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Routine seed health testing is carried out in most countries for seed certification and plant quarantine. However, the majority of seed health tests used throughout the world have never been subject to rigorous validation. A fully validated test provides for analytical sensitivity, reproducibility and repeatability. Discrepancies between testing methods can occur, leading to costly phytosanitary disputes or liability claims. These issues can be avoided by working toward a system of universally accepted, standardized testing methods on a global level. To ensure that seed health tests are standardized and give reliable and reproducible results in accordance with the given specifications of the test methods, methods should go through a peer review system and/or collaborative study among laboratories. Three primary organizations publish standardized seed health tests: the International Seed Testing Association (ISTA), the International Seed Health Initiative (ISHI), and the U.S. National Seed Health System (NSHS). In 1957, the ISTA Plant Disease Committee (PDC) established a comparative seed health testing program to standardize techniques for detection of seed-borne pathogens. In 1993, the Seed Health Committee (SHC, formerly the PDC) began development of published guidelines for comparative testing. All ISTA validated methods are published in the International Rules for Seed Testing. Additionally, some ISHI-Veg methods have been accepted as ISTA Rules and as Standards by the NSHS. The procedures followed by ISTA, ISHI and the NSHS to achieve global standards in seed health testing are discussed.

The International Seed Health Initiative - Herbage Crops (ISHI-H) has initiated ringtesting to establish international standards for the detection of Clavibacter michiganensis subsp. insidiosus, the causal pathogen of bacterial wilt in lucerne-alfalfa [Medicago sativa) seed. Bacterial wilt of lucerne is a seedborne disease causing wilting, stunting and yellowing of plants. In the field disease symptoms are not severe until the second or third year when significant yield loss can occur. The bacterium can survive in the field for 8–10 years. Because infected seed is a possible source of international spread, phytosanitary regulations are in place in many importing countries. Currently there is no internationally accepted seed test for bacterial wilt.

Laboratory testing of potato plant material for the presence of specific pathogens is an essential component of any efficient seed potato certification program. A professional, commercial diagnostic laboratory must deal with several important issues including sampling, choice of assay method, sample preparation and evaluation of results, laboratory management and certification. A number of these issues will be discussed in this chapter.

Contributors. Preface. Contents. 1. The Economic Importance of the Potato M.F. Askew. 2. Biology, Physiology of the Potato H.D. Rabinowitch, D. Levy. 3. Important Potato Cultivars D.L. Corsini, C.R. Brown. 4. Historical Perspectives of Potato Virus Research R.H. Lawson, R. Stace-Smith. 5. The Main Viruses Infecting Potato Crops A.A. Brunt, et al. 6. Viroids L.F Salazar, et al. 7. Phytoplasma Diseases M. Klein. 8. Transmission of Viruses G.D. Franc, et al. 9. Epidemiology, Field Control of PVY, PLRV D.W. Ragsdale, et al. 10. Detection, Identification of Viruses in Potatoes A. Gera, S. Marco. 11. Isolation, Purification P.E. Thomas, W.K. Kaniewski. 12. Operation of a Commercial ELISA, Seed Testing Laboratory Y. Alon, I. Ben Zeev. 13. Resistance C.R. Brown, et al. 14. Control of Potato Viruses using Meristem, Stem-cutting Cultures, Thermotherapy, Chemotherapy G. Faccioli. 15. Rapid Propagation of Virus-tested Potatoes A.A. Watad, et al. 16. Seed Certification as a Virus Management Tool G.D. Franc. 17. Common Seed Potato Certification Schemes O.A. Gutbrod, A.R. Mosley. 18. Emerging Potato Viruses that Confront Regulations L.G. Brown. Index.

Seed and seedling diseases, root rots, and wilts are caused by a number of soilborne fungi, all of which are facultative saprophytes and can survive in soil for long periods in the absence of a susceptible host. In general, these diseases are serious yield constraints where short rotations or monoculture of legume crops are the rule. Seedling diseases and root rots are enhanced by poor seed vigor, poor seedbed preparation, and other biotic and abiotic stresses which predispose the host plant. Control of these diseases requires an integrated approach of genetic resistance/tolerance, cultural practices, appropriate seed treatments, and high seed vigor. The most economical and durable control of Fusarium wilt is to grow resistant varieties. New races of a wilt pathogen have arisen due to increased selection pressure from growing resistant varieties in short rotations but have not outpaced the development of resistant cultivars.

