Miller B. McDonald

Seed quality assessment

Growers expect high-quality, genetically pure seed. As a result, seed companies maintain quality control programmes that monitor seed from harvest to purchase. An array of ‘traditional’ seed quality tests, including mechanical tests and tests of genetic purity, seed germination and vigour, and seed health tests, is used, and seed quality assessment techniques continue to evolve. Advances in molecular genetics are allowing the release of new varieties differing essentially in one gene. New molecular biology approaches offer the potential to identify these subtle genetic differences. Advances in seed enhancements, such as pelleting, priming and pregermination, require increased scrutiny of seed quality before and after the enhancement process. New developments in computer imaging for improved purity and germination/vigour analyses are being developed. These novel approaches to seed quality assessment become important as new genetic improvements are conveyed in the seed at increased cost to the grower.

Flowering and Seed Set

Plant reproduction is central to survival of the species. This process is accomplished asexually and/or sexually. Asexual reproduction often is the result of modification of vegetative structures such as stems or roots that possess sufficient fleshy tissue for energy storage. Such structures include rhizomes (bluegrass), corms (gladiolas), bulbs (onion), and tubers (potato). Another form of asexual reproduction is apomixis. Two types of apomixis result in the formation of seedlike structures: vivipary and agamospermy. Vivipary is often expressed by the conversion of the vegetative spikelet or leaf into a somatic structure with reproductive capability. Agamospermy occurs when nucellar (unfertilized) tissue in the embryo sac develops into a diploid egg cell that further differentiates into a “seed.” This form of asexual reproduction requires pollination even though fertilization does not occur. Most plants that reproduce primarily through apomixis also have a limited amount of sexual reproduction. This form of asexual reproduction is generally confined to certain grasses such as Kentucky bluegrass.

Flower seeds : biology and technology

History of the flower seed industry Ornamental bedding plant industry and plug production The uses and potential of wildflower seed Factors affecting flowering Seed development and structure Flower seed physiology and plug germination Seed dormancy in wild flowers Flower seed longevity and deterioration Flower seed production Flower seed cleaning and grading Flower seed priming, pregermination, pelleting and coating Laboratory germination testing of flower seed Tetrazolium testing for flower seeds Vigor testing in flower seeds Conserving herbaceous ornamental plant germplasm

Computer image analysis and classification of giant ragweed seeds

Abstract Giant ragweed exhibits a high degree of polymorphism among individual plants in seed size, shape, spininess, and color. These features may play an important role in giant ragweed seed survival and predation avoidance; however, they are difficult to evaluate because of lack of quantification methods. A computer imaging technique was developed for describing and classifying giant ragweed seeds using digital images of the seed top and side views. Seed samples collected from 20 different giant ragweed plants (classes) were mounted and digitally scanned. Quantitative features were extracted from the seed images, including color, width, height, area, and seed perimeter. A polygon (convex hull) of the seed image based on the seed outline was constructed, from which spininess indices were developed. Fishers linear discriminant with normalized nearest neighbor classification was used to classify randomly selected images of individual seeds according to class (maternal origin), using the extracted features as a database. The best classification rate achieved was 99%, with 138 out of 140 seeds correctly matched using data from both the top and side views. Seed features were easily extracted and varied from 1.2- to 4.5-fold among classes. Area and perimeter measurements varied least within classes but varied most among classes, suggesting that these features discriminate effectively among seeds from different plants in giant ragweed. Convex hull area : seed area ratio, using the seed top view images, was the best index of seed spininess, aligning well with visual assessment and providing greatest discrimination among classes. This experiment shows that in the case of giant ragweed, seeds from different plants are distinguishable in an objective and quantitative manner. This imaging technique can be applied to identification of seeds from different species and to studies on variable seed morphology within a species. Nomenclature: Giant ragweed, Ambrosia trifida L. AMBTR.

