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Two cultivars of Triticum aestivum and T. turgidum were inoculated with bacteria of the genus Azospirillum in field experiments carried out in the Northern Negev and Bet Shean Valley. The results showed significant increases in yield of grain and foliage. There were significant increases in the number of fertile tillers per unit area and in the nitrogen yield. The possible mechanisms by which Azospirillum inoculation benefited wheat and other crops are discussed.

Bacteria belonging to the genus Azospirillum isolated from Cynodon dactylon roots in Israel were compared with Azospirillum brasilense from Brazil and California for their ability to fix nitrogen in association with grasses under greenhouse conditions. The plants were grown in a system which avoided cross inoculation from the inoculated soil to the control, while maintaining the natural soil microflora and humidity level in the soil close to field capacity. The organisms tested significantly increased the dry weight of Zea mays and Setaria italica leaves, the total nitrogen content of these leaves (as measured by the Kjeldahl method), and supported acetylene reduction in intact nonsterile systems as compared with the noninoculated controls. Ethylene production in intact systems could be detected after 6 h and was linear for 72 h, providing a constant soil temperature (28–32 °C) was maintained.

Free-living, dinitrogen-fixing bacteria associated with roots of grasses were isolated from several locations in Israel. Bacteria with characteristics similar to those of Azospirillum were isolated from Cynodon dactylon roots and were compared with Azospirillum brasilense from Brasil (Sp-7) and from California (Cd). Colonies of the Israeli isolates were yellow and consisted of curved rods, 0.5–0.6 μm in diameter with polar flagella, whereas colonies of A. brasilense were pink (Sp-7) and red (Cd) and the cells were 1.0–1.1 μm in diameter with polar flagella. Ultraviolet absorption spectra of soluble c and membrane-bound c and b cytochromes were similar in all isolates. When grown in semisolid agar medium with or without ammonium chloride all isolates formed a growth zone below the surface. However, they grew best under aerobic conditions in liquid medium containing NH4Cl. All isolates could use salts of malate and lactate, arabinose, and galactose, but not mannitol, as sole carbon sources; they did not need biotin to shorten their lag phase. One Israeli isolate was capable of growing and fixing nitrogen with glucose as a sole carbon source. The Israeli isolates formed aggregates above pH7.6 in liquid or semisolid medium and were capable of reducing nitrate to nitrogen gas under anaerobic conditions.