Isolation, characterisation and in vitro evaluation of phosphorus solubilising and mineralising rhizobacterial consortia for rice (Oryza sativa L.)

Phosphorus (P) is a vital macronutrient for plant growth, however, its availability in soils is limited due to fixation and poor solubility. This limitation results in high reliance on chemical fertilisers, contributing environmental concerns such as nutrient runoff and soil degradation. This study aimed to isolate, characterise and evaluate phosphorus solubilising bacteria (PSB) and phosphorus mineralising bacteria (PMB) for plant growth promotion in rice (Oryza sativa L.) under in vitro conditions. A total of 45 distinct bacterial isolates were obtained from five different soil samples using Pikovskaya’s (TCP and DCP), phytate, lecithin and Sperber's agar media. Further, the isolates were screened for plant growth-promoting (PGP) traits such as solubilisation of phosphorus, potassium and zinc, mineralisation of phosphorus and production of siderophore, indole-3-acetic acid, ammonia and hydrogen cyanide. Compatible isolates were grouped into three consortia, designated as C1, C2 and C3. Each consortium was formulated to ensure collective expression of all the screened PGP traits. Under in vitro conditions, consortium C2 showed the highest seed germination (100%), root length (9.45 ± 0.31 cm), shoot length (6.70 ± 0.22 cm), seedling length (16.16 ± 0.52 cm) and vigour indices (I: 1616 ± 42.6; II: 5.47 ± 1.9). These values were significantly higher than those of other consortia and the control. The bacterial isolates constituting consortium C2 were identified as Bacillus sp., Priestia megaterium and Bacillus subtilis. These findings highlight the potential of C2 consortia as a sustainable bioinoculants for enhancing rice growth, thereby supporting eco-friendly and sustainable agricultural practices.