Classification of seeds

Classification of seeds

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  Classification of Seedson the basis of Storage Behaviour (SST 513) Prof. Kumari Rajani Department of Seed Science & Technology Bihar Agricultural University, Sabour
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  Seed Storage The preservationof seeds under controlled environmental conditions which will prolong the viability of the seeds for long periods Seed Deterioration Deteriorative changes occurring with time that increase the seed’s vulnerability to external challenges and decrease the Terminologies seed’s vulnerability to external challenges and decrease the ability of the seed to survive Life Span The average length of life of a kind of organism especially in a particular environment or under specified circumstances OR The duration of existence of an individual Prof. Kumari Rajani
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   In seeds,it is the LENGTH OF TIME that they remain viable.  The life span depends on the species and the environmental conditions under which the seeds are stored. Longevity or Life span of seed  The duration is often qualified by the percentage of seed viability at the end of the period because seedlots are populations in which some seeds die sooner than others (e.g. 85% viability in order to ensure that the majority of individuals in the seed population are viable and in good condition at the end of this period). Prof. Kumari Rajani
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  Ewart (1908) dividedseeds into three biological classes according to their LIFESPAN under the BEST POSSIBLE CONDITION OF STORAGE in which they are capable of retaining viability: 1. Microbiotic (seed lifespan of less than 3 years) 2. Mesobiotic (seed life span of 3 to 15 years) 3. Macrobiotic (seed lifespan of 15 to over 100 years Although Ewart's classes were useful in drawing attention to the differences in natural longevity of seeds of different species, his classification is too rigid to fit the variations between individuals, provenances and seed years in a single species, or the possible variations in storage conditions. Prof. Kumari Rajani
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  Today two majorclasses of seed are recognized (Roberts 1973): 1. Orthodox Seeds which can be dried down to a low MC of around 5% (wet basis) and successfully stored at low or sub-freezing temperatures for long periods. 2. Recalcitrant Seeds which cannot survive drying below a relatively high moisture content (often in the range 20–50% wet basis) andmoisture content (often in the range 20–50% wet basis) and which cannot be successfully stored for long periods. 3. Intermediate Certain seeds do not conform fully either to ortho-dox or recalcitrant category. Some of these seeds may have a limited desiccation tolerance but are sensitive to freezing temperatures. For these seeds, an intermediate category has been suggested by Ellis (1991). Citrus and Coffee seeds may fit this intermediate classification. Prof. Kumari Rajani
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  Orthodox Seeds • Long-livedseeds and can be successfully dried to moisture contents as low as 5% without injury and are able to tolerate freezing. • Desiccation tolerant seeds. • The life span of orthodox seeds can be prolonged with low moisture content and freezing temperatures. Recalcitrant Seeds • Do not survive drying and freezing for ex-situ conservation. • Desiccation intolerant seed • Cannot resist the effects of drying below 30 % moisture content without loosing viability or storage at temperatures less than 10 °C. • Cannot be stored for long periods Classes of seed and freezing temperatures. • Ex-situ conservation of orthodox seeds is therefore, not problematic. • Exemplified by most annual and biennial crops and Agroforestry spe-cies. • Relatively small-seeded. • Ex: Citrus aurantifolia, Capsicum annum, Hamelia patens, Lantana camera, guava (Psidium guajava), Cashew (Anacardium occidentale) and most grains and legume types. • Cannot be stored for long periods like orthodox seeds because they can lose their viability in short period. • Ex: Avocado, mango, Jackfruit, mangosteen, lychee, cocoa, rubber tree, some horticultural trees, aquatic plants, such as Nymphaea caerulea, and several plants used in traditional medicine, such as species of Virola and Pentaclethra. Prof. Kumari Rajani
