Apr 11, 2003 the seeds of the legumes, in common with those of many other species, have a mechanism of physical dormancy, with water. What kind of seed dormancy occurs in the legume genus. Overcoming dormancy and enhancing germination of sphaeralcea. Seed dormancy causes, types, methods and its importance. Dormancy imposed by impermeable seed coats, dormancy induced by environmental light conditions, and dormancy due to immature embryos at dispersal are just a few of the mechanisms which have been described in different. Comparative study of various pretreatment on seed germination of. Several dormancy mechanisms are suspected to occur in ribes species primarily embryo dormancy resulting from a rudimentary embryo but also seed coat dormancy controlled by growth inhibitors and an impermeable seed coat pfister, 1974. Seed dormancy in cultivation, have highly bred crops such as. Unfortunately, previous studies have not fully characterized the seed biology of any symphoricarpos species. Seed dormancy in cultivation, have highly bred crops such. Mature, freshly shed seeds of palms typically display a combination of underdeveloped embryos morphological dormancy and the inability of developing embryos to rupture covering structures physiological dormancy. Seed dormancy and dormancybreaking conditions of 12 west. Chapter 8 determining dormancybreaking leucanthemum bs. Dormancy of seeds often is associated with seed coat characteristics and is due to the impermeability of the coat to water andor gases, mechanical prevention.
A study with coronilla varia seeds showed that as the depth of a puncture to the seed coat increased, so did the permeability of the seed coat to water. Embryo dormancy of most ribes species can be broken by a long. Differences in permeability to water can be exhibited across a population of seeds, but not for individual seeds. Methods to break seed dormancy of rhynchosia capitata. Seed coat impermeable to water no water uptake caused by genetic or environmental factors aka hard seeds alfalfa, lathryus, red clover, vetches, cotton break dormancy with scarification, hot water, acid, dormancy mechanisms seed coat impermeable to gases no exchange of oxygen or in some cases carbon dioxide.
After 8 h, seeds that were still dormant water impermeable were separated from the water permeable imbibed seeds, and their mass was determined to the nearest 0. Mass of water impermeable seeds was subtracted from original mass, and thus conductivity ds m. Methods for breaking py in the laboratory and germination requirements of water permeable seeds are surveyed. In seeds with py, prevention of water uptake causes the seed to remain dormant until some factors render the. As a result the seed of coesalpinia bonducella l roxb.
Physical dormancy py in seeds is caused by a water impermeable seed or fruit coat baskin and baskin, 1998, 2004, and it is known to occur in only 16 families of angiosperms j. Dormancy class of humboldtia laurifolia seeds imbibition the purpose of this study was to determine whether seeds of h. Thus, seeds are considered dormant when they fall to germinate even though they have adequate light and water, and suitable temperatures for growth which for temperate species are usually in the range of 15 to 30oc. An understanding of seed germination ecology is enhanced by information on kind of dormancy in the seeds, life cycle of the species and seasonal changes in environmental conditions such as temperature and precipitation and soil salinity for halophytes in the habitat from the time of seed dispersal to germination. Seeds with seed coat dormancy usually have a seed coat that is impermeable to oxygen andor water. Legume seed testa and dormancy mechanisms to optimize the time of germination foley, 2001. Under natural conditions these seeds remain on or in the ground without germinating. It is known, or highly suspected, to occur in nine orders and 15 families of angiosperms sensuangiosperm phylogeny group 1998, of which are core eudicots. Classification and ecological relationships of seed dormancy.
Seed coat impermeability and germination of showy crotalaria. The water impermeable status of some species is reversible at a seed moisture. Exogenous physical dormancy is imposed upon the seed from factors external to. Hydrogen peroxide seed scarification of new mexico. Water permeabilityimpermeability in seeds of 15 species. To determine whether seeds were non dormant or dormant due to a water impermeable seed coat, i. Seed germination and seedling growth is a critical step for the abiding. The ecological significance of hard seed includes the ability to rapidly recolonize burnt areas after fire and to withstand ingestion by animals and birds. Mechanical dormancy seed coats are too hard to allow the embryo to expand during germination.
Physical dormancy py occurs in at least 18 angiosperm plant families and is caused by waterimpermeable palisade cells in seed or fruit coats. The water gap can become permeable after exposure to temperature. Water impermeability in seeds with py has also been reported to be due to the waxy cuticle on the outer macrosclereid cells. Pdf determining the phylogenetic and biogeographic distribution of physical dormancy remains a major challenge in germination ecology. Anatomical characters of the seeds ofleguminosae, chiefly general of grays manual. Physical dormancy is the result of impermeable layers that develops during maturation and drying of the seed or fruit.
