02757nam a2200349 a 450000100080000000500110000800800410001910000200006024500460008026000410012630000100016750000180017752019230019565000130211865000210213165000110215265000150216365000160217865000150219465000140220965000120222365000200223565300120225565300310226765300160229865300130231465300210232765300120234865300090236065300190236965300190238815592411999-10-22       1991    bl uuuu  m   00u1 u    #d1 aPIETA FILHO, C.  aCereal seed development and seed quality.  aReading: University of Readingc1991  a205p.  aPh.D. Thesis.  aIn order to determine when maximum seed quality was attained, changes in quality were monitored during seed development in spring and winter cereals in 1988 and 1989. Seed longevity was determined at 40oC with 15%-+ 0.5% moisture content for seed samples harvested serially fron developing seed crops of: two spring wheat cultivars and two spring barley cultivars in 1988; two winter wheat cultivars and two winter barley cultivars in 1989; and in one spring barley cultivar subjected to post-anthesis shading in both years. A seed storage regime was selected from the results of an initial laboratory experiment; subsequent comparisons with field emergence and standard laboratory germination showed that longevity was the most senstive indicator of changes in seed quality. Shading developing barley seeds: reduced seed dry weight substantially in both years; had little effect on seed longevity; but reduced seedliing size. Physiological maturity, defined as the stage in development when seeds attain maximum dry weight, ocurred before maximum seed quality was achieved in every case. Maximum seed quality generally occurred between 10 and 20 days after physiological maturity, when maturation drying had reduced seed moisture contents to between 14% and 28%; i. e. the timing of maximum seed quality was achieved closer to harvest maturity (16% moisture content) than to physiological maturity. Consequently, the hypothesis that maximum seed quality coincides with phsiological maturity and declines thereafter, is rejected. Cereal seed producers, in order to ensure high quality seeds, are recommended to harvest seeds, 1) In a wet season, when seed miosture content has fallen to around 20%, and then to dry artificially. 2) In a dry season, harvest seeds at or less than 16% moisture content.I suggest that similar invetigatons are carried out to determine when maximum seed quality occurs in other crop seeds.  ahumidity  aplant physiology  aCereal  aFisiologia  aLongevidade  aMaturidade  aQualidade  aSemente  aTeor de Umidade  aCereals  aFisiologia teor de umidade  aLongividade  aMaturity  aMoisture content  aQuality  aSeed  aSeed lingevity  aSeed longevity