El cultivo de maíz en México es el más importante debido a la superficie sembrada, valor de la producción, por ser el alimento principal de la población y por ocupar el 20% de la población económicamente activa. Durante 1998, se sembraron a nivel nacional 7,9 millones de hectáreas con un rendimiento medio de 2,3 t/ha y una

Economic indexes for the production and use of improved corn of quality protein (QPM) in Mexico. To promote the extensive use of quality protein corns (QPM), schemes as kg/kg of corn could be an alternative to support its spreading. The Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP) in coordination with the CIMMYT, intensified research projects which allowed the releasing of commercial hybrids and QPM corn varieties. However, joint to the characteristics of each one of the materials, it is convenient to analyze the economic implications of the use of these seeds, based on their conformation as simple hybrids, trilineal, varietals, open-pollinated varieties, because there is a potential problem of its productive capacity and quality of progeny lines; which makes it necessary to analyze the efficiency of producing hybrid seeds. This work analyzes the impact of the productivity of each progenitor on the cost of producing mexican hybrids, based on the minimum productivity level. Also, an estimate is shown of the prices the farmers are willing to pay for the improved seed of quality protein varieties.

During the rainy season in 1998/98 a reseach was conducted in Campo Experimental Cotaxtla, Veracruz, México, with the objectives of knowing the response of five corn genotypes to doses fertilizer and plant density. A completed randomized block experimental design with two replications was used arranged in split plots where the genotypes (G) VS-536, H-512, H-513, HTV1 and HTV2 were considered as small plots ; The medium plots were doses of fertilization (F) of N2,P2O5,K2O: 161-46-0, 184-69-0, 184-69-30, 207-92-0 and 207-92-30 ; and the big plots were plant densities(D): 50, 62.5, 75, 93.75, 100 and 125 thousand plants/hectare. The characteristics studied were: harvest index, ears per plant, and grain yield. The analysis of variance showed significant differences for some characteristics in D, F, DxF y DxG and for all in G. According to this, the best genotype was the experimental hybrid HTV1 with yield 6.74 t/ha. The response to fertilization was only of to harvest index, where the best dose was 184-69-0. In relation with plant density, with 62500 plants/hectare, all genotypes showed their best yield and number of ears per plant.

Thus, during autumn - winter season in 1996/97, there were evaluated in Cotaxtla, Ver. top crosses of tropical maize lines derived of several sources of germplasm such as: a) Recycled lines from H-513XVS-536, b) lines derived from a compound of wide genetic base (CABG3), c) Elite lines from Cotaxtla maize program and d) CIMMYT lines . There were used as testers, the lines LT154, and LT155 which are parents of H-513 and CML247 and CML254 which cross is an heterotic pattern defined by CIMMYT for the tropic . There were found lines like F31 x F30-4-3, F41 x F40-1-2, CABG3’-12-2-1-2-1, LT-174 y CML55 that registered good specific combining ability with tester 2 (LT-155) ;and F4 x F3-5-2 and CML15,with tester 4 (CML 254). On the other hand F4 x F5-5-1, CABG3’-12-2-1- 2-1, LT-174, CML13 and CML 15 had the best general combining ability. In relation with testers, it was found for recycled lines, that testers LT154 and CML254 registered the highest values for regression coefficients; It indicates that these testers identify the best lines; In lines derived from CABG3, tester LT155 registered the best value; In Elite lines, testers 2(LT155) and 3(CML247) identified better lines and from CIMMYT lines the best tester was CML254.

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