The tissue culture conditions of fast-growing clone K2 and fodder-type clone K3 of Robinia pseudoacacia L. tetraploid were investigated using shoot sprouting in hydroponic growth chamber as explants. After disinfected by 70% ethanol then sterilized with NaClO solution containing 0.5% available chlorine,the explants should be initially cultured with MS medium (containing 30 g·L-1 sucrose and 6 g·L-1 agar,pH 5.8),and survival rate of K2 and K3 explants all reaches 90% in initial culture medium. The best proliferation medium of K2 adventitious bud is MS medium adding 0.3 mg·L-1 6-BA and 0.05 mg·L-1 NAA,with the highest proliferation coefficient of 5.29,and that of K3 is MS medium adding 1.0 mg·L-1 6-BA and 0.10 mg·L-1 NAA,with the highest proliferation coefficient of 3.36. The optimized rooting medium of K2 and K3 plantlets is 1/2MS medium (containing 30 g·L-1 sucrose and 6 g·L-1 agar,pH 5.8) adding 0.1 mg·L-1 IBA and 0.1 mg·L-1 NAA,respectively. After training,K2 and K3 plantlets are transplanted by two-step transplanting method,all of survival rate reach 98%.
Differences in drought tolerance were studied among three strains of black locust(Robinia pseudoacacia L.) clones(one-year-old micropropagated K2,K3 clones and a common diploid clone CK) under simulated natural drought conditions.The experiment was carried out as a randomized complete blocks design.The following physiological variables were examined,biomass and allocation,photosynthetic characteristics,i.e.net photosynthetic rate(Pn),transpiration rate(E),stomatal conductance(Gs),intercellular CO2 concentration(Ci),instantaneous water use efficiency(WUEI),and long-term water use efficiency(WUEL).Results showed that the K2 and K3 had greater biomass,with the K3 displaying favorable ratio of root biomass to shoot and leaf biomass.Net photosynthetic rate(Pn) declined along with Gs,Ci and the ratio intercellular/ambient(Ci/Ca),under increasing drought stress.The decline in photosynthesis was mainly due to stomatal limitation.The K2 and K3 showed higher WUE and Pn than the CK.There were significant differences of drought level on WUEL,and the WUEL of K2 and K3 was greater than that of CK.Evaluation based overall physiological characteristics indicates the K2 and K3 are more drought tolerant,which are well adapted to the drought-stricken area of Northwest China.
