Physiological and cytological studies on the inhibition of Striga seed germination by the plant growth-promoting bacterium Azospirillum brasilense

Striga hermonthica (Del.) Benth. is an obligate parasitic weed of tropical cereals whose rhizosphere can also be colonised by bacteria of the genus Az ospirillum. A previous study demonstrated that the two organisms (Azospiril lum and striga) interacted during cerealroot colonisation. Two strains of A . brasilense isolated from an African sorghum rhizosphere prevented the ger mination of striga seeds although they were stimulated to germinate by the presence of sorghum roots. Azospirillum cells suspended in a synthetic germ ination stimulant (GR24) did not inhibit striga seed germination, but did b lock radicle elongation. Those radicles had an abnormal morphology, and con tained no vacuolated cells in the root elongation zone. Lipophilic compound s extracted from the medium of bacteria in the log and stationary growth ph ases prevented the germination of striga seeds.