The soil around plant roots is known as the rhizosphere, and it is directly impacted by soil microbes. Plant root exudation plays a crucial role in both soil fertility and plant health. Papaya rhizosphere is a very rich zone supplemented with a variety of beneficial bacteria and the soil samples were collected from this rhizosphere for the isolation of the bacterial isolates. The serial dilution of soil samples was carried out in laminar air flow to maintain aseptic conditions. The colony forming unit (CFU) count of samples ranged from 1.17 × 103 to 1.75 × 103. Isolation and purification of morphologically different bacteria were done in 60mm petri-plates. The functional activity test was carried out for purified bacteria for plant growth promoting activity such as phosphorus solubilization, potassium solubilization, siderophore production, and Indole acetic acid (IAA) production. Out of twenty bacterial isolates, 11potassium solubilizing, 6phosphorus solubilizing and 2 Siderophore producing bacterial isolates were obtained. All the isolated were capable of IAA production. Moreover, there was a positive correlation between IAA production, siderophore production, phosphorus and potassium solubilization efficiency of the bacterial isolates. Among the 11 bacterial isolates used in the treatment, PR2d isolate was found to take the minimum days taken for first seed germination (11 days), minimum days taken for 50% seed germination (21 days), per cent of seed germination (97.67 %), minimum mortality rate (4 %) and maximum IAA production (13.32 µg/mL) that promoted the growth and seed parameters of papaya plant, showing a potential use in horticulture production systems.

Papaya, seed germination, rhizosphere, PGPR

This study concludes that the bacterial isolates PR2d obtained from papaya rhizosphere were effective in early seed germination, enhancement of seed germination percentage, increased IAA production and better retention of seedlings in papaya. In order to attain sustainability, the use of bioinoculants is a novel approach that has not been utilized to its fullest potential. Production of fruits like papaya is of urgent need due to its nutritional and medicinal value and also to reduce the toxic residues of chemicals in fruits. Through this research, it can be concluded that novel isolates present in the papaya rhizosphere have great potential to improve seed germination, earliness and reduce mortality in papaya seedlings.

Jyoti Bajeli, P.N. Rai, Ranjan Srivastava, Ajay Veer Singh, Aakansha Verma and Akhilesh Negi (2023). Seed Germination Enhancement through Plant Growth Promoting Rhizobacteria (PGPR) isolated from Papaya Rhizosphere. Biological Forum – An International Journal, 15(8): 36-41.