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Master's Dissertation
Full name
Arnaldo Afonso Bellucci
Knowledge Area
Date of Defense
Piracicaba, 1994
Title in Portuguese
Avaliação de populações derivadas de híbridos de milho (Zea mays L.) em cruzamentos nos esquemas dialélico e "top cross"
Keywords in Portuguese
Abstract in Portuguese
O objetivo do presente trabalho foi o de estudar a possibilidade do uso de cruzamentos "top cross" ao invés de díalélicos na avaliação de variedades de milho (Zea mays L.) e do uso de híbridos comerciais como fonte de germoplasma em programas de melhoramento. Para o primeiro objetivo foram instalados dois experimentos sendo um com o dialélico completo sem recíprocos, e um com os cruzamentos "top crosses". Para o segundo objetivo incorporou-se mais um experimento que se constituiu de um dialélico parcial onde foi incluído mais um grupo de variedades. As variedades estudadas constituíram-se de gerações F2 de híbridos comerciais de milho e se tratavam, portanto, de materiais adequados aos dois objetivos. As conclusões foram que cruzamentos "top crosses" podem ser usados na avaliação de variedades desde que não se tenha como objetivo a identificação de cruzamentos específicos mais heteróticos para os caracteres estudados (principalmente produção de grãos) onde o componente heterose específica se mostrou importante, e que os híbridos comerciais são uma fonte muito boa de germoplasma para programas de melhoramento que busquem materiais com bom potencial de produtividade.
Title in English
Diallel crosses ano top-cross for the evaluation of populations derived from maize (Zea mays L.) hybrids
Abstract in English
The objective of the present work was to study the possibility of using the top cross procedure instead of díallel cross for evaluating corn (Zea mays L.) varieties. The experimental material comprized 10 F2 populations from commercial hybrids and their genetics potential as useful germplasm was investigated. For the first objective two trials were carried out: i) a 10x10 complete diallel cross; and ií) a 20 entries experiment comprising 10 F2 populations and the 10 respectiva topcross, using a mixture of the 1 F2 populatíons as testar. Both diallel and topcross experiments were used for evaluating the potential of populations as usefu1 germplasm; for that purpose, a third trial (8x10 partial diallel cross) was also used. The latter comprised eight F2 populations of experimental hybrids besides the ten populations already mentioned. The overall results led to the conclusions that the top cross procedure may be used for the evaluation of maize varíetíes when specific heterosis is not significant or when there is no interest in heterosís in specific cross. Otherwise, the diallel procedure is preferable. It was also concluded that the F2 generations of commercial hybrids showed to be promísing germplasm sources for usíng in hybrid maize breedíng programs.
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