The genetics and physiology of seed dormancy, a crucial. Pdf dormancybreaking and germination requirements for. Species with water impermeable seed fruit coats have physical dormancy py. Bewlay and black 1994 have divided seed dormancy into two categories, seed coat based and embryo based. Water impermeability of the coat or in some species the fruit. A further increase in water uptake occurs only after germination is completed, as the embryonic axes elongate. Physical dormancy and soil seed bank dynamics in seeds of. Of 260 legume species examined, 85% had some or all impermeable seeds guppy, 1912. Seed dormancy or rest is the innate inhibition of germination of a viable seed even placed in most favourable environment for germination. However, upon water uptake, resumption of metabolism leads to the unavoidable release of vola. The acid did not have the ability to penetrate the seed coat, although water did. Chapter 8 determining dormancybreaking leucanthemum. Depth of the puncture to the seed coat increased, so did the permeability of seed coat of water. Because dormant seeds do not complete germi nation, they cannot enter phase 111.
Morphological aspects such as small, undeveloped embryos. Effects of dry heat on seed germination in selected. Commonly seed dormancy is based on a combination of morphological and physiological criteria. The water impermeability of the testa of hard seed is a physical.
Water permeabilityimpermeability in seeds of 15 species of. Taxonomy, anatomy and evolution of physical dormancy in. Water impermeability in seeds with py has also been reported to. An anatomical structure in the impermeable layers functions as the water gap, seven types of which have been described baskin et al. The palisade layer in the seed coat of water impermeable seeds had no cracks in it, whereas cracks. Pdf a new seed coat waterimpermeability mechanism in.
As a result, the seed is prevented from germinating until dormancy is broken. Physical dormancy in seeds of the holoparasitic angiosperm. This impermeable layer prevents the seed from taking up water or gases. Jun 02, 2016 plant seeds have evolved diverse dormancy forms in response to various climates to maintain viability 2. Breaking of py involves disruption or dislodgement of watergap structures causing the seedsfruits to become water permeable nondormant. Uptake of water by a mature dry seed is triphasic figure i, with a rapid initial uptake phase i followed by a plateau phase phase 11. Germination of woody legume seeds with impermeable seed coats.
In other cases regulation of the rate of water absorption by the seed covering slows the germination process which can be advantageous or disadvantageous depending on the circumstances. Morphology and anatomy of physical dormancy in ipomoea. However, the outer layer develops into the seed coat and becomes impermeable to water in dormant seeds. A class ii knox gene, knox4, controls seed physical dormancy.
Py, imbibition and germination were monitored for mechanically. If physical dormancy breakage is microbially induced in these cases, seeds could persist in a dormant state in. Pdf the proposal is made that seed scientists need an internationally acceptable hierarchical system of classification for seed dormancy. Jul 18, 2008 physical dormancy py is caused by a water. Classification and ecological relationships of seed. However, in a few families, including anacardiaceae, physical dormancy is caused by a water impermeable pericarp baskin and baskin, 1998. Such seed coats develop during the last stages of seed development. This class of seed dormancy is caused by one or more water impermeable layers of palisade cells in the seed coat that impede germination because the seed cannot complete imbibition. Without dormancy, seed would germinate on the standing crop. Macrosclereid cells, a mucilaginous outer cell layer, or a hardened endocarp are three reasons that. The cause of physical dormancy is the structure of the outer cell layer which becomes impermeable to water. Nov 10, 2020 dormancy should be treated by overcoming the problems raised by the impermeable seed.
External seed dormancy may be physical, physicalphysiological, chemical, or mechanical baskin and baskin 1998, 2004. Thus, they do not have a water impermeable layers of palisade cells macrosclereids or a water gap sensu stricto and they imbibe water without the seed coat. Seed dormancy of cardiospermum halicacabum sapindaceae. The role of the testa during development and in establishment. However, a combination of mpd and py is not known to occur in seeds. The genetics and physiology of seed dormancy, a crucial trait. Three replications of 100 seeds were used to calculate moisture content on a fresh weight basis after drying the seed samples at 10328c in a hotair oven for 17 h ista, 1993. For good germination, the seeds of leguminous plants need to undergo a process of scraping, which must be done preferably immediately prior to planting 8.
Physically dormant seeds fail to imbibe water when placed on a wet substrate. There are 3 major mechanisms for imposing dormancy. Baskin and baskin, 1998 is caused by a water impermeable seed coat. In some species the regulation is extreme the seed covering is completely impermeable to water hard seed. Breaking physical dormancy in seeds focussing on the. Occasionally the dormancy is caused by an inhibiting chemical in the epidermis or adjacent interior membranes. Physical dormancy, also termed hardseededness, is an exogenous dormancy caused by a water impermeable hard seed coat. Seeds that have hard, thick seedcoats that physi cally prevent water or oxygen movement into seeds have physical dormancy. Summary historically, physical dormancy, or hard seededness, where seeds are prevented from germinating by a water impermeable seed coat, is viewed as a dormancy mechanism. The seed coat exerts its germinationrestrictive action most of the time by being impermeable to water andor oxygen or by its mechanical resistance to radicle. Seed dormancy can be defined as the state or a condition in which seeds are prevented from germinating even under the favourable environmental conditions for germination including, temperature, water, light, gas, seed coats, and other mechanical restrictions.
