Improving seed germination performance of arrowleaf clover (Trifolium vesiculosum)

Context Hardseededness in arrowleaf clover is a known dormancy mechanism. Understanding the characteristics and development of hardseededness can assist in managing sowing, establishment, and persistence of swards. Aim Characterise the germination performance of five arrowleaf clover cultivars, including Cefalu, Seelu, Zulu, Zulu II and Arrotas. Method Seed treatments included mechanical scarification (0, 5, 10, 20, 30 or 40 s), grading into sublots on the basis of colour and density, and time of harvest to evaluate the influence of seed maturity. Seeds were germinated in accordance with International Seed Testing Association (ISTA) guidelines after imposing treatments. Results Physical dormancy preventing water uptake by the seed was found to be the major factor inhibiting germination. Mechanical scarification for 40 s was shown to be the most successful treatment in improving germination percentages in all five cultivars. Seed maturity was found to strongly influence hardseededness. Seeds harvested later not only had a higher level of hardseededness but also a higher percentage germination and rate of germination following scarification than did seeds harvested early in the season. Seeds graded into orange, brown and red sublots contained greater proportions of hard seeds, indicating advanced maturity, than green and yellow seeds, which contained few hard seeds, and took longer to germinate. Germination percentage increased with increasing seed density for seed harvested earlier in the season, but decreased with an increasing density for seed harvested later in the season. The germination percentage of both early and late seedlots increased with increasing density once scarified for 40 s. Conclusion Hardseededness was identified as the major barrier to immediate seed germination in all arrowleaf clover cultivars and seedlots. Scarification improved germination in all seedlots. Maturity also influenced germination percentage and germination rate. Implications Poor establishment in the first growing season could be due to either hardseededness, inappropriate scarification, or that the seed used may have been immature. Colour sorting is likely to result in higher-quality seed. To avoid poor germination in the second year, sowing a mix of scarified seeds and hard seeds that could soften over the course of a year may result in better persistence in mixed pastures.