The Influence of Temperature on Seed Germination Rate in Grain Legumes: I. A COMPARISON OF CHICKPEA, LENTIL, SOYABEAN AND COWPEA AT CONSTANT TEMPERATURES

For a single seed population of each of four species of grainlegume positive linear relationships were shown between temperatureand rate of germination for different fractions (G) of eachpopulation, from a base temperature, T_b(G), at which germinationrate is zero, to an optimum temperature, T_o(G) at which germinationrate is maximal. At constant temperatures warmer than T_o(G)there were negative relations (probably linear) between temperatureand rate of germination to the maximum temperature for germination,T_m(G), Within each population T_b(G) did not differ, but it didvary 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, T_o(G) varied both within each populationand also between the four species: 80% of seeds in each populationhad T_o(G) values within the range 31.8?C to 33.8 ?C, 24.0?Cto 24.4?C, 34.0?C to 34.5?C and 33.2?C to >40?C, respectively.Values of T_m(G) were much more vanable: the 80% population rangewas 48 .0?C to 60.8?C for chickpea, 31.8?C to 34.4?C for lentiland 46.8?C to 55.2?C for soyabean; reliable estimates couldnot be made for cowpea, but the results suggest higher and morevariable values of T_m(G) than in the other three species. Atsub-optimal temperatures the distribution of thermal time forthe different fractions of each population was normal, exceptfor lentil where it was log-normal. A single equation is proposedto describe the influence of sub-optimal temperatures on ratesof germination for whole seed populations. At supra-optimaltemperatures, variation in thermal time for the different fractionsof each population was only slight. The implications of thesefindings for the adaptation of grain legume crops to differentenvironments, and for the screening of germplasm, are discussed. Key words: Seed germination rate, temperature, grain legumes