Maliti, C. M. (Department of Biology & Med. Lab. Technology, Bronx Comm. College, CUNY, University Avenue & West 181 Street, Bronx, NY 10453), D. V. Basile (Department of Biological Sciences, Lehman College, CUNY, Bronx, NY 10468), and W. A. Corpe (Department of Biological Sciences, Columbia University, New York, NY 10027). Effects of methylobacterium spp. strains on rice Oryza sativa callus induction, plantlet regeneration and seedlings growth in vitro. J. Torrey Bot. Soc. 132: 355–367. 2005.—Leaf surfaces of higher plants are colonized by diverse microorganisms. In the present study we report the isolation two strains of pink-pigmented methylotrophic bacteria (PPFM) designated Q4 & Q5. Both strains significantly stimulated growth and development of two rice cultivars, Japonica cv. CR76 and Indica cv. A301, cultured axenically on MS or B5 medium. Co-incubation of strains Q4 and Q5 with embryo-derived rice calli on B5 medium-devoid of exogenous phytohormones resulted in continued callus growth but inhibited plantlet regeneration. These results mimicked those produced by B5 medium supplemented with auxin and cytokinin. Co-culture of Q4 & Q5 as cobionts with 5 day old Japonica and Indica seedlings resulted in a significant (P ≤ 0.05) stimulation of four growth parameters; root development, stem growth, leaf development and biomass productivity, measured in 9 day growth period. The results of the in vitro experiments indicate that strain Q4 and /or Q5 inhabiting rice plant surfaces under cultivation could significantly stimulate the plants growth and development.