Functional characterization of Pseudomonas and actinobacteria isolates and their role in growth promotion and tomato leaf curl virus disease control

Abstract

Thirty Pseudomonas isolates and five actinobacteria were tested for their ability to solubilize mineral insoluble phosphate sources, potential to fix atmospheric nitrogen, siderophore production and hormone synthesis, which are characteristic properties of plant growth promoting rhizobacteria (PGPR). Sixteen isolates could solubilize mineral phosphate among which eight isolates of Pseudomonas showed the property of acidification of broth. Eighteen Pseudomonas isolates and four isolates of actinobacteria grew on N-free media indicating potential to fix atmospheric nitrogen. Nine Pseudomonas and two actinobacteria isolates produced siderophore, whereas the hormone production was observed in all isolates. The level of indole acetic acid production was highest in AUDT143 (52 μg ml-1) followed by 360 (2) (28.87 μg ml-1). Gibberellin production was noticed in all isolates, which ranged from 7 to 80 μg ml-1 of culture filtrate. The eight isolates, Pseudomonas AUDP326 (4), AUDP360 (2), AUDP139, AUDPB40 and AUDP218 (1) and the actinobacteria AUDT217, AUDT152 and AUDT143 could significantly promote the plant growth parameters like shoot length, root length, root dry weight, shoot dry weight and chlorophyll content in tomato and five isolates Pseudomonas AUDP326 (4), AUDP360 (2), AUDP139 and actinobacteria AUDT217 and AUDT152 were effective against tomato leaf curl virus disease.