Abstract: By means of stem tip culture after temperature treatment, the MLO-free plantings were obtained from witches'broom diseased Paulownia tissue culture.1cm long stem segments with two sidebuds were cultured in MS medium,and incubated in the growth chambers at different temperatures.Tee results showed that all the stem segments died in 24-48 hours at 45℃,and within 3 Weeks at 40℃.On the otherhand, the new shoots sprouted from the stem segments, but these still showed typical witches' broom symptoms at 30℃ for 5 weeks. When the stem segments infected with MLO were cultured at 35℃,the apparently healthy shoots sprouted and retained their form more than 178 days.Fluorescence Microscopy revealed that the MLO fluorescence could not be detected in tile sieve tubes of the newly sprouted shoots within 35-40℃ treatments and the intensity of fluorescence in the original stem segments was reduced gradually from 1 to 4 weeks.The stem tips(0.5cm long)were taken as explants from these treated tissue culture at 35℃ for 29,33,55 and 80 days,and then transformed into MS or modified MS medium again.Apparently healthy roots and shoots developed from all these explants at 25℃.The detection with fluorescence microscopy and electron microscopy showed that all such plants had been free from MLO.

Key words: Paulownia witches'broom, Mycoplasma-like organism(MLO), temperature treatment, stem tip culture