Isolation and screening of rhizobia for auxin biosynthesis and growth promotion of mung bean (Vigna radiata L.) seedlings under axenic conditions

A series of screening experiments to evaluate the effectiveness of rhizobia for producing auxins and improve growth and nodulation of mungbean (Vigna radiata L.) were carried out under axenic conditions. Forty four iolatess of rhizobia were isolated using standard procedures. Auxin biosynthesis by these rhizobial isolates was determined in the absence and presence of L-Trp, a physiological precursor of auxins. Rhizobial isolates varied widely in auxins biosynthesis capabilities. On the basis of auxins biosynthesis, a pouch experiment was conducted for screening thirty four efficient isolates of rhizobia for the growth promotion of mung bean. Results of pouch study showed that inoculation with selected rhizobial isolates increased the root /shoot length, fresh, and dry shoot weight of mung bean up to 33, 59, 71, 148, 107 and 188%, respectively, over untreated control. Further studies are needed under glasshouse and field conditions for confirmation of these results.