The level of hygiene within the store will have a long-term effect on seed quality and longevity. Only seed which has been through the final stages of processing should be taken into the store. All other materials should be excluded. In practice, it is sometimes tempting to use seed stores for short-term retention of other plant materials such as dormant bulbs or selected fruit waiting for seed extraction, but this misuse of the seed store can lead to the introduction of storage pests and pathogens. Plant materials other than seeds are very likely to add to the moisture content of the storage atmosphere. Other sources of water and moisture should also be excluded in order to discourage rats and other rodents.
A comprehensive programme for rodent prevention should be organized from the outset, rather than waiting for any control measures to become necessary later. The possibility of rodent infestation will depend on the method of contain- erization within the store as well as on the location and local conditions.
Rodent prevention and control programmes include the use of rodenticides such as the blood anticoagulants or other proprietary poisons. The material should be used in accordance with the manufacturer’s instructions and current national legislation relating to use of poisons and safety. Other methods to deter rodents from stores and warehouses include the installation of sonic sound systems which are undetectable by workers. The repetitions of sound recordings of birds of prey are also used as deterrents.
Seed stores should not be used for storage or shelter of machinery, appa- ratus or any other materials not directly involved with the stored seed. Additional apparatus and materials make it difficult or even impossible to maintain a high degree of cleanliness. All surfaces should be kept clean and floors should be
cleaned with vacuum cleaners in preference to brooms in order to minimize the build-up of dust. All waste materials should be removed from the store as soon as they are accumulated and disposed of by incinerating safely, as far away from the store as is practical.
Seed stores have a relatively high fire risk due to the dry nature of seed and the possibility of dust in the atmosphere. It is therefore vital that adequate fire prevention measures are formulated and all staff are familiar with them.
A system for entering, locating and retrieving seed lots should be adopted.
The system should take into account the need for sufficient space between seed lots for access and air circulation. Small seed lots should be on suitable shelving and large quantities in bags or sacks should be neatly stacked on pallets.
The most sophisticated seed stores belonging to the larger seed companies have a computerized and fully automated retrieval system. But the main criteria for any system, regardless of the size of operation or level of sophistication, is that all bags, cans or any other form of container must have a label inside and be clearly identified on the outside. Labels must be firmly attached; adhesive labels on tins or other containers should not peel off when subjected to the storage environment. The labels should be written in accordance with the inventory system adopted, which should maintain a record of each seed lot’s year and other details of provenance, designation, samples tested, quantities removed and balance remaining. This information will then always tally with stock books and other records.
The structure and fabric of the buildings should be regularly inspected and any deterioration or damage must be restored immediately by competent tradesmen.
Summary
Definition of storage period
● The overall storage duration starts at harvest and continues until sowing.
● The storage period may be only weeks in some cases, or seed lots may have to be stored for several years.
Harrington’s rule of thumb for seed storage
1. For each 1% reduction in moisture content, the storage life of seed is doubled.
2. For each 5 °C lowering of the storage temperature, the storage life of the seed is doubled.
Reasons for storage
● Contingencies, e.g. poor seed harvest, natural and man-made disasters.
● Fluctuating demand and need to carry seed over to the next season.
● Maintenance of maximum seed vigour and potential germination.
● Maintenance of valuable seed classes, germplasm and breeding material.
Seed store construction and management
● Pay attention to optimum structural requirements so as to maximize stor- age environment requirements.
● Choose store site, considering local year-round weather and environmental conditions.
● Correctly choose structural materials and final surface finishes.
● Attend to potential fire, vermin and safety hazards.
● Instil seed store discipline, including exclusion of all non-seed store materi- als and items.
● Do not store chemical, pesticide or fertilizer materials in the seed store.
Remember the following:
● Most storage insect pests’ activities, including their reproduction, are stim- ulated with seed moisture above about 8%.
● The growth of fungi on seed will commence when the seed moisture con- tent exceeds 12%.
● At a seed moisture content above 18–20%, local heating can occur as a result of total metabolic heat of the biomass; this in turn can be responsible for reducing viability or even spontaneous combustion.
Further Reading
Astley, D. (2007) Banking on genes. The Horticulturist 16(2), 2–5.
Copeland, L. and McDonald, M. (1995) Principles of Seed Science and Technology, 3rd edn.
Chapman & Hall.
Cromarty, A.S., Ellis, R.H. and Roberts, E.H. (1982) The Design of Seed Storage Facilities for Genetic Conservation. International Board for Plant Genetic Resources, Rome.
Justice, J.O. and Bass, L.N. (1978) Principles and Practices of Seed Storage. Agricul ture Handbook Number 505, USDA, Washington, DC.
104 ©R.A.T. George 2009. Vegetable Seed Production, 3rd Edition (R.A.T. George)