Random amplified polymorphic DNA (RAPD) has emerged from biotechnological research as a practical genetic identity determinant useful in plant breeding, seed production, and seed testing programmes. This report describes a DNA extraction procedure from dry seeds of maize (Zea mays L.), cotton (Gossypium hirsutum L.), soyabean (Glycine max [L.] Merr.), wheat (Triticum aestivum L.) and red clover (Trifolium pratense L.) that can be successfully employed in subsequent RAPD amplification of DNA fragments. The technique also extracted DNA from dry peanut (Arachis hypogaea L.) seeds, but no amplification fragments were observed following RAPD amplification. This procedure is inexpensive, simple, fast, avoids the use of growing plant tissue, and is applicable to a number of crops.

The features of the three species of the Pyrenophora fungus which cause diseases of barley are summarised in Table 1. Seed transmission is an important feature of the disease complex and therefore seed testing is essential as part of an effective control strategy. Conventional seed health tests are time-consuming and labour-intensive. PCR-based techniques have the potential to overcome these problems. Here we evaluate the potential of the fungal intergenic region for development of a PCR-based detection strategy for these three pathogens. Sequencing of this region has been successfully used in other systems to design specific primers for PCR (Xue et al., 1992).

Ethanol production by seeds was developed as a rapid biochemical test, and found to be a sensitive indicator of seed quality. Seeds of maize, soyabean, cotton, rice and lettuce were aged at 75% relative humidity and 45°C to obtain five aged samples for each species including a nonaged control. Ageing reduced the percentage germination and the coefficient of the rate of germination (CRG). Samples of differentially aged seed lots were subjected to aerobic and anaerobic conditions. Maize and soyabean seeds were imbibed in distilled water while seeds of cotton, rice and lettuce were imbibed with 50 mM glucose in 5 mM potassium phosphate adjusted to a pH of 5.6. Cotton seeds were ground and particles from 3.35 to 4.76 mm were used, while lettuce was scarified. Ethanol was analysed using immobilized enzyme electrode technology and verified by gas chromatography. Anaerobiosis induced greater amounts of ethanol production compared to aerobic treatments. In general, the ethanol production increased with ageing under aerobic conditions while the reverse trend was measured under anaerobic conditions. The anaerobic to aerobic ethanol ratio (ANA ethanol ratio) was calculated and was correlated with the CRG.

Problems associated with traditional methods of evaluating legume inoculants using the most-probable-number plant nodule grow-out test include technician time, expense, growth chamber space, and the length of time (30 days) required to conduct the tests. Through the use of specific monoclonal antibodies, a biotin-labelled intermediate antibody, and streptavidin-labelled magnetic micro-beads, we were able to rapidly remove and purify rhizobial cells from peat inoculants used as quality control samples in the Canadian Legume Inoculant and Pre-Inoculated Seed Testing Program. Viability of the recovered cells was evaluated with a commercial kit employing differential fluorescent nucleic acid probes allowing viability to be rapidly determined via visual examination with a fluorescence microscope. Total elapsed time for complete evaluation of an inoculant was about 90 minutes.

Seeds are a major source of global pathogen dissemination. Detection and characterisation of seedborne pathogens is vital to rational disease control strategies. Our investigations into molecular detection methods resulted in the use of RAPD (Random Amplified Polymorphic DNA) techniques to meet seed testing requirements for speed, specificity and sensitivity. Of the molecular techniques investigated RAPDs were particularly useful because no sequence information was required and polymorphisms occurred within and between species. The technique was successful in amplifying DNA directly from bacterial cells and fungal mycelium, eliminating time-consuming DNA extractions.

Full utilization of seed supplies requires a commitment to improving tree seed technology, with the help of recent advances in seed physiology. Studies of seed maturation have led to new collection and extraction technology which should increase seed yields. Computer analyses of test data allow extension of seed testing beyond simple germination percents to estimates of seed vigor, that elusive quality factor which enables a seed to survive and grow. Basic studies of the germination environment have revealed new information on how temperature, imbibition, and seedcoat microorganisms can be used to obtain vigorous, uniform germination in the nursery bed or container.