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Inoculation experiments of natural pastures with the rhizobacterium Azospirillum brasilense were conducted in Israel in 1996, in two climatically di †erentiated regions. T hese experiments were carried out as part of a project with the objective of estimating the potential of the inoculation technique in improving pasture yields. T he e †ects of inoculation with A. brasilense were compared to P ± fertilization and to untreated controls. In two semiarid sites, it was generally observed that both the inoculation and the P ± fertilization treatments increased pasture yield as measured by dry weight biomass. It was also found that both inoculation and P ± fertilization treatments caused an enrichment in legumes relatively to grasses and forbs. Despite the ecological complexity of these sites and the variability of the data, statistical signiÐcance was generally achieved. In a more topographically uniform site, located in a typical Mediterranean climate, the positive e †ects of A. brasilense inoculation in plant ± growth were substantially clear, with Ðnal yields duplicated in both inocu ± lation and combined (inoculation and P ± fertilization) treatments in comparison to P ± fertilization alone and untreated controls. T he potential of using A. brasilense for growth promotion of natural pastures is discussed.

In a 50-L pot experiment with Medicago sativa grown under nonsterile conditions, a combined treatment of Azospirillum and Rhizobium was measured against soil inoculated with Rhizobium or Azospirillum alone or a control with a low background level of autochthonous rhizobia. The combined treatment significantly increased the shoot length and weight at 6 weeks and the regrowth shoot weight at 14 weeks when compared with the treatment with Rhizobium alone. In 1.5-L pots in which gnotobiotic conditions were maintained, the combined treatment led to more nodules on the main root at intermediate Rhizobium concentrations, and a greater root surface area at intermediate and high Rhizobium concentrations after 2 weeks but not after 4 weeks. In pouch-grown seedlings, plants were inoculated with either Rhizobium alone or in combination with Azospirillum or applied together with a flavonoid, luteolin (a nodulation gene inducer), or with a cytokinin, benzyl adenine. Luteolin had similar effects to those of Azospirillum in increasing the main root nodule number and the total nodule number. With Fahraeus slides, a significant increase was observed in the number of root hairs and the root diameter in the presence of Azospirillum as compared with the control and Rhizobium alone. There was no increase in the total number of infection threads; however, the combined treatment caused a significant decrease in the percentage of infected root hairs.Key words: Rhizobium, Azospirillum, Medicago, flavonoid, inoculation.

The considerable industrial interest in the qualitative and quantitative production of polyhydroxyalkanoates in microorganisms has led to the characterization of those synthesized in the nitrogen-fixing bacteria Azospirillum brasilense and Azotobacter paspali. In contrast to some other bacterial species, Azospirillum brasilense does not produce copolymers of hydroxyalkanoates when grown under the different carbon sources assayed, namely n-alkanoic acids, hydroxyalkanoates, and sugars with varying C:N ratios. Rather, only homopolymers of polyhydroxybutyrate were detected, comprising up to 70% of the cell dry mass. No copolymers were detected in Azotobacter paspali. Quantitative analyses of poly(β-hydroxybutyrate) are also presented.Key words: Azospirillum spp., Azotobacter paspali, polyhydroxyalkanoate analysis, PHA, PHB.

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