Colonization capacity of four Streptomyces isolates in rhizosphere soil of cotton (100 DAS). M1, application of the Streptomyces biocontrol agent by seed coating; M2, application of the Streptomyces biocontrol agent by soil inoculation at the time of sowing. Results are the means of three independent replications. Bars represent standard deviations of the means. Different lowercase letters on top of the histograms indicate significant differences (P < 0.05) according to Duncan's new multiple range test