Search for germination stimulants and inhibitors for root parasitic weeds.

Germination of root parasitic weeds Striga and Orobanche is induced only after an exposure to stimulants in root exudates of host and some non-host plants. Since the isolation and characterization of strigol as the first Striga germination stimulant, five strigol-related compounds, termed strigolactones, have been isolated and characterized as natural stimulants. However, plants seem to produce many other stimulants including novel strigolactones. In addition to these natural stimulants, fungal metabolites, cotylenins and fuscicoccins, and plant hormone jasmonate and its analogues were found to elicit germination of these root parasites. In this paper, characterization and structure-activity relationships of these germination stimulants and other fungal metabolites as germination inhibitors are discussed.