Resumo
The experiments reported were started as early as 1933, when indications were found in class material that the factor for small pollen, spl, causes not only differences in the size of pollen grains and in the growth of pollen tubes, but also a competition between megaspores, as first observed by RENNER (1921) in Oenothera. Dr. P. C. MANGELSDORF, who had kindly furnished the original seeds, was informed and the final publication delayed untill his publication in 1940. A further delay was caused by other circunstances. The main reason for the differences of the results obtained by SINGLETON and MANGELSDORF (1940) and those reported here, seems to be the way the material was analysed. I applied methods of a detailed statistical analysis, while MANGELSDORF and SINGLETON analysed pooled data. 1) The data obtained on pollen tube competition indicate .that there is about 3-4% of crossing-over between the su and sp factors in chromosome IV. The elimination is not always complete, but from 0 to 10% of the sp pollen tubes may function, instead of the 50% expected without elimination. These results are, as a whole, in accordance with SINGLETON and MANGELSDORF's data. 2) Female elimination is weaker and transmission determined as between 16 to 49,5%, instead of 50% without competition, the values being calculated by a special formula. 3) The variability of female elimination is partially genotypical, partially phenotypical. The former was shown by the difference in the behavior of the two progenies tested, while the latter was very evident when comparing the upper and lower halves of ears. For some unknown physiological reason, the elimination is generally stronger in the upper than in the lower half of the ear. 4) The female elimination of the sp gene may be caused theoretically, by either of two processes: a simple lethal effect in the female gametophyte or a competition between megaspores. The former would lead not only to the abortion of the individual megaspores, but of the whole uniovulate ovary. In the case of the latter, the abortive megaspore carrying the gene sp will be substituted in each ovule by one of the Sp megaspores and no abortion of ovaries may be observed. My observations are completely in favor of the second explication: a) The ears were as a whole very well filled except for a few incomplete ears which always appear in artificial pollinations. b) Row arrangement was always very regular. c) The number of kernels on ears with elimination is not smaller than in normal ears, but is incidentally higher : with elimnation, in back-crosses 354 kernels and in selfed ears 390 kernels, without elimination 310 kernels per ear. d) There is no correlation between the intensity of elimination and the number of grains in individual ears; the coefficient; of linear correlation, equal to 0,24, is small and insignificant. e) Our results are in complete disagreement whit those reported by SINGLETON and MANGELSDORF (1940). Since these authors present only pooled date, a complete and detailed analysis which may explain the cause of these divergences is impossible.
Competição entre megaspórios em milho (* (* ) Recebido para publicação em 13-IX-1945. )
F. G. Brieger
Escola Superior de Agricultura "Luiz de Queiroz", Universidade de S. Paulo
ABSTRACT
The experiments reported were started as early as 1933, when indications were found in class material that the factor for small pollen, spl, causes not only differences in the size of pollen grains and in the growth of pollen tubes, but also a competition between megaspores, as first observed by RENNER (1921) in Oenothera. Dr. P. C. MANGELSDORF, who had kindly furnished the original seeds, was informed and the final publication delayed untill his publication in 1940. A further delay was caused by other circunstances.
The main reason for the differences of the results obtained by SINGLETON and MANGELSDORF (1940) and those reported here, seems to be the way the material was analysed. I applied methods of a detailed statistical analysis, while MANGELSDORF and SINGLETON analysed pooled data.
1) The data obtained on pollen tube competition indicate .that there is about 3-4% of crossing-over between the su and sp factors in chromosome IV. The elimination is not always complete, but from 0 to 10% of the sp pollen tubes may function, instead of the 50% expected without elimination. These results are, as a whole, in accordance with SINGLETON and MANGELSDORF's data.
2) Female elimination is weaker and transmission determined as between 16 to 49,5%, instead of 50% without competition, the values being calculated by a special formula.
3) The variability of female elimination is partially genotypical, partially phenotypical. The former was shown by the difference in the behavior of the two progenies tested, while the latter was very evident when comparing the upper and lower halves of ears. For some unknown physiological reason, the elimination is generally stronger in the upper than in the lower half of the ear.
4) The female elimination of the sp gene may be caused theoretically, by either of two processes: a simple lethal effect in the female gametophyte or a competition between megaspores. The former would lead not only to the abortion of the individual megaspores, but of the whole uniovulate ovary. In the case of the latter, the abortive megaspore carrying the gene sp will be substituted in each ovule by one of the Sp megaspores and no abortion of ovaries may be observed. My observations are completely in favor of the second explication:
a) The ears were as a whole very well filled except for a few incomplete ears which always appear in artificial pollinations.
b) Row arrangement was always very regular.
c) The number of kernels on ears with elimination is not smaller than in normal ears, but is incidentally higher : with elimnation, in back-crosses 354 kernels and in selfed ears 390 kernels, without elimination 310 kernels per ear.
d) There is no correlation between the intensity of elimination and the number of grains in individual ears; the coefficient; of linear correlation, equal to 0,24, is small and insignificant.
e) Our results are in complete disagreement whit those reported by SINGLETON and MANGELSDORF (1940). Since these authors present only pooled date, a complete and detailed analysis which may explain the cause of these divergences is impossible.
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LITERATURA
- 1 - BRÍEGER, F. G. 1930 - Selbsterilitãt and Kreuzungs- sterilität. Berlin. Springer, 395 pg.
- 2 - BRIEGER F. G. 1937a - Methoden der Erforschung der Vererbungs-vorgange. Handbuch Biol. Methoden (Abderhalden) 1X3: 1183-1308.
- 3 - BRIEGER, F. G. 1937b - Genetic controll of gametophy- te development in maize I. A gametophyte factor in chromosome five. Journal of Genetics. 34: 57-80.
- 4 - BRIEGER, F. G. 1945a - A ação dos gens gametofíticos, com referência especial ao milho. Anais da Escola Agr. "Luiz de Queiroz" 2:.261 -
- 5 - BRIEGER, F. G. 1945b - Estudos genéticos sobre o mi- lho tunicata. Anais da Escola Agr. "Luiz de Queiroz" 2:.
- 6 - MANGELSDORF, P. C. 1928 - The effect of a lethal on the heteroziygote in maize. Journal of Heredity, 19 : 123-13.1
- 7 - MANGELSDORF, P. C. 1931 - Modification of mende- lian ratios in maize by mechanical separation of gametes. Proc. Nat. Acad. Sc. (U.S.A.). 17: 698-700.
- 8 - MANGELSDORF, P. C. 1932 - Mechanical separation of gametes in maize. Journal of Heredity. 23: 289-295.
- 9 - RENNER, O. 1921 - Heterogamie im weiblichen Ges- chlecht und Embroyosackentwicklung bei den Oenotheren. Zeitschrift f. Bot. 13 : 609-621.
- 10 - RHOADES, M. M. 1942 - Preferential segregation in maize. Genetics. 27:395-407.
- 11 - SINGLETON, W. R. 1932 - Complete elimination of certain classes of gametes in Zea. Proc. 6th. Inter. Congress. Genetics. 2: 182-184.
- 12 - SINGLETON, W. R. 1940 - Influence of female stock on the functioning of small pollen and male gametes. Proc. Nac. Acad. Sc. (U.S.A.). 26: 102-104.
- 13 - SINGLETON, W. R. AND P. C. MANGELSDORF. 1940 - Gametic lethals on the fourth chromosome of maize. Genetics. 25: 366-390.
Datas de Publicação
-
Publicação nesta coleção
25 Fev 2013 -
Data do Fascículo
1945
Histórico
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Recebido
13 Set 1945
