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Citogenética e potencial forrageiro de combinações genômicas de capim-elefante e milheto
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UNIVERSIDADE FEDERAL DE LAVRAS
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Visando contribuir com o programa de melhoramento do capim-elefante da Embrapa Gado de Leite, combinações genômicas resultantes do retrocruzamento do híbrido hexaploide com seus parentais capim-elefante e milheto foram avaliadas para características citogenéticas, anatômicas e agronômicas/bromatológicas. Pennisetum purpureum (2n=4x=28, genomas A´A´BB) e Pennisetum glaucum (2n=2x=14, genomas AA) produzem o híbrido triploide de constituição genômica AA´B, que reúne características forrageiras superiores de ambos os progenitores, porém, é estéril devido ao pareamento irregular dos cromossomos na meiose. Submetido à duplicação cromossômica com utilização de antimitóticos, obtém-se o hexaploide de constituição genômica AAA´A´BB. As combinações genômicas AA´A´BB e AAA´B, resultantes do retrocruzamento do hexaploide com o capim-elefante e hexaploide com milheto, respectivamente, apresentaram elevado grau de mixoploidia, com o número cromossômico dos pentaploides variando entre 20 e 34, sendo 28 o mais frequente e os tetraploides com número cromossômico entre 16 e 28, sendo 21 o mais frequente. A variação do número cromossômico foi maior nas combinações genômicas pentaploides do que nas tetraploides. A citometria de fluxo demonstrou que ocorreu perda de DNA nas combinações genômicas, variando de 14,71% a 19,00%, nas tetraploides e de 9,25% a 14,45% nas pentaploides. Os estômatos das combinações genômicas tetraploides tenderam a ser menores e mais numerosos que o das pentaploides. A utilização da contagem cromossômica e da citometria de fluxo foi mais eficaz que a anatomia de estômatos para a caracterização das combinações genômicas. A combinação genômica HCM-5x-2 destacou-se entre os pentaploides quanto à produção de matéria seca de forragem e a combinação genômica HCM-4x-2 destacou-se, entre os tetraplóides, para a mesma característica. A melhoria da qualidade forrageira em Pennisetum por meio da introgressão de características favoráveis do milheto foi evidenciada pelo melhor desempenho das combinações genômicas pentaploides para características bromatológicas, mostrando o potencial das mesmas para inclusão em programas de melhoramento genético.
Aiming at contributing to the elephant grass improvement program of the Embrapa Gado de Leite, genomic combinations resulting from the backcrossing of hybrids with its parental hexaploid elephant grass and pearl millet were evaluated for cytogenetic, anatomical and agronomic/ bromatological characteristics. Pennisetum purpureum (2n = 4x = 28, genomes A'A'BB) and Pennisetum glaucum (2n = 2x = 14, genome AA) produce the triploid hybrid with genomic formation AA'B, gathering superior fodder characteristics from both parents. However it is sterile due to irregular pairing of chromosomes in meiosis. When antimitotic agents were used in order to double the chromosomes number, the hexaploid of genomic constitution AAA'A'BB is obtained. The AA'A'BB and AAA'B genomic combinations resulting from the backcrossing of hexaploid with elephant grass and hexaploid with pearl millet, respectively, showed a high degree of mixoploidy. The pentaploids chromosomes number ranged from 20 to 34, and the most frequent ones numbered 28. The tetraploids chromosomes number ranged from 16 to 28, and the most common ones numbered 21. More variation was noticed in the chromosomes number of the pentaploids genomic combinations than in those of tetraploids. Flow cytometry showed DNA loss in genomic combinations which ranged from 14.71 to 19.00% in tetraploids and from 9.25 to 14.45% in pentaploids. As to stomata anatomy, tetraploid genomic combinations showed smaller and more numerous stomata, as opposed to what was observed in pentaploids. The use of chromosome counting and flow cytometry was more effective than the anatomy of stomata for the characterization of genomic combinations. As to forage dry matter production, the HCM-5x-2 genomic combination outstood the pentaploids while the HCM-4x-2 outstood the tetraployds. The improvement of forage quality in Pennisetum through the introgression of favorable traits from millet was enhanced by the improvement of genomic pentaploids combinations peformance for bromatologic traits, showing their potential for being included in genetic breeding programs.
Aiming at contributing to the elephant grass improvement program of the Embrapa Gado de Leite, genomic combinations resulting from the backcrossing of hybrids with its parental hexaploid elephant grass and pearl millet were evaluated for cytogenetic, anatomical and agronomic/ bromatological characteristics. Pennisetum purpureum (2n = 4x = 28, genomes A'A'BB) and Pennisetum glaucum (2n = 2x = 14, genome AA) produce the triploid hybrid with genomic formation AA'B, gathering superior fodder characteristics from both parents. However it is sterile due to irregular pairing of chromosomes in meiosis. When antimitotic agents were used in order to double the chromosomes number, the hexaploid of genomic constitution AAA'A'BB is obtained. The AA'A'BB and AAA'B genomic combinations resulting from the backcrossing of hexaploid with elephant grass and hexaploid with pearl millet, respectively, showed a high degree of mixoploidy. The pentaploids chromosomes number ranged from 20 to 34, and the most frequent ones numbered 28. The tetraploids chromosomes number ranged from 16 to 28, and the most common ones numbered 21. More variation was noticed in the chromosomes number of the pentaploids genomic combinations than in those of tetraploids. Flow cytometry showed DNA loss in genomic combinations which ranged from 14.71 to 19.00% in tetraploids and from 9.25 to 14.45% in pentaploids. As to stomata anatomy, tetraploid genomic combinations showed smaller and more numerous stomata, as opposed to what was observed in pentaploids. The use of chromosome counting and flow cytometry was more effective than the anatomy of stomata for the characterization of genomic combinations. As to forage dry matter production, the HCM-5x-2 genomic combination outstood the pentaploids while the HCM-4x-2 outstood the tetraployds. The improvement of forage quality in Pennisetum through the introgression of favorable traits from millet was enhanced by the improvement of genomic pentaploids combinations peformance for bromatologic traits, showing their potential for being included in genetic breeding programs.
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Genética e Melhoramento de Plantas
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LEÃO, F. F. Citogenética e potencial forrageiro de combinações genômicas de capim-elefante e milheto. 2009. 112 p. Tese (Doutorado em Genética e Melhoramento de Plantas)-Universidade Federal de Lavras, Lavras, 2009.