Isolation of Pathogenic Bacillus circulans from Callus Cultures and Healthy Offshoots of Date Palm (Phoenix dactylifera L.)

Pure cultures of a gram-negative, rod-shaped bacterium, which produced endospores after 3 to 5 days on solid medium, were isolated exclusively from tissue cultures of the date palm Phoenix dactylifera L. Electron microscopic examination of thin sections of the bacteria revealed the bilayer membrane typical of gramnegative bacteria and confirmed the nature of the spores as true endospores. Biochemical and physiological tests indicated that the bacteria were Bacillus circulans. B. circulans was consistently isolated from the internal tissues, including the meristem, of apparently healthy offshoots of date palm. When meristem and embryo callus tissue culture samples were injected with B. circulans isolated from similar tissue culture samples and from offshoots, the majority of the isolates produced a rapid, destructive soft rot of the tissues.