Tissue culture protocols for the obligate parasitic plant Striga hermonthica and implications for host-parasite co-cultivation

Striga is a genus of parasitic plants that poses great danger to livelihoods of millions of smallholder farmers in sub-Saharan Africa by limiting production of staple cereals. The parasite attaches to the roots of the crop and establishes a vascular connection with the host’s xylem vessels in order to access water, organic and inorganic nutrients, leading to stunted growth and death of the infected plant. Mechanisms underpinning host–parasite interactions are not clearly understood making well-informed strategies for control of the parasite difficult. To facilitate studies of Striga–host interactions for molecular and genetic studies, we: (i) established an efficient protocol for growing Striga from seeds in tissue culture; (ii) optimized protocols for its regeneration through direct organogenesis and somatic embryogenesis, and (iii) determined the effect of co-culturing host and parasite in the same culture media. We found the best auxin and cytokinin concentrations to be: 10.7 μM naphthaleneacetic acid (NAA) and 2.2 μM 6-benzylaminopurine (BAP) for embryogenic callus regeneration and 1.1–4.4 μM BAP without NAA for shoot multiplication. While seedling, stem and leaf explants induced callus with the same frequency, seed radicles did not produce any callus. Unexpectedly, we found that when Striga callus was added in rice growing on culture media, the parasite adversely affected the host through formation of lesions on leaves and resulted in less shoot induction from callus in the parasite. Techniques described in this study will enhance further understanding of Striga–host interactions.