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Combining ability studies have been extensively used to assess gene action responsible for various traits including disease resistance in maize. Some backcross (BC 3 F 2 ) and dihaploid (DH) lines developed through marker assisted selection have not been tested for their yield performances in hybrid combinations. A total of 16 BC 3 F 2 lines and their parental checks and 60 DH lines including lines and their parental checks were crossed to two single cross testers (CML312/CML442 and CML395/CML444) using Line x Tester design. The 152 three-way hybrids generated were evaluated for yield performance and other agronomic traits under artificial MLN inoculation, low nitrogen soil and optimum conditions in Kenya and South Sudan in 2019. Significant genotype, GxE, general combining ability (GCA) and specific combining ability (SCA) effects ( p ≤0.01) were detected for grain yield (t/ha) and maize lethal necrosis (MLN) scores. GCA effects were preponderant over SCA effects for most traits. High broad sense and moderate narrow sense heritability estimates for all traits across management options were detected. This implied that these traits could be improved through recurrent selection. DH lines D3, D14, D57 and BC 3 F 2 lines BCL3, BCL5, BCL8 showed desirable GCA effects for MLN resistance and grain yield. DH derived hybrids DH70, DH43, DH18 and DH40; and backcross (BC) derived hybrids BH28 and BH01 demonstrated desirable SCA effects for the same traits. Deployment of these MLN resistant lines into breeding programmes should result into improved MLN resistance and increased grain yields. The superior hybrids will provide desirable options for farmers who continue to experience low average maize yields due to MLN infections.

The objective of this work was to evaluate the alterations of antioxidant enzyme reserves and antioxidant enzymes during germination under water deficit in maize hybrids and to associate with seed vigor, determining the mechanisms related to tolerance for this stress. Two three-way maize hybrids were characterized by their vigor at different levels of water deficit induced by polyethylene glycol 6000. Next, the seeds were hydrated at different osmotic potentials (0.0, -0.3, and -0.9 MPa) and removed at different times to assess the levels of the total soluble protein, total soluble sugars, proline, starch, and antioxidant enzymes, such as superoxide dismutase, catalase and ascorbate peroxidase. The analysis of variance, Tukey test at 5% and principal component analysis (PCA) were used. The vigorous hybrid (HT1) was more efficient than the low vigor hybrid seeds (HT2) in mobilizing the total soluble protein during the initial stages of germination and the total soluble sugars before and after root protrusion under water deficit in addition to increasing the catalase activity at the different osmotic potentials that were assessed. The objective of this work was to evaluate the alterations of antioxidant enzyme reserves and antioxidant enzymes during germination under water deficit in maize hybrids and to associate with seed vigor, determining the mechanisms related to tolerance for this stress. Two three-way maize hybrids were characterized by their vigor at different levels of water deficit induced by polyethylene glycol 6000. Next, the seeds were hydrated at different osmotic potentials (0.0, -0.3, and -0.9 MPa) and removed at different times to assess the levels of the total soluble protein, total soluble sugars, proline, starch, and antioxidant enzymes, such as superoxide dismutase, catalase and ascorbate peroxidase. The analysis of variance, Tukey test at 5% and principal component analysis (PCA) were used. The vigorous hybrid (HT1) was more efficient than the low vigor hybrid seeds (HT2) in mobilizing the total soluble protein during the initial stages of germination and the total soluble sugars before and after root protrusion under water deficit in addition to increasing the catalase activity at the different osmotic potentials that were assessed.

