|
|
| Storage & Conservation |
|
If seeds are stored properly, they can last from a few years to centuries, depending on the species
|
| Introduction |
|
Proper storage of seed is vital to conserving its vigor and vitality. Seeds can last from a few years to centuries, depending on the species and the storage conditions. In general, most seeds stored in cool, dry conditions will survive longer than seeds stored in a wet, warm environment. In many parts of the world, agricultural seeds are stored in bins that are open to the ambient conditions, often resulting in short storage life and poor seed quality in hot, humid regions, as well as losses due to insects and rodents. As the viability period for seeds decreases by half for every 1% increase in seed moisture content or 10°F (~5°C) increase in temperature, sealed bins and controlled environments are used to maintain seed viability for longer periods. A common rule of thumb is that the temperature (in Fahrenheit) plus the relative humidity in the air (in percent) should total less than 100 for satisfactory seed storage.
At seed banks that store seeds to preserve genetic diversity, seeds are dried to optimum moisture content, evaluated for quality and genetic purity and sealed in moisture-proof containers. For short-term storage, seeds are dried and placed in sealed containers at 5°C. They are stored at temperatures below freezing for long-term preservation (0°F or -20°C), including the use of cryopreservation, or freezing in or over liquid nitrogen at -180°C, for extremely long-term storage. But when it comes to seed storage, one size does not fit all. Some species have short-lived seeds that do not tolerate dehydration and are therefore difficult to store. Plants producing these recalcitrant seeds must be maintained as living populations, making them vulnerable to loss due to changes in land use or weather patterns.
The vigor and viability of seeds stored even at low temperatures declines over time. The continued maintenance of specific seed lines requires that they periodically be removed from storage and used to produce a new crop of seeds. Seed storage facilities therefore need not only modern storage equipment but also the land, personnel and expertise to periodically grow the stored seeds under conditions that maintain their genetic diversity and purity in order to replenish the original seed stock. Thus, core seed repositories such as the U.S. National Center for Genetic Resources Preservation in Ft. Collins, Colorado, are complemented by a number of branch stations in different growing environments to store and replenish seed collections of diverse species.
| Recalcitrant seeds |
Recalcitrant seeds are seeds that do not survive drying and freezing and therefore cannot be stored for long periods of time. Some plants that produce recalcitrant seeds include avocado, mango, lychee and some horticultural trees. |
|
|
| Genetic purity |
|
Genetic purity refers to the percentage of contamination by seeds or genetic material of other varieties or species.
The genetic purity of any commercial agricultural product propagated by seed begins with the purity of the seed planted.
In general, the genetic purity of the seed planted must equal or exceed the final product purity standard required, as purity generally decreases with each subsequent generation of propagation.
It is virtually impossible to assure that no off-type plants or pollen is present in the seed production field and that all handling and conveyance equipment and storage facilities are completely free of contamination.
As a result, commercial planting seed is seldom 100% pure. In practice, practical seed genetic purity standards have been established by state seed laws and by seed certification agencies to ensure that the purchaser receives seed that is within certain purity tolerances.
These tolerances are established based on the biology of the species (i.e., self- or cross-pollinated), the type of variety (i.e., open-pollinated, hybrid, synthetic), and market-driven standards for final product quality.
Earlier generations of seed (e.g., foundation or registered seed) have stricter standards in order to be able to meet the certified seed purity criteria.
The main sources of contamination of a seed crop are the prior crop grown in a field, transfer of pollen from a nearby field, and mixtures during harvesting and handling.
|
| Coexistence |
|
Co-existence for crop agriculture can be defined as the sustainable production of seed, food and fiber from diverse plant varieties, crop types and production practices.
Co-existence principles have been the key to successful diversification of plant varieties and production systems for food and seed as practiced by growers and shepherded by national and international seed associations from 70 countries over the last 100 years (AOSCA, 2008; ISF, 2008).
The foundation of co-existence is good communication among growers, handlers, shippers and marketers and respect for each others’ practices and requirements.
There is general agreement in agriculture that a zero tolerance or 100% purity standard is not practical in field production systems, but tolerances and thresholds for the presence of low levels of undesired materials allow efficient marketing while meeting end use quality and safety criteria (FDA, 1998).
It is customary that the primary responsibility for meeting specific market standards is on the entity economically benefiting from it, usually the producer who is compensated for higher quality products (CropLife, 2006; Fernandez and Polansky, 2006; SCIMAC, 2006).
SOURCES
|
| Certification programs |
|
Seed certification programs have been in existence for over 100 years. They have effectively defined and monitored standards to guarantee specific purity standards of the final product or seed. The standards developed reflect the genetic purity and quality of the final product (including seed) based on the final market requirements.
Seed classes: breeder, foundation, registered, certified, commercial, variety undeclared
U.S. National Organic Program (NOP)
The National Organic Program (NOP) in the United States (USDA, 2005) and several other countries define production practices that must be adhered to in order to market products and seeds bearing an “Organic” label. These programs are processed-based rather than being based on the final quality of the product. For example, although only certain approved compounds with pesticidal or fertilizer properties may used in producing organic seed or products, minimum thresholds are established for the inadvertent presence of non-approved compounds. To produce organic products in the US, growers must first begin with organically produced seed. If it is not available, they can use seed that has not been treated with unapproved (usually synthetic) compounds. Although organic programs have chosen to exclude genetically engineered (GE) varieties from the program, there are no established thresholds for the presence of GE materials in organic products. In fact, as long as growers follow an NOP-approved production plan, the USDA has assured that they will not lose organic certification if GE materials are inadvertently found in their seed or products.
SOURCES
ARTICLES
The California Crop Improvement Association (CCIA)
By Diane Nelson, Writer, University of California, Davis, Department of Plant Sciences
|
| Hybridity and varietal purity tests |
|
Hybrid seed is seed produced by cross-pollinating plants in a controlled environment.
Hybrids are bred to improve the characteristics of the resulting plants, such as better yield, greater uniformity, improved vigor, color, disease resistance, and so forth.
Today, hybrid seed is predominant in agriculture and home gardening, and is one of the main contributing factors to the dramatic rise in agricultural output during the last half of the 20th century.
In the U.S., the commercial market was launched in the 1920s, with the first hybrid maize.
Hybrid seed cannot be saved for replanting without losing the benefits of the original variety as these traits randomly segregate among the saved seed, not reliably producing true copies of the original variety.
New seed must therefore be produced for each planting.
As genetic purity is a function of seed production, each hybrid seed lot must be tested for parentage and purity. To achieve this, hundreds of seeds from each seed lot are planted and observed for uniformity in field tests.
Protein and DNA molecular marker analyses are also widely used for hybrid purity testing.
Protein analysis is often prefered because it is less expensive, but DNA tests are becoming increasingly affordable.
Similar tests are applied to open-pollinated and synthetic varieties to assure varietal purity.
|
|
|
|
