Witchweed’s Suicidal Germination: Can Slenderleaf Help?

The parasitic plant Striga hermonthica (Delile) Benth. is stimulated to germinate by biomolecules (strigolactones) produced in the roots of host and some non-host plants. Non-hosts induce Striga’s suicidal germination and are therefore used as trap crops. Among trap crops, the Slenderleaf legume in the genus Crotalaria (Crotalaria brevidens (L.) Benth.) and (Crotalaria orchroleuca (G.) Don.) has been popularized in African smallholder farms. However, the Striga germination efficiency of these locally grown Crotalaria varieties (landraces) is unknown. Also unclear is Crotolaria’s extent to inhibiting Striga growth, post germination. Extensive parasite penetration can expose the trap crop to secondary infections and possible phytotoxicity from Striga. We used in vitro germination assays to determine the Striga germination efficiency of 29 Crotalaria landraces. Furthermore, we determined Crotalaria’s ability to inhibit Striga attachment and growth using histological analysis. We found that: i) Crotalaria stimulated germination of Striga seeds at frequencies ranging between 15.5% and 54.5% compared to 74.2% stimulation by the synthetic strigolactone (GR24) used a positive control; ii) Crotalaria blocked Striga entry at multiple levels and did not allow growth beyond the pericycle, effectively blocking vascular connection with the non-host. Hence, Crotalaria is suitable as a trap crop in integrated Striga management.