POST HARVEST SEED QUALITY ASSESSMENT

Abstract

The marketing of seed in New Zealand and the servicing of a large seed export market has traditionally been controlled by the New Zealand Seed Trade. The price which seed commands, however, is capable of wide variation depending on such factors as the overseas demand, the perceived value of the species and cultivar and perhaps by the reputation our seed has in many of the approximately 45 countries who buy seed from New Zealand. In setting the price of a seedlot in any particular selling situation emphasis is also placed on the analytical aspects of seed quality - particularly germination percentage, but also physical purity and freedom from certain weeds, e.g. wild oats (Avena fatua) and nodding thistle (Carduus nutans). In recent years there has become more interest in the term 'quality' in seed. This has lead to a greater interest in the development of relatively quick and reliable seed quality testing methods which can be used to expose seed weaknesses which may not be detected in normal laboratory tests for purity and germination. Various rapid methods for testing seed quality have been developed to allow distinction to be made between seedlots of high potential storability and vigour and seedlots which have already begun to deteriorate. Such tests can also be used to detect possible causes of deterioration and whether this has occurred as a result of mechanical injury during threshing, poor drying technology, damage during processing or seed treatment, or to deterioration due to respiration heating, fungal activity or poor storage conditions. This paper examines the use of post-harvest seed quality assessment techniques such as tetrazolium testing, vigour testing, heat and storage fungal tests, accelerated ageing methods and x-ray analysis for determining seed quality in maize. The methods shown however, may be equally applicable to a much wider range of seed species.