温度处理和茎尖培养结合脱除泡桐丛枝病类菌原体（MLO）

ELIMINATION OF MLOS FROM PAULOWNIA TISSUE CULTURE BY MEANS OF THERMOTHERAPY COMBINED WITH STEP TIP CULTURE

将患有丛枝病的泡桐组培苗进行温度处理，结合茎尖培养用来脱除病原ＭＬＯ。结果表明，在４５℃下，病茎段２４—４８小时内脱水枯死；在４０℃下３周内病苗黄化枯萎；但在３０℃和２５℃处理的茎段萌发新枝条仍表现典型丛枝症状。而在３５℃下处理的茎段，１周后，新生长茎叶外观恢复正常，继续处理至８０天，植株仍能正常生长。组织经ＤＡＰＩ染色后荧光显微镜检查显示出在３５－４０℃下处理的病苗体内ＭＬＯ４周之内的变化和降解情况。分别剪取３５℃下处理２９、３３、５５和８０天的组培苗０．５ｃｍ的茎尖，转入ＭＳ培养基或改良的ＭＳ培养基上，在２５℃下培养，长成的组培苗一直生长正常。荧光显微镜和电镜检察结果均显示病原ＭＬＯ已被脱除。

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.