The effect of constant and fluctuating temperatures on the permeability of the hard seeds of some legume species

Abstract

Hard seeds of Lupinus digitatus Forsk., Lupinus luteus L., Medicago tribuloides Desr., and Trifolium subterraneum L. (Mt. Barker, Dwalganup, and Geraldton strains) were subjected to constant temperatures of 60 and 140°F, and to fluctuating temperature ranges of 60–115°F, 60–140°, and 60–165°, for a period of 5 months. The temperature fluctuation treatments were set to follow patterns similar to those experienced on the soil surface during the summer months in the agricultural districts of Western Australia. Increased permeability, i.e. an increase in the percentage of seeds permeable to water, took place under all temperature conditions. The lowest increase occurred at a constant temperature of 60°F. A constant temperature of 140° gave a relatively higher increase. All three temperature fluctuation treatments increased the permeability as compared with the constant temperatures, with maximum effect at a range of 60-140°F. Increasing the range to 60–165° did not increase the permeability. With the exception of L. digitatus all species subjected to temperature fluctuations showed a rapid increase in permeability over the first 2 or 3 months. Beyond this point the rate of increase was very slow. The permeability or softening pattern followed by L. digitatus was almost the direct opposite to that of the other species. Of the three strains of T. subterraneum, Mt.. Barker showed the highest increase in permeability under temperature fluctuations and Geraldton the least.