Mj. Vanhezewijk et Jac. Verkleij, THE EFFECT OF NITROGENOUS COMPOUNDS ON IN-VITRO GERMINATION OF OROBANCHE CRENATA FORSK, Weed Research, 36(5), 1996, pp. 395-404
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.