Effect of Rhizophagus spp. and plant growth-promoting Acinetobacter junii on Solanum lycopersicum and Capsicum annuum T. Padmavathi • R. Dikshit • S. Seshagiri Received: 17 September 2014 / Accepted: 13 February 2015 Ó Botanical Society of Sao Paulo 2015 Abstract Beneficial interactions of plant growth-pro- moting rhizobacteria and arbuscular mycorrhizal fungi (AM Fungi) are vital to keep agriculture sustainable. The present study involves the isolation of Acinetobacter junii and the extraction of spores of Rhizophagus intraradices and R. fasciculatus from the rhizospheric region of Solanum lycopersicum and Capsicum annuum plants. Dual inocula- tion resulted in growth promotional aspects such as on the fruit yield (1.98 kg plant -1 ), increased biomass (30.36 g tomato; 10.67 g bell pepper), %93 % root colonization, phosphate accumulation in shoots (2.06 mg mL -1 tomato; 2.26 mg mL -1 bell pepper), number of spores (238 tomato, 242 bell pepper), and glomalin, a soil-related protein (16.75 mg mL -1 tomato; 18.09 mg mL -1 bell pepper) in both the plants. Keywords Acinetobacter junii Á Glomalin Á PGPR Á Rhizophagus fasciculatus Á Rhizophagus intraradices Á Rock phosphate Introduction Plant growth is influenced by several abiotic and biotic factors. The skinny layer of soil surrounding plant roots is termed as rhizosphere which is an enormously vital and active area for root activities and metabolism. The mi- croorganisms such as fungi, bacteria, and algae co-exist in the rhizosphere, and these active microbial populations are known to wield constructive effects on plant growth. Plant growth-promoting rhizobacteria (PGPR) augment plant growth by nitrogen fixation from atmospheric, solubiliza- tion of phosphate, creation of siderophores, and synthesis of plant growth-promoting hormones, e.g., gibberellic acid, indole acetic acid, and cytokinin (Sivasakthi et al. 2014). One of the most important beneficial effects of PGPR is their interaction with AM fungi. Linderman (1997) re- ported a robust stimulatory effect on growth and develop- ment of AM fungi with PGPR, whereas Azco ´n (1987) had reported increased mycelial growth of Funneliformis mosseae due to unidentified PGPR. These reports suggest that formation and function of Arbuscular mycorrhizal (AM) fungi could be optimized by the co-inoculation of selected PGPR and AM fungi. AM fungi are symbiotic organisms that commonly occur in roots of plants. It generally benefits plant growth because of its ability to increase the supply of nutrients, including phosphorus, at levels several times more than non-mycor- rhizal plants to host plants (Koide and Schreiner 1992). AM fungi increase root surface area for absorption of water and nutrients and improve higher branching of plant roots (Roger 2008). The mycorrhizal hyphae extend from plant roots to the soil, enabling the roots to increase contact with a greater soil area. AM fungi also increase drought resis- tance in plants and plant defense against pathogens (Garg and Chandel 2010). Tomato (Solanum lycopersicum L.) and bell pepper (Capsicum annuum L.) are rich in vitamin A, C, and E that have antioxidant properties. N, P, K, Mg, and Ca are required by crops in the right quantity and at the right time for good production and yield (Olaniyi and Ajibola 2008). T. Padmavathi (&) Á R. Dikshit Department of Microbiology, Centre of PG Studies, Jain University, 18/3, 9th Main road, Jayanagar 3rd Block, Bangalore 560011, Karnataka, India e-mail: vam2010tpraviju@gmail.com; blrsn@rediffmail.com S. Seshagiri Centre for Emerging Technologies, Jain Global Campus, Jakkasandra Post, Ramanagara District, India 123 Braz. J. Bot DOI 10.1007/s40415-015-0144-z