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• An. Esc. Super. Agric. Luiz de Queiroz 2 • 1945 • https://doi.org/10.1590/S0071-12761945000100007   copiar

Estudos genéticos sôbre o milho tunicata

Autoria SCIMAGO INSTITUTIONS RANKINGS

Resumo

The study of pod corn seems still of much importance from different points of view. The phylogenetical importance of the tunicate factor as a wild type relic gene has been recently discussed in much detail by MANGELSDORF and REEVES (1939), and by BRIEGER (1943, 1944a e b). Selection experiments have shown that the pleiotropic effect of the Tu factor can be modified very extensively (BRIEGER 1944a) and some of the forms thus obtained permitt comparison of male and female inflorescences in corn and related grasses. A detailed discussion of the botanical aspect shall be given shortly. The genetic apect, finally, is the subject of the present publication. Pod corn has been obtained twice: São Paulo Pod Corn and Bolivia Pod Corn. The former came from one half ear left in our laboratory by a student and belongs to the type of corn cultivated in the State of São Paulo, while the other belongs to the Andean group, and has been received both through Dr. CARDENAS, President of the University at Cochabamba, Bolivia, and through Dr. H. C. CUTLER, Harvard University, who collected material in the Andes. The results of the studies may be summarized as follows: 1) In both cases, pod corn is characterized by the presence of a dominant Tu factor, localized in the fourth chromosome and linked with sul. The crossover value differs somewhat from the mean value of 29% given by EMERSON, BEADLE and FRAZER (1935) and was 25% in 1217 plants for São Paulo Pod Corn and 36,5% in 345 plants for Bolivia Pod Corn. However not much importance should be attributed to the quantitative differences. 2) Segregation was completely normal in Bolivia Pod Corn while São Paulo Pod Corn proved to be heterozygous for a new com uma eliminação forte, funcionam apenas 8% em vez de 50%. Existem cerca de 30% de "jcrossing-over entre o gen doce (Su/su) e o fator gametofítico; è cerca de 5% entre o gen Tu e o fator gametofítico. A ordem dos gens no cromosômio IV é: Ga4 - Tu - Sul. 3) Using BRIEGER'S formulas (1930, 1937a, 1937b) the following determinations were made. a) the elimination of ga4 pollen tubes may be strong or weak. In the former case only about 8% and in the latter 37% of ga4 pollen tubes function, instead of the 50% expected in normal heterozygotes. b) There is about 30,4% crossing-over between sul and ga4 and 5,3% between Tu and ga3, the order of the factors beeing Su 1 - Tu - Ga4. 4) The new gametophyte factor differs from the two others factors in the same chromosome, causing competition between pollen tubes. The factor Gal, ocupies another locus, considerably to the left of Sul (EMERSON, BEADLE AND FRAZSER, 1935). The gen spl ocupies another locus and causes a difference of the size of the pollen grains, besides an elimination of pollen tubes, while no such differences were observed in the case of the new factor Ga4. 5) It may be mentioned, without entering into a detailed discussion, that it seems remarquable that three of the few gametophyte factors, so far studied in detail are localized in chromosome four. Actuality there are a few more known (BRIEGER, TIDBURY AND TSENG 1938), but only one other has been localized so far, Ga2, in chromosome five between btl and prl. (BRIEGER, 1935). 6) The fourth chromosome of corn seems to contain other pecularities still. MANGELSDORF AND REEVES (1939) concluded that it carries two translocations from Tripsacum chromosomes, and BRIEGER (1944b) suggested that the tu allel may have been introduced from a tripsacoid ancestor in substitution of the wild type gene Tu at the beginning of domestication. Serious disturbances in the segregation of fourth chromosome factors have been observed (BRIEGER, unpublished) in the hybrids of Brazilian corn and Mexican teosinte, caused by gametophytic and possibly zygotic elimination. Future studies must show wether there is any relation between the frequency of factors, causing gametophyte elimination and the presence of regions of chromosomes, tranfered either from Tripsacum or a related species, by translocation or crossing-over.

Estudos genéticos sôbre o milho tunicata (* (* ) Recebido para publicação em 13-IX-1945. )

F. G. Brieger

Escola Superior de Agricultura "Luiz de Queiroz", Universidade de S. Paulo

ABSTRACT

The study of pod corn seems still of much importance from different points of view. The phylogenetical importance of the tunicate factor as a wild type relic gene has been recently discussed in much detail by MANGELSDORF and REEVES (1939), and by BRIEGER (1943, 1944a e b). Selection experiments have shown that the pleiotropic effect of the Tu factor can be modified very extensively (BRIEGER 1944a) and some of the forms thus obtained permitt comparison of male and female inflorescences in corn and related grasses. A detailed discussion of the botanical aspect shall be given shortly. The genetic apect, finally, is the subject of the present publication.

Pod corn has been obtained twice: São Paulo Pod Corn and Bolivia Pod Corn. The former came from one half ear left in our laboratory by a student and belongs to the type of corn cultivated in the State of São Paulo, while the other belongs to the Andean group, and has been received both through Dr. CARDENAS, President of the University at Cochabamba, Bolivia, and through Dr. H. C. CUTLER, Harvard University, who collected material in the Andes.

The results of the studies may be summarized as follows:

1) In both cases, pod corn is characterized by the presence of a dominant Tu factor, localized in the fourth chromosome and linked with sul. The crossover value differs somewhat from the mean value of 29% given by EMERSON, BEADLE and FRAZER (1935) and was 25% in 1217 plants for São Paulo Pod Corn and 36,5% in 345 plants for Bolivia Pod Corn. However not much importance should be attributed to the quantitative differences.

