青枯雷尔氏菌Tn5转座子无致病力突变株在番茄根部的定殖特性

Colonization characteristics of Ralstonia solanacearum avirulent mutants yielded by Tn5 transposon in the tomato root

为筛选防治番茄青枯病的优良生防菌株,本研究以弱化指数、胞外多糖含量和盆栽苗番茄发病率为指标确定20株经形态初步判定为无致病力的青枯雷尔氏菌Ralstonia solanacearum Tn5突变菌株的致病性,测定其在番茄根部的定殖数量,并于显微镜下观察其定殖特性。结果表明,供试的20株青枯雷尔氏菌无致病力突变菌株的弱化指数均大于0.75,胞外多糖含量介于1.59~16.68µg/mL之间,显著低于强致病力菌株FJAT-91,接种40 d番茄植株未出现青枯病症状;20株青枯雷尔氏菌无致病力突变菌株均能在番茄根部定殖,定殖数量呈先上升后下降的趋势,其中菌株T659的定殖数量最大,定殖时间最长,分别为2.86×10^(6) CFU/g和35 d;透射电镜观察发现,青枯雷尔氏菌无致病力突变菌株T659从番茄植株根部表皮细胞中侵入,然后进入维管束厚壁细胞,并在维管束细胞中大量繁殖和定殖,但未引起番茄根部细胞结构病理变化。表明供试的青枯雷尔氏菌无致病力突变菌株T659的定殖能力最强,具有良好的生防潜力。

To screen for biocontrol agents against tomato bacterial wilt,Ralstonia solanacearum avirulent mutants yielded by Tn5 transposon was evaluated.First,20 R.solanacearum mutants yielded by Tn5 transposon were tested to determine their attenuation indexes(AI),extracellular polysaccharides(EPS)contents and wilt incidence of inoculated tomato seedlings.Then,the colonization of these mutants in the inoculated tomato roots were quantified by dilution plating of homogenized root tissues,and their colonization characteristics were observed with the transmission electron microscopic(TEM)technology.The results showed that the AI values of tested mutants were all above 0.75;EPS contents of the mutants were ranged from 1.59 to 16.68µg/mL,significantly lower than that of the virulent strain FJAT91(28.42µg/mL).Moreover,no symptoms of bacterial wilt were observed 40 d after the tomato plants were inoculated with all the avirulent mutants.All the tested mutants could colonize tomato roots with a trend of increasing first and then decreasing.Among them,the mutant T659 could colonize tomato roots well,had the highest quantity of 2.86×10^(6) CFU per gram root tissues,and the T659 cells in roots remained culturable the longest time of 35 d post-inoculation.Results from TEM observations revealed that T659 invaded the epidermal cells of tomato roots first,and then enter and multiply massively in the vascular cells,but no pathological structure changes were observed in the inoculated tomato root cells.The results suggested that the avirulent mutant T659 had the best colonization ability and a good biocontrol potential.