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In this research, antibiotic-resistant mutants of antagonistic
bacteria to rifampicin (Rif) and nalidixic acid (Nal) were developed via
spontaneous mutation and their effectiveness in controlling cotton seedling
damping-off disease was compared with their wild types. Four wild types
isolates belonged to Pseudomonas fluorescens and their mutants
were tested against pre-and post emergence damping-off disease of cotton
in greenhouse. The experiment was conducted in a completely randomized
design with ten treatments and four replicates. A virulent isolate of
Rhizoctonia solani,the causal agent of cotton seedling
damping-off disease was used in the study and the effectiveness of bacterial
isolates was evaluated based on the number of healthy seedlings 15, 30,
45 and 60 days after sowing. Results indicated that all Rif-Nal resistant
mutants showed more effectiveness in disease control than their wild types
15 and 30 days after sowing. However, at days 45 and 60 after sowing,
only three mutants were more effective than their wild types in controlling
cotton seedling damping-off disease. Results of this study suggest that
spontaneous mutation may affect and enhance the activity and performance
of antagonistic bacteria.
