Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, The Robert H. Smith Faculty of Agriculture, Food, and Environment, Rehovot 76100, Israel.
Phytopathology. 2013 Jan;103(1):23-33. doi: 10.1094/PHYTO-12-11-0349.
Soil suppressiveness to Fusarium disease was induced by incubating sandy soil with debris of wild rocket (WR; Diplotaxis tenuifolia) under field conditions. We studied microbial dynamics in the roots of cucumber seedlings following transplantation into WR-amended or nonamended soil, as influenced by inoculation with Fusarium oxysporum f. sp. radicis-cucumerinum. Disease symptoms initiated in nonamended soil 6 days after inoculation, compared with 14 days in WR-amended soil. Root infection by F. oxysporum f. sp. radicis-cucumerinum was quantified using real-time polymerase chain reaction (PCR). Target numbers were similar 3 days after inoculation for both WR-amended and nonamended soils, and were significantly lower (66%) 6 days after inoculation and transplanting into the suppressive (WR-amended) soil. This decrease in root colonization was correlated with a reduction in disease (60%) 21 days after inoculation and transplanting into the suppressive soil. Fungal community composition on cucumber roots was assessed using mass sequencing of fungal internal transcribed spacer gene fragments. Sequences related to F. oxysporum, Fusarium sp. 14005, Chaetomium sp. 15003, and an unclassified Ascomycota composed 96% of the total fungal sequences in all samples. The relative abundances of these major groups were highly affected by root inoculation with F. oxysporum f. sp. radicis-cucumerinum, with a 10-fold increase in F. oxysporum sequences, but were not affected by the WR amendment. Quantitative analysis and mass-sequencing methods indicated a qualitative shift in the root's bacterial community composition in suppressive soil, rather than a change in bacterial numbers. A sharp reduction in the size and root dominance of the Massilia population in suppressive soil was accompanied by a significant increase in the relative abundance of specific populations; namely, Rhizobium, Bacillus, Paenibacillus, and Streptomyces spp. Composition of the Streptomyces community shifted significantly, as determined by PCR denaturing gradient gel electrophoresis, resulting in an increase in the dominance of a specific population in suppressive soils after only 3 days. This shift was related mainly to the increase in Streptomyces humidus, a group previously described as antagonistic to phytopathogenic fungi. Thus, suitable soil amendment resulted in a shift in the root's bacterial communities, and infection by a virulent pathogen was contained by the root microbiome, leading to a reduced disease rate.
采用田间条件下温室土壤与野生火箭（WR；Diplotaxis tenuifolia）残体混合的方法诱导对镰刀菌病的土壤抑制性。我们研究了黄瓜幼苗在接种尖孢镰刀菌根腐病菌（Fusarium oxysporum f. sp. radicis-cucumerinum）后移植到 WR 改良或非改良土壤中根系的微生物动态。接种后，非改良土壤中的病害症状在 6 天开始出现，而 WR 改良土壤则在 14 天出现。采用实时聚合酶链反应（PCR）定量根腐病菌的感染情况。接种后 3 天，WR 改良和非改良土壤中的靶标数量相似，而接种后 6 天和移植到抑制性（WR 改良）土壤中时则显著降低（66%）。这种根定植的减少与接种和移植到抑制性土壤后 21 天病害的减少（60%）有关。采用真菌内部转录间隔区基因片段的大规模测序评估黄瓜根上的真菌群落组成。与尖孢镰刀菌、Fusarium sp. 14005、Chaetomium sp. 15003 和未分类的子囊菌门相关的序列构成了所有样品中总真菌序列的 96%。这些主要群体的相对丰度受到根接种尖孢镰刀菌根腐病菌的高度影响，尖孢镰刀菌序列增加了 10 倍，但不受 WR 改良的影响。定量分析和大规模测序方法表明，抑制性土壤中细菌群落组成发生了定性变化，而不是细菌数量的变化。在抑制性土壤中，Massilia 种群的大小和根优势急剧减少，同时特定种群的相对丰度显著增加；即 Rhizobium、Bacillus、Paenibacillus 和 Streptomyces spp。PCR 变性梯度凝胶电泳（PCR denaturing gradient gel electrophoresis）测定的 Streptomyces 群落组成发生了显著变化，仅在 3 天后，抑制性土壤中特定种群的优势就增加了。这种变化主要与先前描述为拮抗植物病原菌真菌的嗜湿链霉菌（Streptomyces humidus）的增加有关。因此，适当的土壤改良导致根细菌群落发生变化，而致病病原体的感染被根微生物组所控制，从而降低了病害发生率。
