W1168: Environmental and Genetic Determinants of Seed Quality and Performance
Statement of Issues and Justification
The primary biological purpose of seeds is to propagate the species by successfully completing germination and resuming plant growth. Native species have innate mechanisms that regulate their potential for germination, often delaying or timing germination to coincide with optimal conditions for growth. Domesticated crops have lost some, but not all, of these mechanisms, and there has generally been strong selection for rapid and uniform germination of crop seeds. High quality planting seed is the key to successful crop production, but both biological and environmental factors can reduce seed quality. To ensure that society has an abundant supply of high quality seeds, this proposal has established four objectives:1. Determine the influence of pre-harvest stress on seed quality. Environmental stress during seed production frequently reduces seed germination and vigor (Spears et al. 1997), thereby increasing seed costs and limiting supplies of high quality seed to producers. Common environmental stresses that occur during seed development and maturation include high or low temperature stress and moisture stress. A better understanding of the impact that environmental stress has on seed quality will result in methods to ameliorate those effects and consistently produce higher quality seeds.
2. Identify the biophysical, biochemical and genetic factors governing seed desiccation tolerance and longevity. The desiccation tolerance of orthodox seeds permits them to survive from one growing season to the next and facilitates long-term storage of plant germplasm and seeds in commercial inventory. It is well known that seed vigor increases until physiological maturity when the seed has acquired its maximum dry weight, although there remains debate about whether vigor continues to increase subsequently during dehydration (TeKrony and Egli 1997). Not all seeds, however, are desiccation-tolerant (termed recalcitrant seeds) and storage of such germplasm that has little or intermediate tolerance of desiccation can be problematic. Successful seed storage is economically important. Approximately 25% of seed inventories are lost annually at a cost of $1 billion. In order to understand the factors that contribute to physiological maturity, desiccation tolerance and storage longevity, it is necessary to understand the physical forces that arise during dehydration and the factors that govern the kinetics of seed ageing. In desiccation-sensitive cells and tissues, these forces cause lethal damage, while tolerant cells and tissues ameliorate these effects to facilitate seed survival (Walters 1998). This objective will improve seed storage and significantly reduce the loss of seeds stored in commercial inventory and in long-term germplasm banks.
3. Identify genes associated with seed development, germination, vigor and dormancy. Genetics and genomics are powerful tools for investigating diverse developmental, physiological and biochemical processes. With respect to seed biology, considerable effort in model systems such as Arabidopsis thaliana and in major agronomic crops has identified a large number of genes involved in embryogenesis, reserve accumulation and seed maturation (Larkins and Vasil 1997). A significant number of genes are known to be associated with seed germination and with its regulation by hormones or dormancy (Finkelstein et al. 2002; Koornneef et al. 2002). However, relatively few of these reveal actual mechanisms by which germination is initiated or inhibited. Very little is known about the genes involved in seed vigor, although there are clearly genetic determinants of vigor (e.g. Eagles and Hardacre 1979). Identifying both regulatory and mechanistic genes involved in seed development, germination, vigor and dormancy would have clear application to the production and utilization of high quality seed for agriculture. Knowledge of specific genes and alleles conferring desirable or undesirable seed traits could guide molecular-assisted breeding strategies to improve seed quality. Greater understanding of the determinants of seed performance as propagules is also required to predict how genetic modifications of seed composition will affect the ability to use such seeds as planting material. The specific projects proposed here will contribute to this overall goal of identifying and characterizing the genes that determine seed quality and performance in the broad sense.
4. Develop technologies to assess seed quality, improve seed performance and enhance seed utilization. Methods are needed that assess the germination potential of a seed lot in a rapid and objective manner. Seeds that do not meet quality expectations can be subjected to enhancement methods to overcome dormancy mechanisms and/or to further improve germination rate (Taylor et al. 1998). These enhancements include physical or physiological treatments, and methods to protect or eradicate seed pathogens and pests. As these technologies are often species- and application-specific, further research is needed to extend and adapt these methods to additional species and markets. Such technologies will better assess and enhance seed quality and result in improved seedling establishment and crop performance.
Developing solutions to these issues is central to the provision of an abundant supply of high quality seeds for successful stand establishment in agriculture. These issues are also complex, requiring unique skills, equipment and methodologies. Utilizing a multi-state effort as described here by drawing on the expertise of specialized research scientists is the most efficient approach to addressing these issues. Successfully completing the four stated objectives will provide not only an increased understanding of the factors that influence seed biology but also improved seed performance in the field.
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