DNA Replication during Seed Germination, Deterioration, and Its Relation to Vigor in Alfalfa and White Clover

Abstract

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.