Inoculation with Azospirillum Increased Exudation of Rhizobial nod-Gene Inducers by Alfalfa Roots. Hanne Volpin. Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel. Saul Burdman (1), Susana Castro-Sowinski (2), Yoram Kapulnik (3), Yaacov Okon (1). (1) Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel; (2) lnstituto Clemente Estable, Montevideo, Uruguay; (3) Institute of Field and Garden Crops, ARO, The Volcani Center, Bet Dagan 50250, Israel. MPMI 9:388-394. Accepted 19 February 1996. Copyright 1996 The American Phytopathological Society.

Azospirillum brasilense caused a significant increase in the nod-gene inducing activity of crude alfalfa root exudates when compared to exudates of the noninoculated controls. nod-gene inducing activity of exudales from yeast extract-elicited roots was also increased, but to a lesser extent. Fractions separated by HPLC from the exudates of roots treated with Azospirillum, yeast extract, and a control showed different nod-gene inducing capacities. The profiles of flavonoids extracted from the Azospirillum-inoculated roots differed from those of controls, but the difference was less pronounced than was seen in the exudates. The profile of the flavonoids from elicited roots differed greatly from the former two. The data obtained from the flavonoid analyses were in accordance with enzyme activities and mRNA levels of the defense-related proteins phenylalanine ammonia-lyase (PAL), chalcone isomerase (CHI), and isoflavone reductase (IFR); CHI activity and its mRNA were induced in the roots elicited by yeast extract, whereas the activities of PAL and CHI, and mRNA levels of PAL, CHI, and IFR were not induced by Azospirillum.