| The Biocontrol Activity of Chromobacterium sp. Strain C-61 against Rhizoctonia solani Depends on the Productive Ability of Chitinase |
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Seur Kee Park, Myung Chul Lee, Gary E. Harman |
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| Abstract |
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A chitinolytic bacterium, Chromobacterium sp. strain C-61, was found strongly antagonistic to Rhizoctonia solani, a causal agent of damping-off of eggplant. In this study, the biocontrol activity and enzymatic characteristics of strain C-61 were compared with its four Tn5 insertion mutants (C61-A, -B, -C, and -D) that had lower chitinolytic ability. The chitinase activity of a 2-day old culture was about 76%, 49% and 6% level in C61-A, C61-B and in C61-C, respectively, compared with that of strain C-61. The β-N-acetylhexosaminidase (Nahase) activity was little detected in strain C-61 but increased largely in C-61A, C61-B and C61-C.Activities of chitinase and Nahase appeared to be negatively correlated in these strains. Another mutant, C-61D, produced no detectable extracellular chitinase and Nahase. The in vitro and in vivo biocontrol activities of strain C-61 and its mutants were closely related to their ability to produce chitinase but not Nahase. No significant differences in population densities between strain C-61 and its mutants were observed in soil around eggplant roots. The results of SDS-PAGE and isoelectrofocusing showed that a major chitinase of strain C-61 is 54-kDa with pI of approximately 8.5. This study provides evidence that the biocontrol activity of Chromobacterium sp. strain C-61 against Rhizoctonia solani depends on the ability to produce chitinase with molecular weight of 54-kDa and pI of 8.5. |
| Key Words:
biocontrol activity, chitinase, Chromobacterium sp., damping-off, eggplant, Rhizoctonia solani, Tn5 insertion mutants |
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