Identification and characterization of the plant beneficial and disease suppressing fluorescent Pseudomonas sp. associated with pear by RAPD-PCR and 16S rRNA technique

The replant problem is distributed worldwide and often encountered in establishing new orchards on old sites and becoming very serious in horticultural crops. Poor growth of newly planted trees of pear is common in replanted orchards. Pseudomonas species have wide applications in agriculture as plant growth promoting and disease suppressing agents. The aim of the study was to identify and characterize the Pseudomonas sp. isolates collected from the rhizosphere of normal and replant sites of pear from different locations of Kullu, Mandi and Chamba districts using phenotypicy and genotypic characterisitcs. The 29 Pseudomonas sp. isolates were screened for the production of direct and indirect plant growth promoting activities viz., siderophores, phosphate solubilizing, HCN, ammonia, lytic enzymes, antifungal activities and plant growth regulators viz., auxins, cytokinins and gibberellins so as to select potential strains for the management of replant problem of pear. The 9 isolates were selected for the extraction and isolation of antifungal metabolite (2,4-diacetylphloroglucinol) from them which inhibits a broad spectrum of plant pathogenic fungi and control a variety of root and seedling diseases. On the basis of overall PGPR activities, 10 fluorescent Pseudomonas strains were selected for characterization by RAPD-PCR analysis. The result showed that the isolates of fluorescent Pseudomonas sp. were divided into two clusters by RAPD primers. Among all the combinations, maximum similarity (90.48%) was found between PN-7-Cha and PN-2-San isolates of Chamba and Mandi districts. However, minimum similarity (36.7%) was observed in PN-11-San and PN-7-Cha isolates of Mandi and Chamba districts. Out of 10 strains, 2 best selected isolates i.e., PN-13-San and AN-3-Cha were identified as Pseudomonas aeruginosa based on their 16S rRNA sequences.