In this article we will discuss about:- 1. Need for Seed Storage 2. Importance of Seed Storage 3. Classification of Seed Storage Potential 4. Factors Affecting Storage Life 5. Advantages.
Need for Seed Storage:
The main purpose of seed storage is to secure the supply of good quality seed for sowing whenever needed. The importance of seed storage has been recognized ever since humans began to domesticate plants. The duration of successful storage depends upon both the objectives and the species concerned. Since agriculture began, farmers have had to maintain viable seeds from one growing season to the next (i.e. short-term seed storage, typically 3 to 9 months but occasionally upto 18 months).
It may also be desirable to maintain “carry-over stock” for several years (medium term seed storage, typically 18 months to 5 to 6 years). However, the goal of gene bank is essentially the maintenance of seed viability in a much wider range of species for indefinite periods (long-term seed storage, typically considered as 10 to 100 year or more), a much more difficult task which requires both specific facilities and great deal of information.
Maintenance of seed vigour and viability in terms of germination from harvest until planting is of utmost importance in any seed production programme. To keep vegetable seed for a long time good seed storage is a basic requirement.
Vegetable seed production represents large investment of time, effort and money on which there can be no return until the vegetable seed is sold. Due to any reason, the seeds could not be sold or is surplus need to be stored to preserve its viability and to protect producer’s investment, profit and reputation.
Importance of Seed Storage:
The purpose of storing seeds is to preserve planting stocks from one season until the next. Prehistoric man learned the necessity of this practice and developed methods of storing small quantities of seeds for his future use. As agriculture developed, man expanded his knowledge regarding the requirements for maintenance of seed viability and methods of providing suitable storage conditions.
Beginning with harvest, seed lots usually pass through a series of process necessary for immediate or future use. They include harvesting, curing, drying, cleaning, grading, transporting and storing. Not all commercial seed lots are subjected to all these processes, but the manner in which seeds are passed through each process can affect their storage potential.
Each seed faces an uncertain future. It may be harvested too early, too late, too wet or too dry. The seed future can be affected by being harvested so immature that it cannot germinate or if it germinates, it may produce weak seedling. In the cleaning and grading process the seed may again be subjected to impaction damage which may be due to low moisture content in case of bean.
Radish seed may be damaged severely due to high moisture content during threshing. High moisture makes the seeds difficult to remove from their pods. When transported to market, the seed lot is subjected to storage under various conditions- on the truck, in the railway or in the ships.
Many changes occur in seeds during storage. The principal changes considered in this are three quality factors- germination capacity, vigour and yield potential. Now detailed information exists on chromosome aberration and mutagenic changes in aged seeds as well as biochemical changes related to enzymes, enzymatic action and metabolites.
Classification of Seed Storage Potential:
A large variation in storability is encountered between species. In seed handling terminology, seeds have traditionally been grouped in to two main groups according to their physiological stage potential viz. recalcitrant and orthodox seeds. Raberts (1973) defined two categories of seed storage behavior- Orthodox and recalcitrant. More recently, a third category intermediate between orthodox and recalcitrant categories has been identified.
Orthodox seed include those seeds that can be dried to low (2-5%) moisture content and can, with low moisture content, be stored at low temperature. Seeds of recalcitrant species maintain high moisture content at maturity (often > 30-50 %) and are sensitive to desiccation below 12-30% depending on species.
They have a short storage potential and rapidly lose viability under any kind of storage conditions. A group of species which can be dried to a moisture content low enough to quality as orthodox, but is sensitive to low temperatures, typical for orthodox seeds, has recently been termed ‘intermediate’.
Factors Affecting Storage Life of Seeds:
1. Genetic:
Inheritance of seed longevity is not limited to species. Several cultivars of a specie also differ significantly for seed longevity. The seeds of different plant species vary widely in their lifespan under identical or favourable storage conditions.
2. Pre-Harvest Factors:
Temperature, photoperiod, mineral nutrition, rainfall and soil moisture are important factors for seed viability and storability.
3. Seed Maturity:
There is strong relationship between seed maturity and storability or longevity. The healthy, mature, plump seeds generally store better than immature seeds.
4. Seed Dormancy:
In some seeds, dormancy is caused by seed structure, physiology of the embryo, germination inhibitors and combination of these factors. Storability can be affected by dormancy.
5. Moisture Content:
The moisture content of seeds during storage is no doubt the most influential factor affecting their longevity. It is important to harvest mature, relatively dry seeds or reduce the moisture content of high moisture seeds soon after harvest.
6. Mechanical Damage:
During harvesting and threshing seed can be damaged. Damaged seed, even small and hidden injuries should not be stored.
7. Vigour:
The vigour of seeds at the time of storage is an important factor that affects their storage life. The decline in vigour and viability of seeds is sometime illustrated by a sigmoid survival curve. The survival curve for dry seeds under favourable environmental condition can be divided in to three distinct parts. The first represents the period when the seed is vigorous and decline in the life functions has proceeded slowly.
Eventually this stage ends at a survivable level of 90-75 percent, and deterioration then proceeds very rapidly. After deterioration has proceeded to a survivable level of 25 to 10 percent, it slows again and continues slowly until all seeds are dead (Fig. 5.1).
Advantages of Vegetable Seed Storage
i. The wastage of seed is avoided.
ii. It is easy and convenient to carry over the seed produce from periods of high production to period of using areas.
iii. Storage assures a regular seed supply to the vegetable growers of high quality vegetable varieties/hybrids throughout the year.
iv. It is easy to supply and hold regular trade of vegetable seeds from the seed production areas to the vegetable growing areas.
v. Storage of seed provides sufficient time for the increases in prices of most- vegetable seeds.