Efficacy of peat-based bioformulation of microbial co-inoculants with silicon for growth promotion of rubber plants

Recently, microbial consortia of rhizobacteria and arbuscular mycorrhizal fungi (AMF) had demonstrated the potential as plant growth promoting microbes in sustainable agriculture. This study aimed to investigate the effect of a peat moss-based formulation of Enterobacter sp. UPMSSB7, Glomus mosseae, and silicon (Si) on the survival of microbial inoculants under storage conditions for 24 weeks. The study further assessed the potential of this bioformulation to promote the growth of rubber plants in a glasshouse trial. The Enterobacter sp. UPMSSB7 isolated from rubber tree's rhizosphere, can solubilize silicates and has plant growth promoting properties. G. mosseae is an AMF, having symbiotic relationship with majority of cultivated crops. The application of Si has emerged as a sustainable strategy for crop health. It improves soil fertility through nutrient maintenance and also alleviates various biotic and abiotic stresses. Results from laboratory test revealed that bioformulation of co-inoculants with Si sustained a high survivability of Enterobacter sp. (18 × 108 CFU g-1) and G. mosseae (35 spores per 10 g) in formulation for up to 24 weeks of storage. Results from the glasshouse experiment revealed that 24 weeks after treatment with bioformulation of co-inoculants with Si increased the stem height, girth, leaf area, dry weight of shoot and root, chlorophyll content, microbial population of Enterobacter sp. (1.4 × 108 CFU g-1 soil) and G. mosseae (78 spores/10 g soil) in rhizosphere and also increased N, P, K and Si contents in rubber seedlings than bioformulation of single inoculant with Si and control. Our findings indicate that peat moss-based formulation of co-inoculants Enterobacter sp. UPMSSB7 and G. mosseae added with Si proved to be the most effective. This formulation not only maintained good microbial survivability but also significantly enhanced the rubber plants growth compared to the bioformulation of single inoculants. This promising approach using a peat moss-based formulation of microbial co-inoculants with Si, could be further explored for growth enhancement of rubber trees under field conditions.