Salt Tolerant Mutant Screening And RAPD Analysis On Apple Rootstock

Apple rootstocks were decisive in apple salt tolerance. Screening and breeding salt tolerant mutants could improve apple salt tolerant ability. Recently tissue culture and mutagenesis technique were used in screening salt tolerant mutant successful in many crops. But the mutant's reality was often doubtful, because it might not be genotype. So it is the most important to identify the genotype of the mutants.The research was carried out with two apple rootstocks: My and 78-48, as well as their salt tolerant regenerations. The mutants were screened were screende out by salt-stressed culture for many generations. The mutants were identified through RAPD technique. The main results were as follows:1.To obtain salt tolerant rootstocks, high level NaCl (0.8% & 1.0%) was added into the culture medium directly. Though salt stress culture for six successive generations, the salt tolerant mutants were obtained.2.The survival rate of two apple rootstocks and their mutants cultured on salt medium were higher than control, but the injury rate and injury index of mutants were lower than control. The mutants showed higher level of salt tolerance.3.A consistent amplication reaction system were established by adding 20uL mixture containing 1.25 units Taq DNA polymerase, 20ng template DNA, 0.25uM primer, 0.2mM dNTPs, 3.0mM Mg + and 1-fold Buffer. 45 amplified cycles were carried out with a set of PCR.4.Through RAPD analysis of rootstock M7 and its mutants, 5 out of 153 randomized primers could be detected to have DNA polymorphism of three mutated lines Z2, Z3 and Z5; 36 random primers could be detected to have DNA polymorphism of 78-48's mutated lines (L1, L2) definitely. Results showed the mutants varied at the DNA molecular level, which provided an evidence of the mutation. Further study is required to obtain the molecular marker of RAPD closely linked to the salt tolerant mutation locus.5.There were many indicators for salt tolerance identification. Discriminatory analysis showed that injury index could reflect the injuried degree of apple rootstocks under salt stress. So the injury index could be used as a morphological index to accurately evaluate the levels of salt tolerance of rootstocks. In earlier screening, the cell membrane permeability, MDA and Cl content, SOD and POD activity, and some other biochemical indicators could be used as references to assess salt tolerance. However, application ofmolecular marker techniques is a precise method to detect the mutant.