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KRUG, C. A.; VIEGAS, G. P.  and  PAOLIERI, L.. Híbridos comerciais de milho. Bragantia [online]. 1943, vol.3, n.11, pp.367-552. ISSN 0006-8705.

In the present bulletin the authors present the details of a 10 year's corn improvement project to produce hybrid varieties, which has been conducted by the Genetics Division of the Instituto Agronômico, Campinas, S. P., Brasil. A general description is given of the basic material which has been used ; the various methods of isolating and selecting pure lines, methods of hybridization and of the study of hybrids are described. In the main chapter the details of the breeding work is outlined, year by year general comments of the results obtained always being added. For the isolation of pure lines a total of 17 varieties, several hybrids and other types were used, more than 26.000 artificial selfings having been made. An attempt has also been made to adapt lines introduced from other countries, mainly from the United States of America. The selection of pure lines has been based on their morphological characters as well as on their combining ability (general and specific) which was determined by top-crosses with open pollinated varieties and whith other lines. That way it was succeeded to isolate lines with good vegetative characters and producing high yielding hybrids. Up to 1941-42 more than 3.700 hybrids were studied in a total of 47 field trials (single, three-way, double and inter-varietal crosses), of which 133 (3,5%), yielded significantly higher than the control varieties at Campinas, Ribeirão Preto and Pindorama, three different ecological zones in the State of São Paulo. The differences in yield varied between 7 and 92%, most of the hybrids being of the yellow flint type. Some of these hybrids showed significant higher yields at the three above mentioned regions and during two to three years. It is concluded that the preliminary part of the project has now come to an end and steps are taken to produce hybrid corn seeds on a commercial scale.

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