Physiological and biochemical effects of Methylobacterium sp. strains and foliar-applied methanol on growth and development of rice Oryza sativa L.

摘要

Phylloplane saprophytic microflora and epiphytic microorganisms during their vital life sustaining activities secrete biologically active substances that directly or indirectly influence the biochemical and physiological processes of host plant tissue. Although these compounds are likely to be in micro-concentrations they could have significant beneficial or detrimental effects on growth and metabolic processes of the host plant.; This study was designed to evaluate the effect of some Methylobacterium sp. strains on growth and development of rice at three levels, tissue culture, seedlings in vitro and in mature plants grown in simulated natural conditions in a greenhouse. The experiments were carried out to evaluate the promise of several Pink-pigmented facultative methylotrophic bacteria (PPFM) strains potential as phylloplane microbial factors that could significantly increase growth, development and absolute rice grain yield. As a follow up study, in vitro experiments were carried out to determine if the observed growth stimulatory effect resulting from foliar methanol treatment was partly mediated by some of the PPFM strains such as the Q5, originally isolated from rice leaf.; Data and findings were analyzed qualitatively and quantitatively using descriptive statistics, Pearson's correlation, Students t-test and analysis of variance (ANOVA). Qualitative findings revealed that there is a wide range of facultative methylotrophic bacteria strains on the leaf surface of rice plants. Inoculation of two isolated Methylobacterium sp. strains designated Q4 and Q5 onto seed embryo-derived calli significantly stimulated cell proliferation and differentiation in tissue culture. Inoculation of either the Q4 or Q5 strain on 9 day old axenic rice seedlings significantly increased seedling growth in height, leaf development, root growth and biomass in vitro. Qualitative evidence derived from tissue culture experiments indicated that the Q4 and Q5 strains plant growth and development stimulatory properties were mediated by microbial derived cytokinin and auxin-like growth regulators.; Evaluation of the physiological effects of foliar-applied aqueous methanol revealed that the stimulatory effect of methanol is partly mediated by methylotrophic bacteria on rice leaf surface. Significant increases in leaf chlorophyll content and biomass accumulation in tropical and temperate rice cultivars were observed in treated plants. However the response was not cultivar specific. Indirect evidence from in vitro experiments showed that rice plants and their PPFM strains such as Q4 and Q5 constitute a group of mutualistic cobionts. The physiological partnership appeared to be based on production and release of methanol from plants tissues in microquantities, and the utilization of plant-derived methanol as source of carbon by PPFM including Q4 and Q5.; Taxonomic characterization of the Q4 and Q5 based on morphological characteristics, carbon-compound utilization properties, resulted in identification and placement of the two strains in the 7 and 35e strain category in the genus Methylobacterium sp. The findings from the in vitro and glasshouse experiments have shown that the inoculation of rice plants in the field with either Q4 or Q5 PPFM strain via seed coating technique, coupled with application of methanol treatments on rice foliage is a viable alternate technology that could significantly increase rice production.