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Positive linear relationships were shown between constant temperatures and the rates of progress of germination to different percentiles, G, for single populations of each of five genotypes of chickpea (Cicer anetinum L.). The base temperature, Tb, at which the rate of germination is zero, was 0·0°C for all germination percentiles of all genotypes. The optimum temperature, To(G), at which rate of germination is most rapid, varied between the five genotypes and also between percentiles within at least one population. Over the sub-optimal temperature range, i.e. from Tb to To(G), the distribution of thermal times within each population was normal. Consequently a single equation was applied to describe the influence of sub-optimal temperatures on rate of germination of all seeds within each population of each genotype. The precision with which optimum temperature, Tb(G), could be defined varied between populations. In each of three genotypes there was a negative linear relationship between temperature above Tb(G) and rate of germination. For all seeds within any of these three populations thermal time at supra-optimal temperatures was constant. Variation in the time taken to germinate at supra-optimal temperatures was a consequence of normal variation in the ceiling temperature, To(G)—the temperature at or above which rate of progress to germination percentile G is zero. A new approach to defining the response of seed germination rate to temperature is proposed for use in germplasm screening programmes. In two populations final percentage germination was influenced by temperature. The optimum constant temperature for maximum final germination was between 10°C and 15°C in these populations; approximately 15°C cooler than the optimum temperature for rate of germination. It is suggested that laboratory tests of chickpea germination should be carried out at temperatures between 10°C and 15°C.
Ellis et al. (Wed,) studied this question.