Endophytic establishment of Azorhizobium caulinodans in wheat

Abstract

SUMMARYNitrogen fixing nodules are formed on the roots and stems of the tropical legume Sesbania rostrata by A orhi obium caulinodans as a result of crack entry invasion of emerging lateral roots. Advantage was taken of this invasion capability of A. caulinodans to determine whether inoculation of the non-legume wheat with A. caulinodans would result in the endophytic establishment of azorhizobia within wheat roots. Advantage was also taken of the oxygen tolerance of the nitrogenase of free-living azorhizobia to assess the extent to which the endophytic establishment of azorhizobia in wheat roots would provide a niche for nitrogen fixation of benefit to the plant. Wheat was inoculated with A. caulinodans and grown in pots under controlled conditions, without added growth regulators and without addition of fixed nitrogen. Microscopic examination of the short lateral roots of inoculated wheat showed invasion of azorhizobia between cells of the cortex, within the xylem and the root meristem. Acetylene reduction assays combined with analysis of tissue nitrogen levels indicated the likelihood that colonization led to nitrogenase activity. Inoculated wheat showed significant increases in dry weight and nitrogen content as compared with uninoculated controls. We discuss the extent to which this nitrogen fixation is likely to involve symbiotic nitrogen fixation, and we indicate the need for field trials to determine the extent to which inoculation of wheat with A. caulinodans will reduce the requirement for inputs of nitrogenous fertilizers.

Expressed nifH Genes of Endophytic Bacteria Detected in Field-Grown Sweet Potatoes (Ipomoea batatas L.)

“…N 2 -fixing activities have been found only when carbohydrates such as sucrose 7) , malate 15,39) and citrate 31) were fed to the plant. In the present experiment, the expression of the nifH gene was detected in August, two months after planting (Table 2), but was rarely detected in October.…”

The Role of Soil Beneficial Bacteria in Wheat Production: A Review

“…Wheat (Triticum aestivum L.) [142] Salinity Azospirillum sp Durum wheat (Triticum durum) [128] [207] Azorhizobium caulinodans Wheat N2 fixation Dry weight, nitrogen content [192] Azotobacter chroococcum Wheat Rhizospheric P solubilization, N2 fixation, IAA Seed emergence radicle and plumule length [114] Azotobacter sp.…”

“…Experiments as field trials with dry land areas, the co-inoculations of PGPR strains for wheat, maize and barley with chemical fertilizers gave improved response [3,183,[192][193][194][195][196][197]. [24] Döbereiner J, editor Biological N2 fixation by endophytic diazotrophs in non-leguminous crops in the tropics.…”

Xylem colonization of the legume Sesbania rostrata by Azorhizobium caulinodans

“…inoculated with ORS571, and Sesbania rostrata inoculated with ORS571, ORS604 or ORS611, show that lateral root xylem elements of S. rostrata are colonized after invasion from the rhizoplane, but only by the natural symbiont that also nodulates the plant. However, xylem colonization has been observed in wheat which does not develop nodules; plants were pot-grown and inoculated repeatedly with Azorhizobium caulinodans (Sabry et al 1997). Therefore, under some growth conditions, A. caulinodans ORS571 may be able to colonize the xylem of plants other than S. rostrata.…”

“…Inoculation of S. rostrata with Azorhizobium caulinodans ORS571 (Dreyfus et al 1988) results in production of nodules on roots (Ndoye et al 1994) and stems (Tsien et al 1983). Interestingly, ORS571 is able to establish itself endophytically in the roots of rice (Christiansen-Weniger 1996) and wheat (Sabry et al 1997), although these plants are not natural hosts and nodules do not develop.…”