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  Intermediate seed storagebehaviour Seeds which exhibit the drying tolerance characteristic of the orthodox seeds but are sensitive to low temperature storage like the recalcitrant seeds. Some of these seeds may have a limited desiccation tolerance but are sensitive to freezing temperatures Tolerate desiccation to relatively low moisture content (7 to 10Tolerate desiccation to relatively low moisture content (7 to 10 percent) An intermediate category of seed and has been suggested by Ellis (1991) About 134 species: show intermediate seed storage behaviour. Many of these species are trees of tropical origin, but a few are herbaceous (Hong and others 1996). Prof. Kumari Rajani
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  Examples: 1. Azadirachta indica(Neem) 2. Cinnamomum subaveniu 3. Citrus species 4. Coffea Arabica (Arabian coffee) 5. Coffea canephora (Robusta coffee) 6. Elaeis guineensis (Oil palm)6. Elaeis guineensis (Oil palm) 7. Khaya senegalensis (African mahogany) 8. Lindera megaphylla (Spicewood) 9. Neolitsea parvigemma 10.Swietenia Macrophylla (mahogany) Prof. Kumari Rajani
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  In 1954, seedsof Arctic lupine were recovered from a rodent burrow six meters below the frozen silt in glacial sediments. It was found in the Yukon Territory. Arctic lupine (Lupinus arcticus) Seed longevity in the natural environment The seed was germinated in 1966. Along with the seeds a collared lemming skull was found in the burrow. Since this lemming species disappeared from the region 10,000 years ago it was proposed that the seeds were also of this age. Prof. Kumari Rajani
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  The oldest viableseeds in the world, dating from the Pleistocene era, are not what we thought. New dating techniques have revealed that the seeds, which have been grown into live Arctic lupine plants, are not 10,000 years old as believed. Instead they are likely modern seeds (less than 10 years old) which BUT... Instead they are likely modern seeds (less than 10 years old) which contaminating ancient rodent burrows. Prof. Kumari Rajani
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  Silene stenophylla (narrow-leafedcampion)  An Arctic flower native to Siberia, Russia.  The world’s oldest carbon-14- dated seed that has grown into a viable plant.  The seeds were about 31,800 ± 300 years old.  In 2007, more than 600,000 frozen mature  Three immature seeds contained viable embryos that were extracted and grown in vitro (in test tubes), which grew, flowered and created viable seeds of Oldest Viable Seed  In 2007, more than 600,000 frozen mature and immature seeds were found buried in 70 squirrel hibernation burrows 38 metres (125 ft) below the permafrost near the banks of the Kolyma River. their own. Prof. Kumari Rajani
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  Judean date palm Itis a date palm (Phoenix dactylifera) grown in Judea (Israel). The oldest mature seed that has grown into a viable plant was a Judean date palm seed. About 2,000 years old. Recovered from excavations at Herod the Great's palace on Masada in Israel. It had been preserved in a cool, dry place, not by freezing. It was germinated in 2005 and the plant was nicknamed "Methuselah" after the longest- lived person listed in the Bible. Prof. Kumari Rajani
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  A Japanese botanistfound some viable lotus (waterlily) seeds in a layer of peat under a layer of windblown soil in a dry lakebed in Manchuria (Northeastern China). A geologist classified the peat and loess layers of the lakebed as Pleistocene deposits, but this geologic period the Ice Age in general came to an end 10 thousand to 15 thousand years ago. Sacred Lotus or Indian Lotus (Nelumbo nucifera) The ancient Manchurian seeds are the size of small hazelnuts. They have thick, horny seed coats. They closely resemble the seeds of Nelumbo nucifera (Sacred Lotus or Indian Lotus). Preliminary tests on several whole seeds by the residual carbon 14 isotope method of dating organic carbon residues indicated that the seeds were between 830 and I250 years old. Prof. Kumari Rajani
