Variation in seed softening patterns and impact of seed production environment on hardseededness in early-maturing genotypes of subterranean clover
H. C. Norman A B F , F. P. Smith A B , P. G. H. Nichols B C , P. Si D and N. W. Galwey B D EA CSIRO Centre for Environment and Life Sciences, Private Bag 5, Wembley, WA 6913, Australia.
B Centre for Legumes in Mediterranean Agriculture, University of Western Australia, Crawley, WA 6009, Australia.
C Department of Agriculture Western Australia, 3 Baron Hay Court, South Perth, WA 6151, Australia.
D Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
E Present address: New House, George Green, Little Hallingbury, Bishop’s Stortford, Hertfordshire, CM22 7PP, UK.
F Corresponding author. Email: Hayley.Norman@csiro.au
Australian Journal of Agricultural Research 57(1) 65-74 https://doi.org/10.1071/AR05116
Submitted: 24 March 2005 Accepted: 29 August 2005 Published: 30 January 2006
Abstract
This paper describes variation in the dynamics of seed softening (loss of impermeability) in 20 early-maturing genotypes, including 6 cultivars, of subterranean clover (Trifolium subterraneum L.). It reports the effect of 3 sites of seed production in south-western Australia on the pattern of softening in the first summer–autumn and on total softening over the subsequent 2 years. Seeds were softened at a single field location and in a diurnally fluctuating cabinet (60°C/15°C).
There was significant variation among genotypes in the pattern of seed softening over the first 5 months after senescence. Cultivars Nungarin, Dwalganup, and Geraldton softened most rapidly in late February, whereas cultivars Dalkeith, Urana, and Izmir softened most rapidly in late March. The duration of field exposure required in order for 50% of the first season’s softening to occur ranged from 44 to 108 days among the 20 genotypes. Persistence of hard seeds into the second and third years also varied among genotypes. Of the cultivars, Nungarin and Izmir had the highest levels of residual hard seed after 30 months (5.3% and 3.9%, respectively), whereas Dalkeith had the lowest (0.9%).
Site of seed production had a small but significant effect on both the pattern of softening in the first summer–autumn and the persistence of hard seeds in subsequent years. Seeds produced in a relatively high-rainfall site (768 mm of growing-season rainfall plus supplementary irrigation) had a slower rate of hard seed breakdown than those from either of 2 sites located in the wheatbelt (217 and 423 mm growing-season rainfall). Seed softening through exposure in the field and in a 60°C/15°C fluctuating-temperature cabinet was compared for all genotypes. The cabinet treatment was fairly successful in ranking genotypes for relative between-season hardseededness, although it underestimated total softening by an average of 16%. However, the cabinet treatment was a poor predictor of the within-season pattern of seed softening.
Additional keywords: Trifolium subterraneum, dormancy, seedbank ecology, pasture legumes, persistence, fluctuating-temperature cabinet.
Acknowledgments
This work was funded by the Grains Research and Development Corporation and Australian Wool Innovations through the National Annual Pasture Legume Improvement Programme (NAPLIP). We thank John Stokes at Naraling and Barry Cornish at Nungarin for the use of their properties. We also thank John Titterington, Guy Beazley, Rosemary Lugg, and Duncan Wood for their technical assistance in the laboratory and in sowing and maintaining the field plots. Emma Bermingham and Dean Thomas provided valuable comments on the manuscript.
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