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An improved procedure for testing theoretical segregation models in qualitative genetic studies of soybeans

Carlos A. Arrabal Arias; José F. Ferraz de Toledo; José Tadashi Yorinori

Empresa Brasileira de Pesquisa Agropecuária, EMBRAPA, CNPSo, Rodovia Carlos João Strass, Acesso Orlando Amaral, Distrito de Warta, Caixa Postal 1061, 86001-970 Londrina, PR, Brasil. Send correspondence to C.A.A.A.

ABSTRACT

A procedure to study simply inherited traits is proposed. It consists of a chi-square test, where the theoretical expected frequencies for the F2 generation are calculated based on the observed distribution of parents and F1, together with the theoretical hypothesis for segregation ratios, taking into consideration possible overlapping between phenotypic classes. A single splitting point is used to limit the phenotypic classes, regardless of the cross being studied. The procedure is shown to complement well the mean and variance analyses inherent of a quantitative genetics approach.
Three crosses of a study on the inheritance of resistance of soybeans (Glycine max L. Merrill) to race Cs-15 of Cercospora sojina (frog-eye leaf spot) were chosen to illustrate our procedure. Qualitative and quantitative analyses were performed on mean and variance data. Estimates of mean components and scaling tests helped to interpret qualitative analyses made by the modified chi-square test.
Comparisons with conventional analysis were made. The improved method is useful for research involving simple genetic inheritance of environmentally susceptible characters. In spite of environmental interference and the absence of dominance in some crosses, which makes interpretation of segregation patterns more difficult, one main locus for resistance was observed among the cultivars. The results suggest that the study of inheritance of resistance to C. sojina must be done near or at the V5 growth stages of soybean.

Keywords: segregation models; qualitative genetic; soybeans.

REFERENCES

Arias, C.A.A. (1991). Herança da resistência da soja (Glycine max) às raças 4 e 15 de Cercospora sojina. Master's Thesis, Universidade Estaduald e Londrina, Londrina, PR, Brasil.

Fehr, W.R., Caviness, C.E., Burmood, D.T. and Pennington, J.S. (1971). Stage of development descriptions for soybeans (Glycine max). Crop. Sci. 11: 929-931.

Mather, K. and Jinks, J.L. (1982). Biometrical Genetics: the Study of Continuous Variation. 2nd edn. Cornell University Press, Ithaca, pp. 382.

Yorinori, J.T. (1980). Cercospora sojina: pathogenicity, new races and seed transmission in soybean. Doctoral Thesis, University of Illinois, Urbana-Champaign, U.S.A.

Yorinori, J.T. (1982). Identificação de raças de Cercospora sojina Ham a nível nacional. In: Resultados de Pesquisa de Soja 1981/82. Empresa Brasileira de Pesquisa Agropecuária; Centro Nacional de Pesquisa de Soja, Londrina, pp. 234-235.

Yorinori, J.T. (1989). Frogeye leaf spot of soybean (Cercospora sojina Ham). In: World Soybean Research Conference -IV. Buenos Aires, Argentina, March 5-9. Vol. III.