A quantitative model for loss of primary dormancy and induction of secondary dormancy in imbibed seeds of Orobanche spp.

Seeds of three species of Orobanche were conditioned (i,e, stored fully imb ibed in darkness) for periods up to 210 d in order to model relief of prima ry dormancy and induction of secondary dormancy, The data were consistent w ith the hypothesis that periods for loss and induction of dormancy and loss of viability are normally distributed in populations of imbibed seeds and that these three processes are independent, There was a positive, linear re lationship between the rate of loss of primary dormancy and temperature fro m 10-30 degrees C in O, aegyptiaca and O, cernua and 10-25 degrees C in O. crenata, In all three species, the rate of induction of secondary dormancy was highest at 10 degrees C and decreased with increase of temperature up t o about 20 degrees C, above which there was little further change in the ra te with temperature, The resulting model explained over 90% of the variatio n in germination after conditioning in both O, aegyptiaca and O, cernua, In O, crenata, however, this model was only satisfactory at 10 and 15 degrees C, At higher temperatures, dormancy was relatively stable for periods of c onditioning from 70 to about 154 d, Possible explanations for this are disc ussed. Applications of these models for estimating the time required to red uce Orobanche infestations in the field are also briefly discussed.