Background: This study assessed the effect of different sticking agents viz., gum arabic, guar gum and xanthan gum for coating Rhizobium sp. and Arbuscular Mycorrhizal Fungi (AMF) on seed germination and vigour of blackgram seeds. Methods: The surface sterilised seeds were first coated with different sticking agents as per the following treatments, T0 - Dry seed, T1 - Water, T2 - Gum arabic 20% w/v, T3 - Guar gum 0.5% w/v, T4 - Xanthan gum 0.3% w/v followed by coating with Rhizobium sp. and AMF liquid cultures. Result: Among the different sticking agents, gum arabic (20%) when used as a sticker for coating Rhizobium sp. and AMF, increased the seed germination (95%) and vigour index (21.85) of blackgram compared to the control. The efficacy of inoculation depended on the survival of inoculants on seeds. On using sticking agents, the survival of microbes could be extended up to 48 h of treatment and 87 per cent AMF colonization with gum arabic (20%) as deduced from the viability studies.

Background: Blackgram (Vigna mungo (L.) Hepper) belonging to the Leguminoceae family is rich in protein. In this crop, biological seed treatment is an environmentally sound approach for improving the vigour of seeds. Besides legume-Rhizobium symbiosis, several other beneficial microbes play a crucial role in vigour enhancement in blackgram. Methods: The surface sterilised seeds were first coated with 20% gum acacia followed by the coating with bioinoculants viz., T0 - Control (Dry seed), T1 - Rhizobium sp. BMBS + Arbuscular Mycorrhizal Fungi (AMF) + Methylobacterium extorquens AM1 and T2 - Rhizobium sp. BMBS + AMF + Bacillus velezensis. Result: Inoculation of blackgram seeds with the Rhizobium sp. BMBS and AMF with Methylobacterium extorquens AM1 resulted in a significant increase in germination (97%), dry matter production (0.237 g 10 seedlings-1), vigour index (22.99) and seed mobilization efficiency (1.11) as compared to control seeds. The biochemical parameters such as á-amylase and proteases were found to be significantly higher in the Rhizobium sp. BMBS + AMF + Methylobacterium extorquens AM1 inoculated seeds. Changes in root exudates composition due to co-inoculation assessed through GC-MS, indicated compounds with antioxidant and antimicrobial activities. Our results confirmed that the positive interaction of rhizobial strain BMBS and AMF with Methylobacterium extorquens AM1 may emerge as a novel bio-inoculant for sustainable pulse productivity.