AZOTOBACTER-CHROOCOCCUM AND STREPTOMYCES-ATROOLIVACEUS AS BIOCONTROL AGENTS OF XANTHOMONAS-CAMPESTRIS PV MALVACEARUM

Seven epiphytic and endophytic seed-borne microorganisms were isolated and identified from cotton seeds (Gossypium barbadense cv. Giza 177). Out of them, Xanthomonas campestris pv. malvacearum Smith and Dye was isolated from disinfected seeds. Seed coated with cells of Azotobacte r chroococcum and Streptomyces atroolivaceus, and seed soaked in the b acterial crude or extracted metabolites and indole-3-acetic acid (IAA) or gibberellic acid (GA3), significantly reduced the disease symptoms and counts of surviving Xanthomonas in the infected leaves. Symptom-f ree leaves and lowest bacterial counts were obtained in plants grown f rom seed soaked in acidic diethyl ether extracts from culture filtrate s of A. chroococcum or S. atroolivaceus. All seed treatments significa ntly enhanced plant growth and fresh weight production. The physiologi cal role of plant growth regulators produced by Azotobacter and Strept omyces in the disease control and plant growth is discussed.