Raaijmakers J M, Weller D M
Root Disease and Biological Control Research Unit, USDA-ARS, Washington State University, Pullman, Washington 99164-6430, USA. jos.raaijmakers@
Appl Environ Microbiol. 2001 Jun;67(6):2545-54. doi: 10.1128/AEM.67.6.2545-2554.2001.
The genotypic diversity that occurs in natural populations of antagonistic microorganisms provides an enormous resource for improving biological control of plant diseases. In this study, we determined the diversity of indigenous 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. occurring on roots of wheat grown in a soil naturally suppressive to take-all disease of wheat. Among 101 isolates, 16 different groups were identified by random amplified polymorphic DNA (RAPD) analysis. One RAPD group made up 50% of the total population of DAPG-producing Pseudomonas spp. Both short- and long-term studies indicated that this dominant genotype, exemplified by P. fluorescens Q8r1-96, is highly adapted to the wheat rhizosphere. Q8r1-96 requires a much lower dose (only 10 to 100 CFU seed(-1) or soil(-1)) to establish high rhizosphere population densities (10(7) CFU g of root(-1)) than Q2-87 and 1M1-96, two genotypically different, DAPG-producing P. fluorescens strains. Q8r1-96 maintained a rhizosphere population density of approximately 10(5) CFU g of root(-1) after eight successive growth cycles of wheat in three different, raw virgin soils, whereas populations of Q2-87 and 1M1-96 dropped relatively quickly after five cycles and were not detectable after seven cycles. In short-term studies, strains Q8r1-96, Q2-87, and 1M1-96 did not differ in their ability to suppress take-all. After eight successive growth cycles, however, Q8r1-96 still provided control of take-all to the same level as obtained in the take-all suppressive soil, whereas Q2-87 and 1M1-96 gave no control anymore. Biochemical analyses indicated that the superior rhizosphere competence of Q8r1-96 is not related to in situ DAPG production levels. We postulate that certain rhizobacterial genotypes have evolved a preference for colonization of specific crops. By exploiting diversity of antagonistic rhizobacteria that share a common trait, biological control can be improved significantly.
拮抗微生物自然种群中出现的基因型多样性为改善植物病害的生物防治提供了巨大资源。在本研究中，我们测定了在对小麦全蚀病具有天然抑制作用的土壤中生长的小麦根际土著2,4 - 二乙酰基间苯三酚（DAPG）产生菌假单胞菌属的多样性。在101个分离株中，通过随机扩增多态性DNA（RAPD）分析鉴定出16个不同的组。一个RAPD组占DAPG产生菌假单胞菌属总群体的50%。短期和长期研究均表明，以荧光假单胞菌Q8r1 - 96为例的这种优势基因型高度适应小麦根际。与基因型不同的另外两个DAPG产生菌荧光假单胞菌菌株Q2 - 87和1M1 - 96相比，Q8r1 - 96建立高根际种群密度（10⁷ CFU g根⁻¹）所需的剂量要低得多（仅10至100 CFU种子⁻¹或土壤⁻¹）。在三种不同的原始生土中，经过八次连续的小麦生长周期后，Q8r1 - 96的根际种群密度维持在约10⁵ CFU g根⁻¹，而Q2 - 87和1M1 - 96的种群在五次周期后相对迅速下降，在七次周期后无法检测到。在短期研究中，菌株Q8r1 - 96、Q2 - 87和1M1 - 96在抑制全蚀病的能力上没有差异。然而，经过八次连续生长周期后，Q8r1 - 96仍能将全蚀病控制在与全蚀病抑制性土壤中相同的水平，而Q2 - 87和1M1 - 96则不再具有防治效果。生化分析表明，Q8r1 - 96优越的根际竞争力与原位DAPG产生水平无关。我们推测某些根际细菌基因型已经进化出对特定作物定殖的偏好。通过利用具有共同特性的拮抗根际细菌的多样性，可以显著改善生物防治效果。
