A Model for Germination Responses to Alternating Temperatures

Abstract

When seeds of Chenopodium album are imbibed in 0–01 M potassium nitrate solution in the light at constant temperature, percentage germination increases to an optimum at 24 °C, above which it decreases. These relationships are linear if percentage germination values are transformed to normal deviates. At supra-optimal temperatures, alternating temperatures have little or no effect on this basic relationship. However, at sub-optimal temperatures normal deviate germination increases linearly with amplitude at constant mean temperature and the increases are relatively greater at lower mean temperatures. The effect of amplitude is also greater when more time is spent at the wanner temperature in the diurnal cycle. Seeds of Panicum maximum show very similar responses except that the effect of amplitude is greater when a shorter time is spent at the warmer temperature in the diurnal cycle. These observations form the basis of a quantitative model which, at sub- and supra-optimal temperatures, respectively, accounts for 90 and 75% of the variation in germination of C. album seeds subject to a very wide range of thermal environments on a two-dimensional temperature gradient plate. The data presented for P. maximum are less comprehensive, but again the model accounts for 80% of the variation. The relevance of the same model to two unrelated species from different climates and of different ecological behaviour suggests that it may be generally useful in determining optimum temperatures for seed viability testing regimes and ultimately for predicting field behaviour These results allow the producers to improve the production of homogeneous populations of cyclamen seedlings