Heterosis and Combining Ability of CIMMYT's Quality Protein Maize Germplasm: I. Lowland Tropical

Abstract

CIMMYT has developed a wide array of hard endosperm opaque‐2 (o2) maize (Zea mays L.) germplasm, through the combined use of two genetic systems involving the o2 gene for improving protein quality and the genetic modifiers of the o2 locus for improving kernel phenotype and ameliorating other o2‐associated defects. The objective of this study was to determine the heterotic patterns and combining ability of tropical quality protein maize (QPM) germplasm, and identify superior germplasm suitable for hybrid development. Ten parents (four QPM pools, five QPM populations, and experimental variety PR 7737) were used in a diallel study in eight environments. Data on grain yield, time to silk, plant height, and endosperm hardness were recorded. General combining ability (GCA) effects were highly significant for all traits; specific combining ability (SCA) effects were signififant for time to silk and plant height. Genotype × environment interactions and their partitions were significant for grain yield and endosperm hardness. Pool 24 QPM was the highest‐yielding parent (6.48 Mg ha‐1) and Pool 24 QPM × Population 63 was the highest‐yielding croos (6.56 Mg ha‐1) among hard endosperm parents. PR 7737, a soft endosperm opaque‐2, was low yielding as a parent, but performed better in crosses with other hard endosperm parents and showed high heterosis. High‐parent heterosis for grain yield was generally low in all crosses except those involving PR 7737 as a parent. Endosperm hardness ratings were intermediate relative to the parents, suggesting polygenic control. Crosses among white endosperm parents generally performed better than crosses among yellow endosperm parents. Crosses among dents and dent × flints yielded higher than flint crosses, but flint parents and their crosses had a superior endosperm modification. compared with dents. Populations 62, 63, and PR 7737 showed significant positive GCA effects for grain yield; Pool 23 QPM, Pool 25 QPM, and Populations 62, 64, and 65 had significant negative GCA effects for endosperm hardness. Populations 62 and 63 among white endosperm materials and Population 65 among yellow endosperm could be used for initiating hybrid development work. The broad genetic base provides opportunities for developing intrapopulation interline hybrids.

Heterotic Patterns of IITA and CIMMYT Early‐Maturing Yellow Maize Inbreds under Contrasting Environments

“…The significant GCA × E interaction suggested the need to select different parental lines for hybrid development under each environment and indicated that there was scope for the improvement of most traits through selection and hence a chance to identify a potentially discriminating tester. This result is in agreement with the findings of several workers (Gutierrez-Gaitan et al, 1986;Hallauer et al, 2010;Vasal et al, 1993;Badu-Apraku et al, 2004;Fan et al, 2009;Badu-Apraku et al, 2011a, 2011b, emphasizing the need for testing inbred lines in contrasting environments to identify those with stable performance for the development of drought tolerance. It is expected that testing lines under different environments should facilitate the selection of stable testers and hybrids (Scott, 1967;Badu-Apraku et al, 2013a).…”

Gene Action and Some Genetic Parameters for Grain Yield, Its Components and Growth Traits of Corn in Full Diallel Cross

“…The success of identifying such parents mainly depends on the gene action that controls the trait under improvement (Brown, 1960;Vasal et al, 1993;Wellhausen, 1965). Genetic diversity exploitation for any plant has been recognized as a potential source of new genes to increase the genetic variability and heterosis are referred to its breeding method and the genetic base (Goodman, 1985;Vasal et al, 1992).…”

“…Crossa and Gardner (1987) and Michelini (1991) indicated that populations with 25-50% exotic germplasm don't differ significantly for grain yield, and have greater genetic variability than adapted sources. Vasal et al (1992Vasal et al ( , 1993 provided maize breeders valuable information on the combining ability and heterotic patterns of CIMMYT's maize germplasm. The genetic basis and its utilization in breeding programs concentrated the evident about using some criteria of genetic distances (Fountain & Hallauer, 1996).…”

Tecnología y producción de semillas de híbridos y variedades sobresalientes de maíz de calidad proteínica (QPM) en México.

“…Los problemas son de volumen así como la calidad del grano de maíz. Una alternativa para aminorar la desnutrición y baja producción de maíz, son los llamados maíces de calidad proteínica (QPM: Quality Proteín Maize), los cuales fueron desarrollados a partir de los trabajos con maíz opaco 2 ( (Vasal et al 1980, Vasal et al 1993). El maíz QPM, tuvo su origen en el llamado Opaco 2.…”

“…Estos maíces ahora se conocen mundialmente, como Maíz de Calidad Proteínica (QPM). Estos genes modificadores confieren a el endospermo de variedades, líneas e híbridos una textura de grano más dura que el maíz opaco, dando la apariencia de un maíz común o normal (Vasal et al 1993, Vasal 1994. Los trabajos desarrollados por el Dr. Surindel Vasal y Dra.…”