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  Prediction of SeedStorage Behavior “No single criterion can provide a satisfactory estimation of likely seed storage behavior, but combining information for at least four of the six factors described below may be worthwhile” (Hong and Ellis 1996) 1.PLANT ECOLOGY: From information on seed storage behavior1.PLANT ECOLOGY: From information on seed storage behavior collated for almost 7,000 species from 251 families (Hong and others 1996), it is evident that species that show recalcitrant seed storage behavior do not occur naturally in (i.e. originate from) arid habitats, that is desert and savanna. In such environments, the majority of plant species show orthodox seed storage behavior, while a few may show intermediate seed storage behavior. Prof. Kumari Rajani
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  2. TAXONOMIC CLASSIFICATION:Orthodox seed storage behavior can be found in all species within a few families (e.g. Chenopodiaceae, Combretaceae, Compositae, Labiatae, Solanacea e, Pinaceae), or almost all species in others with only a few exceptional species (e.g. Leguminosae, Graminae, Cucurbitaceae, Cruciferae and Rosaceae). However, most families. 3. PLANT, FRUIT, OR SEED CHARACTERISTICS: Orthodox seed storage behavior is shown by species that produce achenes, many-seeded berries, many-seeded dehiscentachenes, many-seeded berries, many-seeded dehiscent capsules, many dry-seeded pods (but not arillate), many dry- seeded follicles, schizocarps, and utricles (Hong and others 1996). 4. SEED SIZE: Recalcitrant seeds often tend to be larger than intermediate seeds, which in turn tend (on average) to be larger than orthodox seeds. However, there is a very wide range of seed weights or sizes over which seeds of different species show all three types of seed storage behavior (Hong and Ellis 1996). Prof. Kumari Rajani
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  5. SEED MOISTURECONTENT AT SHEDDING: Seed moisture contents at maturity or shedding for species with recalcitrant, intermediate, and orthodox seed storage behavior overlap considerably. 6. SEED SHAPE: There appears to be a weak association between seed shape and seed storage behavior. For example, recalcitrant seeds are often spherical or oval (Chin 1988). Seeds that are thin and flat, shapes that aid natural maturation drying, tend to show orthodox seed storage behavior (Tompsett 1994). Flat seeds tendorthodox seed storage behavior (Tompsett 1994). Flat seeds tend to show orthodox seed storage behavior in Acer spp. (Hong and Ellis 1997b), but show both orthodox and intermediate seed storage behavior in Meliaceae (Hong and Ellis 1998). The spherical form is present in all three categories of seed storage behavior (Hong and Ellis 1997b, 1998). Prof. Kumari Rajani
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  Desiccation tolerance Desiccation tolerancerefers to the ability of an organism to withstand or endure extreme dryness, or drought-like conditions. It is the genetically and metabolically active stage associated with the major loss of water. Desiccation tolerance in certain living organisms provides one Some Terminologies Desiccation tolerance in certain living organisms provides one mechanism of adaptation for survival Tolerance to desiccation permits metabolic activity to be suspended during periods of stress and occurs in a wide variety of organisms, e.g. seeds, pollens, spores of Bryophyta and Pteridophyta, lichens, resurrection plants, viruses, spores of bacteria and fungi, cysts of several Protozoa, dry ova of several Ascaris spp. and dry larvae of several nematodes and insects Prof. Kumari Rajani
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  Imbibition Injury If seedsare immersed (soaked) in water, the rapid uptake of water by dry seeds can result in imbibitions injury 1. the lower initial moisture content of seed 2. the cool temperature at which they imbibe water Most commonly found in Leguminosae and Malvaceae species It can be avoided by conditioning (humidifying) the seeds in a moist atmosphere (close to 100% RH) in order to raise seed moistureatmosphere (close to 100% RH) in order to raise seed moisture contents to 16-18% before the seeds are set to germinate in contact with liquid water. This conditioning takes about 24 hours or more depending on initial moisture content and species It is suggested that seeds at 8% moisture content and below, irrespective of species, should routinely be humidified before germination tests Prof. Kumari Rajani