Can Symbiotic Nitrogen Fixation be Extended to Rice?

Abstract

The possibilities for developing new and unconventional symbiotic biological N fixation (BNF) systems for sustainable rice production are considered. Development of rice-endophytic diazotroph associations are discussed with reference to the main endophyte genera and the effect of their introduction into rice by application of the bacterial cultures on seeds prior to germination. A new procedure to ameliorate the problem of out-competition by indigenous microflora is reviewed. In consideration of development of rice-rhizobia symbioses the need to understand the limited ability of rice root exudates to induce nod gene expression in Rhizobia or Rhizobia to induce the production of nodule like structures on rice plants is recognised. The significance of observations in rice of intercellular infection of nodule like structures by Rhizobia is considered. The possibility of inducing symbiosis in rice through regeneration of rice plants from cell lines possessing amenable properties to coexist with the diazotrophs through co-culturing rice cell with a suitable diazotroph is considered. It is suggested that any BNF trait in rice would have little effect on yield at present levels.