The Influence of Temperature on Seed Germination Rate in Grain Legumes

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Abstract
For a single seed population of each of four species of grain legume positive linear relationships were shown between temperature and rate of germination for different fractions (G) of each population, from a base temperature, Tb(G), at which germination rate is zero, to an optimum temperature, To(G) at which germination rate is maximal. At constant temperatures warmer than To(G) there were negative relations (probably linear) between temperature and rate of germination to the maximum temperature for germination, Tm(G), Within each population Tb(G) did not differ, but it did vary between species, viz.0.0°C, 0.25°C, 4.and 8.5°C for chickpea (Cicer arietinum L.), lentil (Lens culinaris Medic.), soyabean (Glycine max [ Merr.) and cowpea (Vigna unguiculata [L.] Walp.), respectively. In contrast, To(G) varied both within each population and also between the four species: 80% of seeds in each population had To(G) values within the range 31.8°C to 33.8 °C, 24.0°C to 24.4°C, 34.0°C to 34.5°C and 33.2°C to >40°C, respectively. Values of Tm(G) were much more vanable: the 80% population range was 48 .0°C to 60.8°C for chickpea, 31.8°C to 34.4°C for lentil and 46.8°C to 55.2°C for soyabean; reliable estimates could not be made for cowpea, but the results suggest higher and more variable values of Tm(G) than in the other three species. At sub-optimal temperatures the distribution of thermal time for the different fractions of each population was normal, except for lentil where it was log-normal. A single equation is proposed to describe the influence of sub-optimal temperatures on rates of germination for whole seed populations. At supra-optimal temperatures, variation in thermal time for the different fractions of each population was only slight. The implications of these findings for the adaptation of grain legume crops to different environments, and for the screening of germplasm, are discussed.