DEVELOPMENT OF A STRAIN-SPECIFIC PROBE TO FOLLOW INOCULATED AZOSPIRILLUM-LIPOFERUM CRT1 UNDER FIELD CONDITIONS AND ENHANCEMENT OF MAIZE ROOT DEVELOPMENT BY INOCULATION

In order to develop a reliable and specific tool for the detection of Azospirillum lipoferum CRT1, randomly cloned DNA fragments from this s train were used as hybridization probes to differentiate A. lipoferum CRT1 from 29 closely related Azospirillum strains. Two cloned fragment s hybridizing only with DNA from A. lipoferum CRT1 (CRT1-5 and CRT1-7) were considered as specific probes of this strain. CRT1-7 fragment (1 .4 kb) was further tested for purity control of the inoculant Azogreen -m by colony hybridization. The sequence of the CRT1-7 fragment has be en determined and compared with those present in databases: no signifi cant similarity with other sequences was detected. This probe permitte d us to count specifically A. lipoferum CRT1 cells on maize roots duri ng a field trial. During the first two weeks, A. lipoferum CRT1 remain ed at 10(7) CFU plant-l. Afterwards, bacterial concentration sharply d ecreased. We could not detect any CRT1 cells on maize roots 28 days af ter sowing. Concurrently, three plant parameters were estimated (plant height, primary root length and root fresh weight). The results showe d that A. lipoferum CRT1 growth promotion effect began early on (from day 14) in plant development and increased in spite of a rapid decreas e of bacterial density. (C) 1998 Federation of European Microbiologica l Societies. Published by Elsevier Science B.V. All rights reserved.