Germination response to temperature in tropical and subtropical pasture legumes. 1. Constant temperature

Abstract

The germination response of 13 promising and commonly used tropical and subtropical legumes in northern Australia was tested in the laboratory at 10 constant temperatures ranging from 8 to 447deg;C. Total percent germination for most species was high at temperatures from 16 to 36°C, with Macroptilium atropurpureum, Lablab purpureus and Glycine latifolia germinating well at 12°C. Macroptilium atropurpureum and G. latifolia had less seed death than other species at 8°C. There was no germination at 8 or 44°C for any species. Optimum temperature for rate of germination ranged from 24°C for G. latifolia up to 36°C for Macroptilium bracteatum. Leucaena leucocephala showed a 12-degree range (24-36°C) of optimum temperatures for rate of germination, but most species had a range of 4-8°C. The ability to germinate at a broad range of temperatures indicates that the species are well adapted to northern Australia. Consideration of these responses could be useful in selection of future species or cultivars. Existing linear models with base, optimum and ceiling temperatures, and coefficients of germination rate above and below optimum temperature were tested to predict germination from thermal time. Predicted germination in real time explained 73-90% of the variation in observed germination, with the closeness of fit poor at temperatures distant from optimum. Models using a series of step-wise linear equations describing each 5% interval of germination explained over 99% of the variation in cumulative germination with time, but required a large number of parameters.