Rice biotechnology: Somatic hybridisation for improved salinity tolerance and xylem colonisation by rhizobia for endophytic nitrogen fixation

Abstract

At the Arles Seminar in September 1996 on Mediterranean Rice Research Activities, it was highlighted that rice is now regarded as a model plant for biotechnological developments. At this meeting on The Future of Water Management for Rice in Mediterranean Countries it is now timely to highlight studies on the somatic hybridisation of rice for improved salinity tolerance and on the xylem colonization of rice by rhizobia for endophytic nitrogen fixation. Somatic hybrid plants were obtained following the electrofusion of rice cell suspension-derived protoplasts with non-dividing leaf protoplasts of Porteresia coarctata, a saline tolerant wild species. One of the somatic hybrid plants had an allohexaploid chromosome complement and full-chromosome complements of both Oryza sativa and P. coarctata, as determined using genomic in situ hybridisation. We have also investigated whether rhizobia, whilst unable to nodulate a non-legume such as rice, might nevertheless be able to colonize the xylem of roots of rice, following entry at lateral root cracks. We have shown that extensive colonization of the xylem of both primary and lateral rice roots can be detected using rice grown under controlled conditions and inoculated with Azorhizobium caulinodans ORS571 (pXLGD4) which carries the lacZ gene and produces a blue precipitate in the presence of X-Gal. Studies are now being undertaken to determine the detailed pathway of xylem invasion following crack entry, and also to determine the possible role of xylem colonization in endophytic nitrogen fixation in rice