Effect of flavonoids on indole- acetic acid production by fast and slow growing pigeonpea Rhizobia

All the fast and slow growing rhizobial strains infecting pigeonpea (Cajanm cajan (L) Millsp.) produced indole-acetic acid (IAA) like compounds under cultural conditions. Presence of tryptophan in the culture medium enhanced the production of IAA by 2.3 folds. Crude root exudates and purified flavonoids of pigeonpea and mungbean collected at 30°C increased the IAA production in Rhizobium spp. to the extent of 80 per cent and in Bradphizobium spp. upto 9 per cent while those collected at 37°C decreased the IAA production in both the fast and slow growing rhizobia.