants in 0.1%HgC12 less than 8 mins has a lower rate; PPO and browning rate's correlation is not significant; but phenol concentration and browning rate has a very significant correlation, (R=0.791**); add Vc in the medium can greatly reduce the mortality due to browning. High survival rate of the explants can be achieved when the explants of walnut were collected in May and explants of black walnut were collected in August. Washing the explants under running water and in 0. !%HgC12 for 8 min, rinsed 3-4time with sterile water, the survival rate was 51.62% and 42.86%. Walnut of mianhetao seedling in 0.1%HgC12 for 6min, baopihetao and lourenhetao seedling in 0.1%HgC12 for 4.5min. The survival rate was 85%and 66.7%and 40% respectly.Culture the survival stem on DKW medium with l.Omg/LBA and O.Olmg/LIBA can quickly made the bud germinate and growth well.During the shoot proliferation, DKW medium was more suitable for growth and subculture of the shoots than on MS and H medium. The exogenous application of cytokinins-BA was very necessary for shoot proliferation, 0.5-l.Omg/LBA have a higher proliferation rate, combination of cytokinin and lower concentration auxin-IB A can stimulate the growth of shoots. Thus the optimal proliferation medium was DKW medium supplement with l.Omg/LBA, O.Olmg/LIBA. It was good to keep the cultures at 22癈,16hr. photoperiod in the first 7 days, then at 25-26癈 in the middle phase, at 28 癈 in the last 7days, the proliferation rate can reached 4.6.Enlonger the last period to 12d,subcultures every 35d, have a proliferation rate 4.8.DKW medium added BA0.25mg/L, IBA0.03mg/L made the shoot elongation and better growth.