Knowledge of the germination behavior of different populations of a species can be useful in the selection of appropriate seed sources for restoration. The aim of this study was to test the effect of seed population, collection year, after-ripening and incubation conditions on seed dormancy and germination of Stipa bungeana, a perennial grass used for revegetation of degraded grasslands on the Loess Plateau, China. Fresh S. bungeana seeds were collected from eight locally-adapted populations in 2015 and 2016. Dormancy and germination characteristics of fresh and 6-month-old dry-stored seeds were determined by incubating them over a range of alternating temperature regimes in light. Effect of water stress on germination was tested for fresh and 6-month-old dry-stored seeds. Seed dormancy and germination of S. bungeana differed with population and collection year. Six months of dry storage broke seed dormancy, broadened the temperature range for germination and increased among-population differences in germination percentage. The rank order of germination was not consistent in all germination tests, and it varied among populations. Thus, studies on comparing seed dormancy and germination among populations must consider year of collection, seed dormancy states and germination test conditions when selecting seeds for grassland restoration and management.
Differences in seed vigor that arise due to seed aging, even in seeds with high levels of germination, can result in differences in field emergence. Current test methods to identify vigor differences in commercial seed lots with high standard germination take several days to complete. DNA replication, measured using flow cytometry as the ratio of 4C/2C DNA, during early germination of unaged and aged seeds of alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.) was examined as a potential rapid and accurate method of assessing seed vigor. The relationship between 4C/2C DNA during germination of 10 commercial seed lots of both species and their field emergence was also determined. Most of the nuclei in dry mature seeds were arrested in the 2C DNA stage, with only a small proportion of 4C DNA nuclei. The proportion of 4C nuclei increased during germination of seeds, although the increase was lower and delayed in aged seeds with slower and lower germination. The 4C/2C ratio after 24‐h imbibition predicted the field emergence of all seed lots, but particularly of the lots with high standard germination (SG) (SG ≥ 75%, alfalfa, R2 = 0.815; SG ≥ 80%, white clover, R2 = 0.771; P < 0.01). Thus, DNA replication marks an advancement of germination in alfalfa and white clover seed, and the 4C/2C DNA ratio after 24‐h imbibition has potential to predict the seed vigor of both species.
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