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 Azospirillum. A previous study demonstrated that the two organisms (Azospirillum and striga) interacted during cerealroot colonisation. Two strains of A. brasilense isolated from an African sorghum rhizosphere prevented the germination of striga seeds although they were stimulated to germinate by the presence of sorghum roots. Azospirillum cells suspended in a synthetic germination stimulant (GR24) did not inhibit striga seed germination, but did block radicle elongation. Those radicles had an abnormal morphology, and contained no vacuolated cells in the root elongation zone. Lipophilic compounds extracted from the medium of bacteria in the log and stationary growth phases prevented the germination of striga seeds.