Seed quality is crucial to successful seedling production in horticulture

Reliable and uniform establishment in the field and glasshouse is essential in horticultural production both in conventional production of uniform seedlings and plants, and in the production of the rootstock and scion for grafted seedlings. Seed quality, specifically germination and vigour, plays a major role in achieving these aims. Commercial seeds are sold with a standard germination (SG) that is specified to be above a required minimum standard, but seed lots with acceptable levels of SG can show differences in vigour leading to differences in the rate and uniformity of establishment and final emergence. High vigour seed lots emerge rapidly, uniformly and well under a wide range of conditions, compared to the slow, asynchronous and often poor emergence of low vigour lots. High vigour seed lots also show greater longevity during storage. Seed ageing is the main cause of vigour differences and has formed the basis for the development of vigour tests that identify high and low vigour seed lots. These tests enable seed companies to plan their marketing and storage strategies and can be used to provide guidance to growers. Five vigour tests developed within the International Seed Testing Association have been validated for a number of species, with further work on validation in progress. A recently developed test, applicable to a wide range of species, assesses early counts of radicle emergence and can be automated. Research shows that the tests apply to a wide range of species, including legumes, brassicas and cucurbits, as well as onion, pepper, eggplant and flower species. The physiological basis and development of these tests, and their use in identifying characteristics of seed lots that are important to horticulture will be discussed. Differences in seed vigour and the results of vigour tests will be explained in terms of an ageing/repair hypothesis.