Host Range and Germination Stimulant Specificity of Striga gesnerioides Parasitizing Cowpea Varieties

Abstract

Striga gesnerioides (Willd.) Vatke (witchweed, Orobanchaceae) is an obligate root hemiparasitic angiosperm of devastating economic and agronomic consequence in sub-Saharan African cowpea (Vigna unguiculata [L.] Walp.) production systems, inducing severe stunting, chlorosis, wilting, and complete crop failure under high parasite pressure conditions while simultaneously depleting soil moisture, nitrogen, and other essential mineral nutrients that compromise the productivity of subsequent crops in rotation sequences. Despite the recognized significance of host range determination and germination stimulant specificity as fundamental parameters governing S. gesnerioides parasitism dynamics and the differential susceptibility of cowpea germplasm to infection, comprehensive investigations characterizing the breadth of potential host range across cowpea varietal diversity and quantifying the chemical ecology of seed germination stimulation remain insufficiently resolved, limiting the formulation of cultivar selection criteria and integrated management frameworks calibrated to regional parasite populations. This study systematically evaluated the host range of S. gesnerioides across a diverse panel of cowpea varieties representing cultivated germplasm diversity, local farmer-preferred landraces, and wild Vigna relatives, employing standardized in vitro seed germination assays and controlled pot trials under greenhouse conditions to assess differential susceptibility to parasitism. Host root exudate collections from candidate host and non-host plant species were analyzed through high-performance liquid chromatography and gas chromatography-mass spectrometry to characterize the chemical composition and concentration of stimulant compounds responsible for seed germination induction across the surveyed germplasm. Synthetic and semi-synthetic formulations of identified germination stimulants were prepared and evaluated in dose-response experiments to establish quantitative relationships between chemical concentration and S. gesnerioides seed germination probability. Field validation trials were conducted across representative cowpea production environments to confirm greenhouse-derived germination specificity relationships and assess the practical feasibility of exploiting germination stimulant variation for resistance breeding or trap crop deployment strategies.