En los programas de mejoramiento genético de maíz (Zea mays L.) y de generación de híbridos de la Facultad de Estudios Superiores Cuautitlán (FESC-UNAM) y del Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP-CEVAMEX), se emplean la esterilidad masculina y la incorporación de este carácter, en las líneas élites como una alternativa para facilitar la producción de semillas, favorecer el mantenimiento de la calidad genética, y disminuir costos de producción de semilla, al liberarse comercialmente para su uso extensivo y abastecimiento de semilla de nuevos híbridos. En estos programas, desde 1992, se trabaja con androesterilidad, contándose con híbridos trilíneales, para productores de maíz de los Valles Altos de México (2200 a 2600 msnm), cuyos progenitores tienen el carácter de androesterilidad. Con base en ello, se consideró necesario evaluar un grupo de híbridos trilíneales así como las cruzas simples progenitoras, para definir la estabilidad del rendimiento, y determinar la interacción genotipo x ambiente de los híbridos en diferentes ambientes de prueba, con el propósito de establecer una recomendación adecuada y apoyar su liberación comercial en ambientes específicos. Adicionalmente, para estos híbridos se tuvo como objetivos, en un trabajo paralelo, a) definir la capacidad productiva de estos híbridos trilíneales de maíz, en sus versiones androestéril y fértil; b) determinar la mejor proporción de mezcla de semilla androestéril (AE) y fértil (F), bajo dos densidades de población (50 000 y 70 000 plantas por hectárea); c) identificar a los híbridos trilineales y sus cruzas simples progenitoras que tuvieran mejor estabilidad del rendimiento de grano, utilizando para ello los Parámetros de Estabilidad de Eberhart y Russell, y el modelo AMMI, y d) definir al modelo que mejor describa la interacción genotipo por ambiente para poder lo recomendar la liberación comercial de los híbridos trilineales. En el análisis de varianza para rendimiento, se obtuvieron diferencias altamente significativas para ambientes, genotipos y densidades; en la interacción Genotipo x Ambiente resultó significativa. Los mejores rendimientos los tuvo el híbrido H-53, con 7438 kg ha-1; mientras que el ambiente con el mejor rendimiento fue Cuautitlán Izcalli en la segunda fecha de siembra. La mejor densidad de población fue 70 000 plantas por hectárea. Las proporciones de semilla 33%AE y 67%F, con 6290 kg ha-1; y 66%AE y 34%F con 6200 kg ha-1, fueron mejores que otras mezclas de semilla androestéril y fértil y que la versión 100% fértil. En la parte de la evaluación de la estabilidad y la interacción genotipo x ambiente, el modelo AMMI identificó como estables a los híbridos trilineales H-57 y Puma 1183 AEC2, así como a las cruzas simples H-57 AE y H-57 F; en cuanto a los parámetros de estabilidad los híbridos trilineales H-53, Puma 1183 AEC1 y Puma 1183 AEC2, y las cruzas simples H-57 AE, Puma 1183 AEC1 AE, y Puma 1183 AEC1 F resultaron estables. Los niveles de correspondencia entre ambos modelos, para los híbridos trilineales y las cruzas simples, fue del 50% y 20%, respectivamente. Ambos modelos identificaron por lo menos a un híbrido trilineal y una cruza simple, como estable. Se concluye que el modelo AMMI describió mejor la interacción genotipo por ambiente. _______________ GRAIN AND SEED PRODUCTIVITY OF SINGLE AND THREE-WAY AND SINGLE CROSSES OF ANDROESTERILE AND FERTILE MAIZE. ABSTRACT: The maize (Zea mays l.) breeding project and the hibrid development program the Faculty of Superior Studies Cuautitlan (FESC-UNAM) and the National Institute for Forestry, Agricultural and Animal Research (CEVAMEX-INIFAP) uses the male sterility system for the incorporation of this character to the elite inbred lines. This alternative facilitates the production of seed and also favored the maintenance of the genetic quality and lowered the cost of seed production on commerciall maize released for extensive use and for seed supplying of new hybrids. Since 1992, the project has developed tree-way hybrids to be grown by maize farmers for the High Valleys of Mexico (2200-2600 meters above sea level), whose parents have the character of male sterility. Based on this, it was necessary to assess a group of three-way maize hybrids as well as single crosses in order to study their yield stability, and genotype x environment interaction of hybrids across different test environments to establish a proper recommendation and to support their commercial release to specific environments. Other objective of this work were: a) to study the productivity potencial of the androsterile an fertile versions of the hybrids; b) to determine the best proportion of male-sterile (MS) and fertile (F) seed mixtures, under two plant densities (50 000 and 70 000 plants per hectare); c) to identify the best hybrids and their progenitor single crosses with de best grain yield stability by means of the Eberhart and Russell´s parameters of stability, and the AMMI model, and d) to define the model that best describes the genotype by environment interaction, allowing to recommend the commercial release of the three-way maize hybrids. For the analysis of variance for yield, there were highly significant differences among environments, genotypes and densities for grain yield and that the genotype x environment interaction was significant. The hybrid H-53 had the highest yield, 7438 kg ha-1, and the best environment was Cuautitlán Izcalli in the second planting date. The best population density was 70,000 plants per hectare. The best mix proportions of seed were 33% MS and 67 %F, with 6,290 kg ha-1; and the mix of 66% MS and 34 %F, with 6,200 kg ha-1. For the evaluation of the stability and genotype x environment interaction, the model AMMI identified to the three-way Hybrids H-57 and Puma 1183 AEC2, and the single crosses H-57 AE and H-57 F, as the stablest ones. Considering the stability parameters, the three-way hybrids H-53, Puma 1183 1183 AEC1 and Puma AEC2, and the single crosses H-57 AE, 1183 AEC1, AE and Puma 1183 F AEC1 were considered as stables. The levels of correspondence between the two models, for the three-way hybrids and the single crosses were 50% and 20%, respectively. Both models al least identified one three-way and one single cross hybrid as stable. It is concluded that the AMMI model described better the genotype by environment interaction.