Germination responses of a non-dormant seed population of Amaranthus patulus Bertol. to constant temperatures in the sub-optimal range

Abstract. The germination responses of a nondormant seed population of Amaranthus patulus Bertol, at constant sub-optimal temperatures in the range of 10–34°C were analysed through a detailed time-course study. Although a final germination percentage of nearly 100% was attained at temperatures above 18°C, it fell abruptly to zero with decreasing temperature from 17 to 10°C. The final germination percentage, v. temperature plotted on a normal probability scale yielded a straight line, indicating normality of the lower limit temperature within seed population with an estimated mean of 13.75°C and a standard deviation of 1.50°C. Simple linear relationships were obtained between the temperature and the germination rates, i.e., the reciprocals of the time taken to germinate by the subpopulations with 20–80% germination. The linear relationships were characterized by similar base temperatures or theoretical limit temperatures of about 11°C but there was a variation in the required 'thermal times' (θ), the distribution of which could be approximated for the seed population by the following distribution function: where m is the median of the distribution and A is a parameter characterizing the pattern of the distribution. When the germination rates were calculated after subtracting 10–14 h from the time actually consumed in germination, linear Arrhenius relationships were obtained. The apparent activation energy estimated from the linear regression of Arrhenius plot was approximately 100 kJ mol⁻¹ with all 20–80% subpopulations.