Growth promotion in chilli on inoculation with pseudomonas fluorescens and piriformosporaa

Abstract

The study entitled “Growth promotion in chilli (Capsicum annuum L.) on inoculation with Pseudomonas fluorescens and Piriformospora indica” was undertaken during 2017-2019, in the Department of Agricultural Microbiology, College of Agriculture, Vellayani, Thiruvananthapuram, with the objective to assess the compatibility of the root endophytic fungus Piriformospora indica and two Pseudomonas fluorescens strains, and to evaluate their effect on growth promotion in chilli variety Vellayani Athulya. The Pseudomonad strains used were Pseudomonas fluorescens PN026 and Pseudomonas fluorescens AMB8. Experiments comprised both in vitro and in vivo studies. For in vitro study a dual culture plate assay was done in potato dextrose agar (PDA) and coconut water agar (CWA) with the fungal and bacterial endophytes to evaluate the direct antagonism. Both Pseudomonas fluorescens PN026 and Pseudomonas fluorescens AMB8 showed antagonism to the root endophyte Piriformospora indica in PDA whereas in CWA, Pseudomonas fluorescens PN026 did not show any antagonistic effect and Pseudomonas fluorescens AMB8 showed a reduced antagonism to Piriformospora indica compaired to that in PDA. Indirect antagonism was evaluated through agar well diffusion method and paper disc diffusion method using culture filtrate of the bacterial strains and the culture filtrate from both the bacterial strains showed antagonism against Piriformospora indica in which the maximum zone of inhibition was observed in culture filtrate of Pseudomonas fluorescens AMB8. A Co-culture experiment involving P.indica and Pseudomonas strains using a single fermentation system was attempted in two different media; potato dextrose broth (PDB) and autoclaved coconut water (ACW). The flasks were incubated under agitation for 48 h and the population of the bacteria was determined at 24 h intervals by dilution plating in Kings B agar medium and it was observed that, when 10 day old cultures of the fungus in ACW and PDB were inoculated with the bacteria, ACW supported the growth of the bacteria similarly to fungus free ACW and KB medium. Co-cultivation in PDB led to a decline in bacterial population and the autoclaved coconut water can be suggested as a better medium for coculturing of P. indica and Pseudomonas fluorescens strains. A pot culture experiment was undertaken to study the effect of the different treatments on growth promotion of chilli. The experiment was laid out in CRD with six treatments and three replications and observation was taken in 15 days. The treatments comprised fungal and bacterial endophytes along with combinations of both fungal and bacterial endophytes and an uninoculated control. Different parameters like plant height, number of leaves, number of branches, number of fruits/plant, fresh fruit yield, fresh shoot weight, dry shoot weight, fresh root weight, dry root weight, days to flowering, days to fruit set and percentage root colonisation by Piriformospora indica were evaluated. Maximum plant height was recorded in the treatment with mixed inoculation of Piriformospora indica and Pseudomonas fluorescens PN026 without any significance in statistical data. A significantly increasing trend was observed in number of leaves with mixed inoculation of Piriformospora indica and Pseudomonas fluorescens PN026 from 45th day after transplanting and it was statistically on par with the treatment consisting of Piriformospora indica alone. Number of branches were found to be higher with mixed inoculation of Pirifomospora indica and Pseudomonas fluorescens PN026. There was no significant difference in the fresh weight and dry weight of shoot, whereas the fresh and dry weight of root (21.13 g and 8.26g respectively) were significantly higher in the plants treated with P. indica along with Pseudomonas fluorescens PN026. Number of fruits per plant (10.25/plant) and fresh fruit yield per plant (37.95g/plant) were recorded significantly higher with mixed inoculation of Piriformospora indica and Pseudomonas fluorescens PN026. The in vivo study disclosed that plants treated with Piriformospora indica along with Pseudomonas fluorescens PN026 were found to perform better than all other treatments. The mixed inoculation of Pseudomonas fluorescens AMB8 and P. indica had no additional advantage in plant growth in chilli. Piriformospora indica was able to successfully colonize in the plant roots applied with the bacterial endophyte. The present study revealed that plant growth promoting rhizobacteria, Pseudomonas fluorescens PN026 can be used along with Piriformospora indica, the root endophyte, for enhancing plant growth in chilli.