SEED MANAGEMENT
Seed storage behaviour refers to the capacity of seeds to survive desiccation (drying). The periods which seed survives (i.e. its longevity) varies quite a lot among species. It also tends to vary among accessions (collections) within a species, because of differences in genotype and provenance. The influence that provenance and genotype have on the longevity of seed also depends on the following:
-
the cumulative effect of environment during seed maturation e.g. the weather
-
harvesting, drying and the pre-storage environment
-
seed harvest times
-
time it takes to dry the seed
-
the time taken between drying and storage
Accession
Accession is the process of increasing a seed collection or group. It involves collecting seeds from various groups and/or locations of groups, combining them into a single seed lot with the view to storage or planting. This enables the collector or person that later plants the seed to readily determine provenance. Seed can be selected for disease resistance and certain morphological characteristics, (however this could alter in future generations if seed from differing geographical areas are combined; it does however extend the gene-pool). Seed accessions that are collected officially will be allocated a unique number and a Certificate of Provenance.
Species of seeds do not all respond to the environment before or during storage in the same way. Today scientists recognise three main categories of seed storage behaviour:
-
Orthodox species - seeds in this category can be conserved off-site (i.e. outside of their natural environment) for long periods, in appropriate conditions. Collections (accessions) of seeds may vary considerably in their longevity however, irrelevant of the environment in which they are kept. These seeds can be dried to low moisture contents without damage – even lower then they would dry out in nature. The longevity of these seeds increases as the storage environment aids reductions in moisture content and temperature. These are also the easiest seeds to keep long-term. The vast majority of seeds are orthodox species.
-
Recalcitrant species – storage of species with recalcitrant storage behaviour are only viable for the short-term also only in appropriate, well controlled environments. These species do not survive drying to any large degree or freezing – long term storage is not suitable. Moisture levels critical for survival however does vary between species within this group. Seed of recalcitrant species is sometimes processed by cutting out the growing part of the seed, optimising the water content and then rapidly cooling it. Plants from the tropics, riparian zone and temperate zone forests are included for example; oaks, citrus and wild rice.
-
Intermediate species – storage of species which present with intermediate storage behaviour is feasible for the medium-term but only in appropriate, well controlled environments. These seeds tolerate drying better then the recalcitrant species but not as much as the orthodox species. They can withstand partial dehydration but they are cold-sensitive and drying does not increase longevity; they tend to lose viability much more rapidly at low temperatures. They vary from orthodox seeds in the predictability of their longevity in relation to drying and cooling. Intermediate seeds include tropical plants such as such as the oil palm (Elaeis guinensis) and coffee (Coffea arabica), and the Neem tree.
It is essential to know which groups species belong to, in order to determine the most suitable storage facilities, environment and storage length.
