RHIZOSPHERE COMPETENCE OF PSEUDOMONAS SP NBRI9926 AND RHIZOBIUM SP NBRI9513 INVOLVED IN THE SUPPRESSION OF CHICKPEA (CICER-ARIETINUM L) PATHOGENIC FUNGI

In order to obtain chickpea (Cicer arietinum L.) rhizosphere-competent bacteria, 256 bacterial strains, representing different morphological types, were screened for their biocontrol activity against Fusarium o xysporum f.sp. ciceri, Rhizoctonia bataticola and Pythium sp. under in vitro conditions. Pseudomonas sp. NBRI9926 and Rhizobium sp. NBRI9513 were selected for further work because of their unique ability to inh ibit all three fungi. Spontaneous rifampicin-resistant (Rif(1)) deriva tives of Pseudomonas sp. NBRI9926 and Rhizobium sp. NBRI9513 showing a growth rate and membrane protein composition comparable to the wild-t ype were selected to elucidate their rhizosphere competence on chickpe a. Both strains showed no difference to their corresponding wild-type strains in terms of chickpea rhizosphere competence. However, when Pse udomonas sp. NBRI9926P3 was mixed in an equal or lower ratio with Rhiz obium sp. NBRI9513R7, both in sterile soil and non-sterile soil assays , Rhizobium sp. NBRZ9513R7 consistently failed to achieve titres simil ar to Pseudomonas sp. NBRI9926P3. These results suggest that antibioti c resistance-marked strains should be compared with wild-type parents before being used as monitors of parental strain survival. Pseudomonas sp. NBRI9926P3 was a better chickpea rhizosphere coloniser compared t o Rhizobium sp. NBRI9513R7. Greenhouse results demonstrated a superior biocontrol potential of Pseudomonas sp. NBRT9926P3 to control F. oxys porum f.sp. ciceri, R. bataticola and Pythium sp. compared to Rhizobiu m sp. NBRI9513R7. The screening method should prove useful in identify ing rhizosphere bacteria with the greatest potential for controlling d iseases caused by phytopathogenic fungi.