Physical dormancy is the most common seed dormancy type seen in the tropics. Evaluating of some treatments on breaking seed dormancy. Seed coats are impermeable in water due to macrosclereid cells, mucilaginous outer cell layer or hardened endocarp. Effect of the seed coat on dormancy and germination in. Water absorption and dormancybreaking requirements of physically. Nonchemical methods to break seed dormancy of canafistula.
Seed coat or seed covering may become hard, fibrous or mucilaginous adhesives gum during dehydration and ripening as a result they become impermeable to water and gases, which prevents the physiological processes initiating germination this type of dormancy is very common in drupe fruits. Two samples each of 15 manually scarified individually with a razor blade and of nontreated intact seeds from the december collection were weighed individually, placed on moistened whatman no. It appears from the literature that dormancy of waterimpermeable seeds may be broken by hot water, dry heat, freezing, organic solvents, acid scarification. Thus, the structure andor chemical composition of the seed coat prevents the seed s water uptake, making germination not possible marcosfilho, 2005. Seed dormancy caused by a water impermeable seed or fruit coat is called physical dormancy py, and it develops during maturation drying of the seed van staden et al. However, dolinski 2009 have presented evidence that dormancy break by heating and by chemical treatment of sida seeds may occur through disruption of the seed. This physical, exogenous dormancy is especially common in species of the fabaceae. Since seed dormancy is a physiological adaptation to environmental heterogeneity, it is a primary factor that in. Water impermeable seed dormancy 367 table i recovery of impermeable seeds fed to livestock adapted from harmon and keim 1934 11 2 germination % nonacid acid treated species recovery before after before after convolvuzus arvensis 23 9. However, dolinski 2009 have presented evidence that dormancy break by heating and by chemical treatment of sida seeds may occur through disruption of the seed coats. The embryo needs to grow inside the seed before the seed can germinate. Seed coverings restrict water uptake, embryo expansion, gas permeability, leaching of inhibitors 2.
The way to determine whether seeds or fruits are imper to water is to weigh them, place them on a moist substrate for 24 blot them dry, and reweigh. Despite such mistreatment, however, the seeds were not destroyed but germinated when sown. Identification and characterization of the water gap in. Morphological characteristics of seeds with physical dormancy. Physical dormancy is found in at least 15 plant families. Showy crotalaria crotalaria spectabilis roth seed dormancy was due to seed coat impermeability to water. Results revealed that hot water treatment was effective to increase the germination rate. Dormancy caused by an impermeable seed coat is known as physical dormancy. If seeds or fruits are impermeable to the surest way to break dormancy is to cut a small hole in the seed or.
Viable seeds that do not imbibe water and thus fail to germinate in an apparently favorable environment are commonly termed impermeable or hard seed. Py and 3 located the site on the seed coat of 11 species where water enters the seed. Physical dormancy py has been documented in 18 plant families of angiosperms no gymnosperms and is caused by an impermeable palisade cell layer in the seed or fruit coat endocarp baskin and baskin, reference baskin and baskin 2014. Dormant water impermeable seeds under dry a, d and wet conditions b, e, showing the release of mucilage in the myxospermous. Physical impermeable layers develops during maturations and drying of seeds this impermeable layer prevent the seed from taking up water or gases. Do soil microbes and abrasion by soil particles influence. The physical dormancy of most seeds was not broken by dry heat or wet heat, but by alternating wet heat and ice water cycles. Methods for breaking dormancy of seeds of tropical forage legumes.
Promoting germination in ornamental palm seeds through. Dormancy provides a strategy for seeds to spread germination in time in. Seed dormancy is an evolutionary adaptation that prevents seeds from germinating during. Chemical or physical abrasion of these water impermeable layer can break physical seed dormancy. The role of various environmental factors in the breaking of py in nature is examined, and the ability of some seeds to cycle between being sensitive to. Germination of woody legume seeds with impermeable seed. Background and aims dormancy in seeds of cuscuta convolvulaceae, tribe cuscuteae is due to a water impermeable seed coat physical dormancy. Intriguingly, however, there is a water gap in the impermeable layer and it is this structure which formed the focus of research into dormancy. Physical seed dormancy in several angiosperm plant families, e. Seed anatomy and water uptake in relation to seed dormancy in. Breaking physical dormancy in seeds focussing on the lens.
Methods for breaking dormancy of seeds of tropical forage. A study of dormancy and germination of seeds ofcercis canadensis. Taxonomy, anatomy and evolution of physical dormancy in seeds. Witchweed seeds preconditioned in distilled water and. Anatomy of two mechanisms of breaking physical dormancy. Physical seed dormancy can be decreased through the development of microcracks on the seed coat 28. Seeds with physical dormancy fail to germinate because the seed is impermeable to water. Sensitivity cycling to physical dormancy break and seed. Physical dormancy plays a key role in protecting seeds against microbial attacks and.
739 73 1087 854 1465 1675 289 348 1350 1581 1322 267 438 1495 1208 701 1128 1659 1515 996 623 222 1548 414 1632 639 1514