THE IMPAIRMENT OF THE NODULATION PROCESS, INDUCED BY A BRADYRHIZOBIUM-JAPONICUM EXOPOLYSACCHARIDE MUTANT IS DETERMINED BY THE GENOTYPE OF THE HOST-PLANT

The deletion mutant Bradyrhizobium japonicum Delta P22 produces a stru cturally altered exo-polysaccharide. The nodulation of two cultivars e ach of Glycine max and Glycine soja, and cultivars of Macroptilium atr opurpureum and Vigna radiata, infected with this mutant was examined i n order to analyze the role of the exopolysaccharide in the infection process of plants with a determined nodule type. All host plants analy zed exhibited delayed nodulation and formed fewer nodules per plant. M orphological studies confirmed these results. In V. radiata later step s in nodule development proceeded without further disturbances, wherea s with G. soja PI407287 minor changes were detected. In contrast, the inoculation of Gl. soja PI468397 and M. atropurpureum lead to the form ation of nodules most of which were not infected by Bradyrhizobium jap onicum Delta P22 (inf(-)). However, on M. atropurpureum at least some effective nitrogen-fixing nodules developed. Such nodules did not emer ge from G. soja PI468397. Inf(-) nodules were arrested in an early sta ge of nodule development, and symptoms of plant defense responses were observed.