AN INVITRO GROWTH SYSTEM FOR STUDYING THE PARASITISM OF COWPEA (VIGNA-UNGUICULATA) BY STRIGA GESNERIOIDES

An in-vitro growth system for investigating the behaviour of S. gesnerioides on cowpea has been developed. The roots of young cowpea plants were spred over glass fibre filter paper in a shallow plastic tray, and a known number of germinated Striga seeds were placed on the cowpea root surface. This allowed the infection process of the parasite to be quantified. Good access to the host-parasite association the entire infection process to be easily monitored and tissue removed for cytological studies. Observations revealed for the first time that contact of S. gesnerioides radicles with host roots stimulated the development of radicular hairs and swelling of the tip of these radicles. Furthermore, penetration of cowpea roots by Striga was shown to the localized and to cause very little damage to the host roots. Swollen parasite tubercles developed on the surface of the roots only after the host stele had been penetrated by invading Striga cells. This growth system is suitable for investigating the mechanisms of host resistance, and also for rapidly screening cowpea germplasm for new sources of resistance to the parasite. Resistant cowpea cultivars offer the best potential solution for control of this parasite.