03177nam a2200469 a 450000100080000000500110000800800410001910000190006024501050007926000420018430000270022652019570025365000160221065000130222665000130223965000110225265000160226365000100227965000120228965000160230165000140231765000180233165000150234965000170236465000170238165000130239865000220241165000220243365000120245565300150246765300250248265300210250765300360252865300100256465300220257465300200259665300090261665300200262565300130264565300280265865300210268611635732005-07-04       1984    bl uuuu  m   00u1 u    #d1 aGOEDERT, C. O.  aSeed dormancy of tropical forage grasses and implications for the conservation of genetic resources.  aReading : University of Readingc1984  a190p.cTese Doutorado.  aInvestigation are described on the characteristics of tropical grass seeds affect their management, particularly in genebanks. Five tropical forage grass species were selected for study Brachiaria humidicola, Brachiaria decumbens, Panicum maximum, Paspalum guenoarum and Andropogon gayanus. It is shown that germination tests currently provide the best basis for monitoring viability. However two problems are particularly prevalent in tropical grasses which hinder the interpretation of germination tests; first, freshly harvested seeds often show low purity (i.e. a high proportion of immature and empty spikelets); and secondly, many of the true seeds often show pronounced dormancy (i.e. though viable they are incapable of germination without special stimuli). Investigation of the purity problems showed that in can be overcome with the use of X-ray equipament, but other methods are unreliable. Investigation of the dormancy problem led to the conclusion that advantage needs to be taken of the interaction of several dormancy-breaking agents. It is shown that simultaneous use of three of these are specially valuable alternating-temperatures, linght and nitrate ions. In particular it is important to define the optimum characteristics of alternative-temperature regimes for maximum stimulation of germination. Techniques for doing this were developed using a two-way temperature-gradient plate. Amplitude and thermoperiod were both shown to be particularly important attributes and, although the optima for each species investigated differed in detail, in no case did any optimum diverge far from a regime in which seeds were subjected to diurnal cycles of 20h at 15o and 4h at 35oC in the presence of 10-2 M KNO3 and intermittent illumination. The significance of these and other experimental results are discussed in relation to seed physiology and to the problems of the management of seed accessions in genebanks for genetic conservation.  aagriculture  aagronomy  adormancy  aforage  agermination  aseeds  astorage  aAgricultura  aAgronomia  aConservação  aDormência  aGerminação  aHorticultura  aPastagem  aPlanta Forrageira  aRecurso Genético  aSemente  aForrageira  aGenetic conservation  aGenetic resource  aGramineas forrageiras tropicais  aGrass  aPastagem tropical  aRegiao Tropical  aSeed  aSeed physiology  aSementes  aTropical forage grasses  aTropical pasture