2) Segregation was completely normal in Bolivia Pod Corn while São Paulo Pod Corn proved to be heterozygous for a new com uma eliminação forte, funcionam apenas 8% em vez de 50%. Existem cerca de 30% de "jcrossing-over entre o gen doce (Su/su) e o fator gametofítico; è cerca de 5% entre o gen Tu e o fator gametofítico. A ordem dos gens no cromosômio IV é: Ga4 - Tu - Sul.

3) Using BRIEGER'S formulas (1930, 1937a, 1937b) the following determinations were made.

a) the elimination of ga4 pollen tubes may be strong or weak. In the former case only about 8% and in the latter 37% of ga4 pollen tubes function, instead of the 50% expected in normal heterozygotes.

b) There is about 30,4% crossing-over between sul and ga4 and 5,3% between Tu and ga3, the order of the factors beeing Su 1 - Tu - Ga4.

4) The new gametophyte factor differs from the two others factors in the same chromosome, causing competition between pollen tubes. The factor Gal, ocupies another locus, considerably to the left of Sul (EMERSON, BEADLE AND FRAZSER, 1935). The gen spl ocupies another locus and causes a difference of the size of the pollen grains, besides an elimination of pollen tubes, while no such differences were observed in the case of the new factor Ga4.

5) It may be mentioned, without entering into a detailed discussion, that it seems remarquable that three of the few gametophyte factors, so far studied in detail are localized in chromosome four. Actuality there are a few more known (BRIEGER, TIDBURY AND TSENG 1938), but only one other has been localized so far, Ga2, in chromosome five between btl and prl. (BRIEGER, 1935).

6) The fourth chromosome of corn seems to contain other pecularities still. MANGELSDORF AND REEVES (1939) concluded that it carries two translocations from Tripsacum chromosomes, and BRIEGER (1944b) suggested that the tu allel may have been introduced from a tripsacoid ancestor in substitution of the wild type gene Tu at the beginning of domestication. Serious disturbances in the segregation of fourth chromosome factors have been observed (BRIEGER, unpublished) in the hybrids of Brazilian corn and Mexican teosinte, caused by gametophytic and possibly zygotic elimination.

Future studies must show wether there is any relation between the frequency of factors, causing gametophyte elimination and the presence of regions of chromosomes, tranfered either from Tripsacum or a related species, by translocation or crossing-over.

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LITERATURA

  • 1 - BRIEGER, F. G. 1930 - Selbsterilität und Krekzgunugs sterilität. Berlin. Springer, 395 pg.
  • 2 - BRIEGER, F. G. 1937a - Genetic control of gametophyte development in maize I A gametophyte factor in chromosome five. Journal of Genetics. 34: 58-80.
  • 3 - BRIEGER F. G. 1937b - Methoden der Erforschung der Verebungs vorgänge bei Pflanzen. Handbuchbiol. Arbeitsmetoden. (Abderhalden). IX 3: 1183-1308.
  • 4 BRIEGER, F. G. 1043 - Origem do milho. Semana da Genética. Rev. Agr. 16: 409-418.
  • 5 - BRIEGER, F. G. 1944a - Considerações sôbre o mecanismo da evolução. Anais da Escola Sup. Agr. "Luiz de Queiroz". 1: 177-211.
  • 6 - BRIEGER, F. G. 1944b - Estudos experimentais sôbre a origem do milho. Anais da Esc. Sup. Agr. "Luiz de Queiroz". 1: 225-278.
  • 7 - BRIEGER, F. G. 1945 - A ação de gens gametofíticos, com referência especial ao milho. Anais da Esc. Sup. Agr. "Luiz de Queiroz". 2. (em impressão).
  • 8 - BRIEGER, F. G., E. TIDBURY AND H. P. TSENG. 1938 - Genetic control of gametophyte develpment in maize. II The Quarter test. Journal of Gentics, 36: 17-38.
  • 9 - COLLINS, G. N. 1917a. - Hybrids of Zea ramosa and Zea tunicata. Jour. Agr. Res. 9: 383-395.
  • 10 - COLLINS, G. N. 1917a. - Hybrids of Zea tunicata and Zea ramosa. Nat. Acad. Sc. Proc. (U.S.A.) 3: 345-349.
  • 11 - EMERSON, R. A., G. W. BEADLE and A. C. FRASER 1935 - A summary of linkage studies in maize. Cornell Univ. Agr. Exp. Sta. 180: 83 pgs.
  • 12 - EYSTER, W. H. 1934 - The genetics of Zea Mays. Bibl. Gen. 11: 187-392.
  • 13 - HOROWITZ, S., A. H. MARCHONI y H. G. FISHER 1943 - El factor Sux y el aumento del contenido de azucar en el maiz para choclo. An. Inst. Fitotecnico. Santa Catalina. 3: 37-44.
  • 14 - MANGELSDORF, P. C. and R. G. REEVES 1939 - The origin of indian corn and its relatives. Texas Agr. Sta. 574: 315 pg.
  • 15 - MATSUURA, H. 1933 - A bibliographical monograph on plant genetics. 787 pg.
  • 16 - SAINT-HILAIRE, A. de, 1829 - Letre sur une varieté remarquable de maiz du Bresil. An. Sc. Nat. Paris. 16: 143-145.
  • (*
    ) Recebido para publicação em 13-IX-1945.

    • Datas de Publicação

    • Publicação nesta coleção
      25 Fev 2013
    • Data do Fascículo
      1945

    Histórico

    • Recebido
      12 Set 1945
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