稻株上拮抗细菌的定殖及其对土著细菌的影响

Colonization of antagonistic bacteria on rice plants and their influence on native bacteria

在温室条件下，通过分批播种、接种纹枯病菌Rhizoctonia solani，以及在水稻分孽盛期喷雾拮抗细菌Pseudomonas fluorescensPf7—14（天然的抗萘啶酮酸菌株）和B5423．R（Bacillus subtilisB5423的利福平抗性突变体）的菌悬浮液，并通过定期取样，平板系列稀释法回收，测定了菌株Pf7-14、135423-R和土著细菌群体在水稻健株和纹枯病株上的种群数量，所获结果如下：①当相同的浓度（约2．0×10^8cfu／m1）的菌悬浮液喷雾到叶片时，菌株Pf7—14定殖的时间比菌株B5423-R长，且在相同的时间内，菌株Pf7—14的平均群体数量高于菌株B5423-R；②在健康的水稻茎部，菌株Pf7—14的两个高、低不同浓度处理的平均群体数量均表现出随时间降低的趋势；相比，较低浓度（4．0×10^7cfu／m1）的B5423-R在茎部的平均群体数量随着时间的下降，而较高浓度（2．0×10^8cfu／m1）的B5423-R的平均群体数量在水稻乳熟至黄熟期保持稳定或略有增长；③当病斑面积占取样茎面积的比率为20％～35％时，在应用1和14d后菌株PU-14在健茎的平均群体数量分别是病茎的6倍多和2倍多，差异均达到显著性的水平（P=0．05），而菌株B5423．R在应用1d后病茎的数量比在健茎显著性地低大约1倍，但在7～14d后，病茎的数量比在健茎显著性地高5～6倍，群体在病茎表现出相对的增长；④土著细菌群体在病斑茎部是健茎的6～7倍。这些结果表明两类拮抗细菌有着明显不同的定殖习性，在病斑上B5423比pf／-14具有更强的竞争能力，是一类更好的生防制剂；同时表明引入的拮抗细菌同土著细菌群体在营养和空间上竞争激烈，且土著细菌群体更具有竞争优势。

Abstract： Pseudomonas fluorescens strain Pf7-14 and Bacillus subitlis strain B5423, as biological control agents （BCA） of rice sheath blight, suppressed effectively Rhizoctonia solani AG 1, its causal pathogen. The average population sizes of strain Pf7-14, a strain naturally resistant to nalidixic acid, and strain B5423-R, a spontaneous rifampicin-resistant mutant of strain B5423 as well as native bacterial population （NBP） on rice plants, were monitored under greenhouse conditions by spraying the suspensions of strains Pf7-14 and B5423-R onto both healthy and R. solani AG1 inoculated rice plants. Strain B5423-R was as suppressive to R. solani AG1 and functioned as a biological control agent of rice sheath blight as its wild type. Based on periodically sampling of rice leaves and culms, and bacterial population estimated by method of dilution plate counting, the following results were obtained. On healthy leaves, the population sizes of strains PfT-14 were higher than those of strain B5423-R when the initial population of the two was similar. The population sizes on the culms of the rice plant, strains PfT-14 declined over time regardless of initial concentration. In contrast, the population of strain B5423- R declined over time when the initial concentration was low （4.0 × 10^7 cfu/ml or less） , but remained constant or increased slightly from milky to ripening stage of plant growth when a higher concentration of the bacterium （2.0 ×10^8 cfu/ml or more） was applied to the rice plants. In the batch of rice plants inoculated with R. solani AG1, at level of sheath blight lesions of 20%-- 35%, the average population sizes of strain Pf7- 14 were 6 and 2 times significantly lower than those on healthy culms, 1 day and 14 days after BCA application（P = 0.05）, respectively. Contrarily, the population size of strain B5423-R was about 1 time lower on diseased than on healthy culms at one day after its application. Henceforth however, the population of strain B5423-R increased, and it was 6 times significantly higher on diseased than on healthy culms measured at 14 days after its application. NBP was about 6 to 7 times significantly higher on diseased than on healthy culms. The ability to colonize healthy and diseased culms appears to be different between the two antagonistic bacteria. The results suggested that although both strains are originated from the same rice ecosystem, but differ in capacity of colonizing rice plant, that strain B5423-R, a bacillus, seems to be more competitive in diseased plants than strain Pf7-14, and that the introduced antagonistic bacteria （IAB） and NBP are competitive in nutrient and space each other, and NBP has an advantage over lAB in competition.