Relationship between Indole Acetic Acid Production by Fluorescent Pseudomonas and Plant Growth Promotion
Forty fluorescent pseudomonads were quantitatively evaluated for indole acetic acid (IAA) producing ability in the presence (trypt+) or absence (trypt-) of tryptophan and growth promotion in groundnut in response to seed treatment with high IAA producers was analyzed. There were significant differences in the amounts of IAA produced by the isolates and more amounts of IAA were released in trypt+. In trypt- increased IAA production was noticed for up to 144h and thereafter it stabilized or decreased. Analysis of plant growth promotion showed that the maximum root length (187.5mm) was exhibited by plants treated with BA16(A)2 which was a medium IAA producer whereas the highest IAA producer BA1(E)2 (32.2 Î¼g/ml of IAA) showed a root length of 167.3mm. The isolate OTN7(E)2 which was a low IAA producer showed good root lengths of 148.3mm (sterile soil) and 133.3mm (unsterile soil). When the shoot lengths were compared, highest shoot length of 213.3mm (sterile soil) was by BA4(D) which is a medium to high IAA producer and in unsterile soil highest shoot length of 198.67mm was shown by the isolate ND1which is also a medium to high IAA producer. The highest IAA producer BA1(E)2 showed a low shoot length of 156.7mm (sterile soil) and 115mm (unsterile soil). The results in some way do establish that plant growth is not directly influenced by high IAA producers. Root growth seemed to be more affected by high IAA producers in unsterile soil and maximum vigour index of 32600 was exhibited by BA2(D)1 which is a medium IAA producer and the minimum of 15750 was by BA1(E)2 which is a high IAA producer. Hence IAA producers of the fluorescent Pseudomonas group showed significant plant growth when compared with control but plant growth was not greatly influenced by those organisms that produced high amounts of IAA. Antagonistic Pseudomonas spp. able to release moderate or even low amounts of IAA may be better growth promoters.
Pseudomonas, Indole Acetic Acid, Shoot Length, Root Length, Plant Growth Promotion, Tryptophan, Vigour Index.
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