THE EFFECT OF NITROGEN ON THE GROWTH AND DEVELOPMENT OF GIANT WITCHWEED, STRIGA-HERMONTHICA BENTH - EFFECT ON CULTURED GERMINATED SEEDLINGSIN HOST ABSENCE

For the first time in sterile nutrient media in the absence of the hos t plant, different forms and rates of nitrogen compounds were screened for their effect on S. hermonthica Benth. shoot development beyond se ed germination. There was no shoot formation beyond the inoculation st ages when S. hermonthica germlings were grown in media devoid of nitro gen source. In culture media containing some nitrogen sources, healthy shoots were formed. Increasing concentrations of KNO3, NaNO3, Ca(NO3) (2), Mg(NO3)(2) and asparagine resulted in a significant increase in S . hermonthica shoot development. Inversely, increasing concentrations of (NH4)(2)SO4, NH4H2PO4, NH4Cl and urea led to increasing significant reduction of S. hermonthica shoot development. The amino acids, glyci ne and asparagine supported reduced shoot development of S. hermonthic a, indicating that organic nitrogen cannot replace inorganic nitrogen for Striga growth. The ammonium nitrogen compounds, (NH4)(2)SO4 and NH 4H2PO4, suppressed further shoot elongation and total dry weight of 20 and 40 days old Striga hermonthica plants, in sterile culture media. The organic compounds urea, allylthiourea and thiourea had an effect s imilar to ammonium compounds. Arginine and glycine on the other hand d id not suppress the further development of the parasite. The suppressi ve effect of nitrogen however, was greater when the parasite was 20 da ys old than when it was 40 days old. This work provides data to show t hat some nitrogen compounds reduce the severity of S. hermonthica atta ck by direct suppression of Striga growth and development at the post- germination stage and after shoots have been formed.