Abstract
A field experiment was conducted at the experimental farm of Field Crop Sciences Department, College of Agriculture / University of Baghdad. Five maize (Zea mays L.) inbred lines were tested for general and specific combining ability by using full diallel cross. Seed of inbred were planted in spring and fall season of 2013. In first season, seeds were planted, and at anthesis crossing between inbreds were done. In the fall season varietal trial for crosses and parents were conducted by using RCBD design with four replications to evaluate crosses and parents and to estimate some genetic parameters. Statistical analysis revealed high significant increases for all traits, ear height, leaves area, no of ears/plant, no. of grain/plant, grain weight, dry weight/plant and yield t/ ha. The genetic analysis showed that inbred 2 was superior and gave high grain yield (5.74 t/ha.), due to its high dry weight (207.82g/plant), and no. of grain /plant (704.49). In addition, it had positive GCA. The reciprocity cross 4×1 was superior and gave highest yield 6.98 t/ha. due to superiority in 100 grain weight (18.53g). It also had positive and higher hybrid vigor (45%) for grain yield, and positive effect of sca (1.56). All reciprocity crosses were higher than crosses; the highest one is 4 × 3, which gave 8.69 t/ha. All parent and crosses had had positive variance for yield, but all reciprocity crosses were negative. Mean square for SCA and RCA were more than GCA, and therefore the σ2 GCA was less which made σ2 A less than σ2D and σ2 Dr, so σ2 GCA / σ2 SCA and σ2 GCA / σ2 RCA became less than one and the degree of dominance was more than one, making h2 n.s very little. Thus, the trait was governed by non-additive gene action. We can conclude that there is a possibility of using superior inbreds to produce hybrids or use selection for it and produce synthetic varieties.
Highlights
The effective method for high yield selection requires information about the amount of genetic variation found in the population that is called combining ability and heterosis
General and specific combining ability were estimated according to Griffing [9], diallel cross analysis designated as first method, Fixed model, mathematicalmodel for crosses and reciprocal crosses are: Yijk = μ + gi + gj + Sij + Rik + eijk
Where yijk = the value of genotype ij in replicate k μ = overall average to row gi = effect of ability parent i Sij = effect of specific combining ability for singles cross-ij Rij = effect of specific combining ability for singles reciprocal cross ij eijk =modified experimental error effect The variance of general combining ability ∂2gca, and specific combining ability ∂2sca and variance of the reciprocal effect ∂2rca were calculated according to the following equations:
Summary
The effective method for high yield selection requires information about the amount of genetic variation found in the population that is called combining ability and heterosis. The selection of the superior parents for crossing and hybrid production is very important in breeding and improvement program, so that performance of hybrid related to the general and specific ability of inbreds within the a crossing. Crossing between genetically unrelated parents, at least one of them has a high General Combining Ability (GCA), will produce the superior hybrid [1] To achieve this goal diallel mating system used, which is progeny performance analysis that can be statistically partitioned to GCA and Specific Combining Ability (SCA) components, which are considered as an important means in identified the best crosses to exploitation hybrid vigor and choose the best crosses to be used as an improved varieties, or used in another breeding programs. Search aimed to understand the foundations of heterosis and how to investment it in efficient and precise the estimate of breeding values and the possibility of its investment in the crosses production which possess high SCA in its behavior and performance to increase the efficiency of traits improvement in maize
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