苹果树根际促生细菌种群分析

利用选择性培养基, 对多年生苹果树根际与连作幼树根际促生细菌进行了分离和测数, 并采用BOX-PCR技术进行聚类分析。结果表明: 多年生苹果树根际细菌总量及固氮细菌、解磷细菌、硅酸盐细菌、拮抗细菌4类根际促生细菌的数量均高于连作幼树根际。在多年生苹果树根际, 硅酸盐细菌的数量最大, 解磷细菌和固氮细菌的数量次之, 拮抗细菌的数量最小; 在连作幼树根际, 解磷细菌的数量最大, 硅酸盐细菌和固氮细菌的数量次之, 拮抗细菌的数量最小。从两种土壤中获得的促生细菌分离株的BOX-PCR图谱最大的相异百分数都在1.25以上, 说明这些细菌分离株的遗传进化距离比较接近。在细菌BOX-PCR图谱相异百分数为0.25的水平上, 多年生苹果树根际促生细菌分为79个聚类群, 其中固氮细菌18个聚类群, 解磷细菌29个聚类群, 硅酸盐细菌19个聚类群, 拮抗细菌18个聚类群; 连作幼树根际促生细菌分为46个聚类群, 其中固氮细菌15个聚类群, 解磷细菌19个聚类群, 硅酸盐细菌8个聚类群, 拮抗细菌9个聚类群。多年生苹果树4类根际促生细菌的多样性、丰富度和均匀度指数均高于连作幼树根际, 而优势度指数低于连作幼树根际。与连作幼树相比, 多年生苹果树根际促生细菌具有丰富的种属多样性。

Analysis of plant growth promoting rhizobacteria population in apple rhizosphere soils

Apple replant disease (ARD) is a complex syndrome of young apple trees in replanted orchards that causes death of fine feeder roots, stunted tree growth and low yield. Analyzing changes in the number and species of plant growth promoting rhizobacteria (PGPR) in perennial apple tree (PAT) and replanted young tree (RYT) fields could lay theoretical basis for understanding the interactions among ARD and rhizosphere microbes. In this study, rhizosphere soil samples were collected in PAT and RYT fields in Changli, Hebei Province. Rhizosphere bacteria of interest in the study included azotobacter, phosphate-dissolving bacteria, potassium-dissolving bacteria and antagonistic bacteria. While rhizosphere azotobacter, phosphobacteria, potassium-bacteria were cultivated by the selective media plate cultivation method, antagonistic bacteria (with antagonistic activity against Rhizoctonia solani or Fusarium camptoceras) were isolated using the in vitro screening technique. For soil samples from both fields, microbe species and population examined by colony-forming unit (CFU) count. Also BOX Polymerase Chain Reaction (BOX-PCR) was used to fingerprint the different PGPRs. Total rhizosphere bacteria, azotobacter, phosphate-dissolving bacteria, potassium-dissolving bacteria and antagonistic bacteria were more abundant in PAT than in RYT fields. In PAT fields, potassium-dissolving bacteria were the most abundant, followed by phosphate-dissolving bacteria and then azotobacter. Antagonistic bacteria were the least abundant. In RYT fields, phosphate-dissolving bacteria were the most abundant, followed by potassium-dissolving bacteria and then azotobacter. Antagonistic bacteria were also the least abundant. Based on BOX-PCR fingerprints cluster analysis of PGPR, there were over 1.25 dissimilarities in both PAT and RYT fields. This somehow suggested close genetic evolutionary distance among the isolates. PGPR in PAT fields were divided into 79 clusters; including 18 azotobacter, 29 phosphate-dissolving bacteria, 19 potassium-dissolving bacteria and 18 antagonistic bacteria clusters at 0.25 BOX-PCR fingerprint dissimilarity. Similarly, PGPR in RYT fields were divided into 46 clusters; including 15 azotobacter, 19 phosphate-dissolving bacteria, 8 potassium-dissolving bacteria and 9 antagonistic bacteria clusters at 0.25 BOX-PCR fingerprint dissimilarity. Replanting therefore significantly influenced rhizosphere bacteria abundance in orchard fields. Higher PGPR population and biodiversity were noted in PAT than in RYT fields. While the indices of diversity, richness and evenness of azotobacter, phosphate-dissolving bacteria, potassium-dissolving bacteria and antagonistic bacteria were higher in PAT than in RYT fields, the reverse was true for dominance index. Based on the findings, abundant microbes existed in PAT fields and with complex and stable ecological distribution of microbial community. However, only less PGPR with great vitality colonized RYT fields and with simple rhizosphere microbial community structures.