Production of Tsr factor by Rhizobium meliloti.

The root exudates of alfalfa (Medicago sativa) and mungbean (Vigna radiata) induced the Tsr (thick and short roots) factor production in Rhizobium meliloti. The factor caused a 30-40% reduction of root length in alfalfa seedlings. Pea root exudate had no Tsr induction activity. The flavonoid naringenin could replace the roots in inducing Tsr production. Naringenin-induced Tsr factor caused 70% shortening of main roots. The Tsr inducing property of naringenin was specific since quercetin and syringaldehyde had no such effect.