Evaluation of fluorescent Pseudomonas spp. with single and multiple PGPR traits for plant growth promotion of sorghum in combination with AM fungi

Traits involved in plant growth promotion by bacteria are ambiguously decided as phytohormones, siderophores, HCN, proteases, chitinases, cellulases, ammonia, exopolysaccharide production and phosphate solubilization or antagonistic activity. A total of 40 fluorescent Pseudomonas strains were isolated from diverse soils of various agro-ecosystems of India. Among these 7 strains viz , P1, P10, P13, P18, P21, P28 and P38 were selected depending on their character of possessing single or multiple PGPR traits. These isolates individually and in combination with AM fungi ( Glomus fasciculatum and Glomus aggregatum ) were used for treating sorghum seeds. 25 days after sowing, plants were analysed for different plant growth promoting parameters. It was observed that strains in presence of mycorrhizae performed well compared to the strains devoid of mycorrhizae. Pseudomonas sp. P1 possessing GA3, EPS production and ‘P’ solubilization performed well. Pseudomonas sp. P38 which was a volatile (HCN) producer but a good phosphate solubilizer did not perform well. Strain P28 with multiple PGPR traits did not show the expected out come. Results varied when mycorrhizae was used in combination. P10 and P13 which were good in IAA, GA3, EPS, siderophore and ‘P’ solubilization performed well with mycorrhizae, with an overall increase in plant biomass, leaf area, total chlorophyll and mycorrhizal infection compared to other combinations. Here, strain P1 in combination with mycorrhizae did not show significant increase in plant growth compared to P10 and P13. Hence, mere possession of multiple PGPR traits does not confer fluorescent Pseudomonas strains as PGPR. Further studies have to be carried out in order to evaluate the other traits which may be involved in plant growth promotion.