Variation in the rate of hard seed breakdown of twelve tropical legumes in response to two temperature regimes in the laboratory

Abstract

Hard seed content is an important factor in the persistence of tropical pasture legumes as both high and low hard seed content can lead to poor recruitment. As temperature plays an important role in the breakdown of hard seed, the patterns of breakdown were measured in 27 seed lots of tropical legumes subjected to temperature regimes of 23–57˚C and 23–70˚C in laboratory ovens for 7 months. The seed lots represented 12 species comprising 15 released cultivars and 5 accessions showing promise in field evaluation studies.

Each month seed was removed for germination testing and the proportion of hard, soft and dead seed in each seed lot was determined. After 7 months, the resulting pattern of hard seed breakdown was modelled to derive threshold temperatures for hard seed breakdown, values for the breakdown rate and quantification of the breakdown process.

Desmanthus virgatus and Indigofera schimperi had the slowest rate of breakdown, while Aeschynomene americana had the fastest. The threshold temperature for most species was in the range 40–50˚C. However, there was considerable variation in threshold temperature and breakdown rates between seed lots of the same cultivar or accession and between species, which indicates that caution must be used before extrapolating the results to the field and to different climatic and/or management environments.

Nevertheless, these results provide valuable information for the development of demographic models of legume persistence, and show that, while the species are well adapted to the temperature environments of northern Australia, specific management may be necessary to enhance the persistence of some of them.