Seed Viability and Vigour

Abstract

A viable seed is one which is capable of germination under suitable conditions. The definition includes dormant but viable seeds, in which case the dormancy must be broken before viability can be measured by germination. A non-viable seed, therefore, is one which fails to germinate even under optimal conditions, including treatments for the removal of dormancy. The practical definition of viability depends upon the context in which it is used; for example, to the ecologist, viability implies the ability of the seed to germinate and the ability of the seedling to establish itself in the environment in which the seed finds itself. However, when seeds are utilized, to produce a crop, for example, then viability is a measure of the suitability of the seed batch to produce a satisfactory crop. In order to maintain confidence in their products, commercial seedsmen apply rigorous criteria of quality control. Some of these criteria, including viability, have legally enforced minimum standards for agricultural and horticultural crops (see Chapter 9). In the UK these legal requirements are effective, and the present writer has never been supplied with commercial seed which fell below these standards. Seeds of many ornamental species are regarded as 'difficult', often because they are dormant but sometimes because they readily lose viability. Legal and commercial requirements demand that there must be rigorous consistency in the determination of seed viability. Under the International Rules for Seed Testing (International Seed Testing Association, 1985), precise criteria are defined for testing the viability of all of the main species of crop plants and of many trees. They include the criteria necessary for making a representative sampling of a seed batch, whether it be a bag of seed or a trainload, for the number of test replications, and for the precise conditions of the test for each species. These conditions specify the amount of water necessary, the air temperature, and, through the specification of the substrate, the aeration, the amount of contact beJween seed and moisture, the seed temperature and the illumination. The germination tests J. W. Bradbeer, Seed Dormancy and Germination