The escalating cost of chemical fertilizers, along with their prolonged usage leading to depletion of natural soil nutrients and environmental pollution, has increased the importance and demand for biofertilizers. This study aimed to evaluate the efficacy of using Azospirillum sp., Pseudomonas and mycorrhizal fungi individually and in combination for promoting nitrogen fixation, phosphate solubilization, IAA production, siderophore production, suppression of pathogenic microorganisms and enhancement of plant growth. The PGPR microorganisms, namely Azospirillum sp., Pseudomonas, and mycorrhizal fungi were isolated from the rhizosphere soil of tomato cultivation fields in Cuddalore district. AZ-5 and AZ-2, two of the isolated Azospirillum sp. strains, exhibited the highest nitrogenase activity, with values of 225.75 nmol and 210.45 nmol, respectively. AZ-5 and AZ-2 had cellular nitrogen contents of 16.95 µg/g and 15.80 µg/g, respectively, which were greater than those of the other isolates. Among the isolated Pseudomonas strains, PS-4 demonstrated the greatest phosphate solubilization activity, registering 21.75 µg P/100 mL broth. This was followed by PS-2, demonstrated significant phosphate solubilization of 18.30 µg P/100 mL broth. AZ-5,2 and PS 4,2 also exhibited enhanced production of IAA and siderophores. Among the AM fungi, particularly Gigaspora sp., showed excellent phosphate mobilization activity of 24.10 mg/kg along with 74% root colonization, indicating its efficiency as a beneficial mycorrhizal fungus. In the controlled laboratory experiment using the petri plate method, the Pseudomonas isolate effectively inhibited the growth of Fusarium oxysporum with a growth inhibition zone measuring 41.21 mm. The efficient PGPR microorganisms, specifically Pseudomonas and Azospirillum sp., recorded superior nitrogen fixation, phosphate solubilization, IAA production, and siderophore production, in conjunction with the mycorrhizal fungus Gigaspora sp., which exhibited excellent phosphate mobilization activity, were applied both individually and in combination. These microbial treatments were prepared for seven experimental treatments under pot culture conditions. At the end of the experiment, the T6 treatment performed the best, recording 21.10 cm seedling length, 94.85% seed germination, and a vigour index of 2028.7, thereby producing healthy, disease-free, and high-quality tomato seedlings. Thus, it is confirmed that the integrated application of plant growth-promoting bacteria and beneficial mycorrhizal fungi leads to the production of high-quality tomato seedlings and improved seedling yield.
Murugesan et al. (Thu,) studied this question.