Abstract :
Striga hermonthica is a devastating root parasitic weed on cereals. In the present investigation a series of laboratory experiments was undertaken to study the effects of some soil borne bacteria on germination and haustorium initiation in S. hermonthica. A total of 211 bacterial strains and isolates were screened, in a series of preliminary laboratory experiments, for ability to reduce GR24-induced Striga germination. Isolates and strains displaying inhibitory effects (26) were further screened to confirm their suppressive effects on GR24-induced germination, study their influence on Striga germination in response to ACC and on haustorium initiation in response to DMBQ and sorghum root macerate. Striga seeds conditioned in a broth medium inoculated with bacteria showed differential response to GR24 and ACC. Some of the bacterial isolates and strains reduced germination, irrespective of the stimulant used, while others inhibited germination induced by one of the stimulants, but not the other. Haustorium initiation in response to DMBQ and sorghum root macerate showed differential response to bacterial strains and isolates. Some bacterial isolates and strains had no effects on haustorium initiation, while others reduced it, irrespective of the inducing factor. The differential response in germination to GR24 and ACC could be due to bacterial metabolites that curtail production of ACC or its conversion into ethylene. Curtailment of haustorium initiation by bacteria may be attributed to production of inhibitory compounds and/or extracellular enzymes that degrade DMBQ or curtail its production. The study supports the biotic nature of the reported soil suppressiveness to S. hermonthica and indicates that inoculation of soil with bacteria may perturb early developmental stages of parasitism and reduce the devastating effects of the parasite.
