Striga hermonthica (Del.) Benth has Dual Negative Effect on its Host Sorghum bicolor (L.) Moench

Striga is a parasitic weed causing remarkable yield lose in Sorghum bicolor. In this study, phytotoxicity of leaf and flower extracts of Striga hermonthica were investigated on three sorghum varieties under laboratory conditions. Before allelopathic bioassay, total phenolics, alkaloids and terpenoids were quantified in the extracts. For allelopathic bioassay, 5 and 10% (w/v) aqueous extracts were prepared by reconstituting dried crude extracts of leaf and flower of S. hermonthica in distilled water. Varieties of sorghum named Muyra 1 (M1), Muyra 2 (M2) and Fendishe (Fe) were treated with equal amounts of 5 and 10% (w/v) extracts in Petri dishes lined with Whatman no.1 filter paper. The control treatment received distilled water and treatments were laid out in a completely randomized design with three replications. Germination parameters were monitored for 15 days and General linear model was used to analyze data. Results showed that both leaf and flower of S. hermonthica produce phenolics, alkaloids and terpenoids. Values of total phenolics and total alkaloids did not show significant variation, whereas total terpenoid was significantly higher in flower than leaf. Percent germination, shoot and root lengths as well as their dry weights were significantly affected by extract concentration, sorghum variety and their interactions. Compared to control, percent germination and seedling growth were highly reduced at 5% w/v extract concentration and completely inhibited at 10% w/v extract concentration. Varieties were not differentially affected by leaf extracts, but M1 and M2 appeared to be more affected than Fe by flower extract. The result also showed that root growth was more affected by extracts than shoot growth. Overall, this study for the first time revealed that S. hermonthica reduces yield of S. bicolor not only due to parasitism, but also through its negative allelopathic effect on seed germination and early seedling growth.