THE EFFECT OF NITROGENOUS COMPOUNDS ON IN-VITRO GERMINATION OF OROBANCHE CRENATA FORSK

The effect of nitrogen (ammonium, urea and nitrate), applied during a conditioning or germination phase, on germination of Orobanche crenata Forsk. seeds was investigated in vitro. Ammonium sulphate (8 mM) appl ied during conditioning in combination with the nitrification inhibito r nitrapyrin, reduced germination of seeds from 46% to 26%. A lower co ncentration of 4 mM ammonium sulphate or supplying nitrogen as 8 mM ur ea or 16 mM nitrate did not inhibit germination, Applied after conditi oning during the germination phase, 4 mM ammonium sulphate strongly in hibited germination, especially in combination with a nitrification in hibitor: germination was reduced to less than 5%. Urea (8 mM) reduced germination to only a limited extent (from 58% to 40%). When a urease inhibitor (carbon disulfide) was additionally applied, germination per centage was not affected. Nitrate had no effect. It is hypothesized th at the inhibition by ammonium of O. crenata germination is connected w ith a reduced activities of the enzymes GS and GOGAT. The inhibitory e ffect of urea may be indirect, occurring through conversion to ammoniu m. The effect of a short-term exposure to ammonium was largely reversi ble and no increase in mortality culd be detected. The presence of 6 m M phosphate, Hepes or Mops buffer was found to intervene with the inhi bition by ammonium.