Lettuce (Lactuca sativa L.) seed quality evaluation using seed physical attributes, saturated salt accelerated aging and the seed vigour imaging system

High seed quality is essential for optimum stand establishment in lettuce. As a result, it is necessary to have seed vigour tests that permit rapid, objective and accurate evaluation of seed quality. This study evaluated physical and physiological seed quality components of four seed lots of six lettuce varieties obtained from a commercial company. Seeds were evaluated for seedling emergence under greenhouse conditions, standard germination, seed physical aspects, the Saturated Salt Accelerated Aging (SSAA) test and the Seed Vigour Imaging System (SVIS). Results indicated that large-seeded lettuce varieties had higher percentage germination, higher SSAA values, higher SVIS index and more rapid and uniform greenhouse emergence. Black-seeded lettuce varieties possessed higher seed quality and less fungal invasion when evaluated by the SSAA test. The SVIS index significantly correlated with SSAA values and seedling emergence under greenhouse conditions suggesting it can be used as a measure of seed vigour. It is concluded that the SSAA and SVIS tests are practical and accurate determinants of lettuce seed quality and distinguish between high and poor quality lettuce seed lots.

Seed Longevity and Deterioration

Seeds are uniquely equipped to survive as viable regenerative organisms until the time and place are right for the beginning of a new generation; however, like any other form of life, they cannot retain their viability indefinitely and eventually deteriorate and die. Fortunately, neither nature nor agricultural practice ordinarily requires seeds to survive longer than the next growing season, though seeds of most species are able to survive much longer under the proper conditions.

Seed Viability Testing

Although the concept of seed viability is well known, there is considerable disagreement and confusion as to its precise meaning. To most seed technologists and commercial dealers, viability means that a seed is capable of germinating and producing a “normal” seedling. Therefore, it is used synonymously with germination capacity. In this sense, a given seed is either viable or nonviable, depending on its ability to germinate and produce a normal seedling; thus, only seed lots representing populations of seeds may exhibit levels of viability.

Seed Vigor and Vigor Testing

Seeds, as reproductive units, are expected to produce plants in the field. However, farmers and seed producers have long recognized that the labeled germination often overestimates the actual field emergence of seed lots. This occurs because by definition, germination is the “emergence and development from the seed embryo of those essential structures which, for the kind of seed in question, are indicative of the ability to produce a normal plant under favorable conditions (AOSA 2000).” As a result, the standard germination test may fail to provide accurate information concerning a seed lot&s field performance potential for at least four reasons. These include the following.

Seed Vigor and Vigor Tests

Seeds, as reproductive units, are expected to produce plants in the field. However, farmers and seed producers have long recognized that the labeled percent germination often overestimates the actual field emergence of seed lots. This observation is attributed to the objective of a standard germination test which states that germination is the emergence and development from the seed embryo of those essential structures which, for the kind of seed in question, are indicative of the ability to produce a normal plant under favorable conditions. (AOSA, 1991) As a result, the standard germination test fails to provide accurate information concerning a seed lot’s field performance potential for at least four reasons. These include the following.

Seed technology training in the year 2000

A qualidade das sementes devera permanecer como centro das atencoes em programas avancados de producao agricola no proximo milenio. A medida que novas alteracoes ocorrem na agricultura, como decorrencia de avancos da biotecnologia, da tecnologia para aprimorar o desempenho das sementes, da diversidade de exigencias dos consumidores e da evolucao de tecnologia de comunicacao, as empresas de sementes deverao exigir profissionais mais competentes e bem informados para produzir sementes de alta qualidade. Para atingir esse objetivo, uma nova abordagem para o treinamento em tecnologia de sementes e apresentada neste trabalho, baseada no estabelecimento de um consorcio entre tres instituicoes de ensino e pesquisa. Sao, tambem, identificadas vantagens do consorcio, enfatizando-se os pontos fortes especificos de cada instituicao, as vantagens de sua localizacao geografica, representando regioes das mais importantes dos pontos de vista climatico e agricola, com abordagens distintas para o treinamento em tecnologia de sementes, que sao facilitadas pelo avancos da comunicacao global. Essa pode ser a melhor maneira de conduzir o treinamento em tecnologia de sementes nos anos 2000.