Invited Review: Seed maturation and its practical implications

The use of high vigour seeds for crop production is increasing in importance. Seed vigour develops during the late maturation phase, after deposition of reserves and attainment of maximum dry weight. During this phase, various protective mechanisms are imposed in the seeds that will aid survival after release from the mother plant. These mechanisms include the production of protective metabolites such as antioxidants and pigments, specific proteins and degradation of chlorophyll. All are essential for maximum quality of seeds used as propagation material, since they aid in providing increased tolerance to diverse biotic and abiotic stresses. Physical sanitation treatments, ageing during storage and threat by pathogens are some of the stresses that the seeds can experience during production, processing and germination. However, harvesting seeds at the fully mature stage and with maximum vigour is a big challenge in seed production. For most seeds, analysis of chlorophyll levels can be used as a measure of relative maturity. This is a rather sensitive technique as it uses the fluorescence properties of chlorophyll, and can also be used for upgrading seed lots containing relatively large fractions of less mature seeds. Sorted seed fractions are also useful to study processes during late seed maturation and the different seed vigour aspects gained during late seed maturation.