The objective of present study was to compare of several methods for estimating the degree of heritability and calculating the number of genes using generation mean analysis of maize (Zea mays L.). The experiment was conducted at the field of Field Crop Dept. College of Agric / Univ. of Baghdad, for many seasons, spring and fall seasons 2009, 2010, spring 2011 and fall 2013.Six diverse inbred lines were crossed to produce F1,F2,BC1 and BC2 for four superior crosses.Broad-sense and narrow sense heritability estimates based on variance of different generations. The results showed that the four formulas used to estimate the heritability were different in estimating the values of heritability of different traits, as well as the different crosses used in the study. The broad sense heritability was differed according to the components of the formulas used to estimate. The number of genes that controlled the trait differed according to the different method of estimation and according to the studied trait, and to the all crosses. The highest number of genes (for all formulas) for plant yield, ranging from 15.85 (cross 4) to 155.7 (cross 2), because the yield is complex quantitative trait of several components, so the number of genes they control are the sum of genes that control the components. The inbreeding depression differed according to the parents involved in the crosses, and according to the studied trait, the inbreeding depression ranged from -7 for number of branches/tassel of cross 1 and leaf area of cross 3 to 68 for grain yield of cross 2. We can conclude that the best formula to estimate heritability depends on experimental design and methods of breeding.
Correlation and path coefficient analysis were worked out for ten morphological traits in 30 three-way crosses of maize. Phenotypic and genotypic correlation analysis indicated that ear length; row numbers per ear, grain numbers per row, leaf area and leaves numbers had a positive significant correlation with grain yield per plant. Further partitioning of correlation coefficients into direct and indirect effects showed that traits days to silking, row numbers per row and leaves numbers had a positive direct effect on grain yield per plant. The traits ear length, grain numbers per row and leaf area had a maximum total effect on grain yield. Furthermore, PCA analysis has gave interested results and it supported the results of correlation and path analysis. The correlation and path analysis obviously indicated that direct selection based on these attributes may be useful in raising grain yield in maize.
Tension caused by a lack of water (water stress or drought stress) represents the continuous and continuous threat to the survival of the plant, as many of the plants in which phenotypic or physiological modification takes place may not be able to continue and remain in the environment in which they live due to the water stress on it or the low soil moisture content. This of course is related to the prevailing weather conditions (lack of rain, high temperature, increased wind speed, low relative humidity in the atmosphere … etc.), so dry soil is defined as the shortage of soil water needed to the extent that its readiness for the plant decreases (that is, the threshold at which the plant cannot absorb Or drain the water at a speed that meets its requirements for vital activities, and photosynthesis that meets the requirements of evapotranspiration does not occur. Conversely, water tightening may be the result of increased water. An example of stretching as a result of increased water is flooding, which results in suffocation resulting from Reduced concentration of oxygen-prepared oxygen to the roots, which in turn will impair breathing. In general, tension due to a lack of water is the most common, which led specialists to call it “water deficit stress.” Because water tension occurs in natural environments as a result of rain entrapping, Such conditions are known as drought conditions and therefore drought stress is terme In laboratory conditions, water stress conditions can be achieved through the loss of water by transpiration from the leaves, a circumstance that is due to what is termed as a desiccation stress. That is, in the sense that water stress is one of the components of salt tension and osmotic tension, and in order to unify these differences according to the concept of water tension, it termed the concept of low water potential.
"To evaluate the performance of introduced varieties of maize under different sowing dates and locations, in addition to local variety, a field experiment was carried out in two locations;. The study compared five varieties of maize introduced from America, with a local synthetic variety (Ibba 5018) and tested it in two locations at three sowing dates (1, 15 July and 1 August). The Randomized Complete Block Design RCBD was used with four replications, with spilt plot arrangements, the main plots included three sowing dates, the secondary plots included, the varieties. The traits of the days number to tassling and days to silking, plant height, ear height, number of leaves, leaves area, leaf area index, number of ears plant-1 , ear length, the number of rows ear-1, number of grains row-1 , number of grains of the plant, weight of 100 grains, total dry matter weight, the number of days to Physiological maturity, crop growth rate, individual plant yield and yield (tons h-1 ) were studied. The results showed that the values of the standard error (SE) in the two trial locations were low for the studied traits and within the acceptable limit except leaf area which was high in the first and second dates for the Baghdad location and for the three dates of the Diyala incident, as well as the values of the coefficient of variation (CV) were also low and within statistically acceptable limits and for all the traits studied in the three dates and for the two locations. Genetic variations were higher than the = environmental variation for most of the studied traits and the phenotypic coefficient of variation is close to the coefficient of genetic variation for the two locations and the three sowing dates, and this indicates that the traits are genetically governed. The value of heritability in a broad sense was higher than 90% at Baghdad location for first of July for the traits leaves area and its index, weight of the dry matter, number of days to physiological maturity (96.6, 97.4, 93.4 and 94.4%, respectively) and for 15 July for the traits. Leaf area and its index, and number of days to physiological maturity (94.7, 94.7 and 93.4%), and for I Aug for 9 traits; number of days silking, the leaf area and leaf area index, number of ears dry matter, days to maturity, rate of crop growth and yield the plant and unit area ((95.7, 99.4, 99.4, 94, 98.4, 95.5, 98.6, 93.4, 93.5%) Sequentially. As for Diyala, the traits of leaf area, leaf area index, number of days to physiological maturity, yield of plants, and area unit in the three dates were superior to the highest heritability (92.3, 92.3, 98.7, 73.6, 73.6%), (90.2, 90.2, 98.8, 82.9, 82 .9%), (90.9, 90.9, 86.4, 80.7, 80.7% respectively)."
"Aiming at evaluating the performance of Three-way and single hybrids and their inbreds of Maize and comparing them with the ""Iba'a5018"" variety under two plants densities, a field. The study included a comparison of 5 inbreds and 10 single inbreds and 11 Three-way hybrids as well as the control variety ""Aba'a 5018"" under two plants densities, Were (60000 and 80000 plants ha-1). Randomized Complete Block design (RCBD) with four replications under splitplots arrangement were used, the main plots were included two plants densities and the subplots were included the Genotypes (27). Results revealed that low plants density gave ear length (19.64 cm), ears number (1.158 ear plant-1), weight of 100 grains (32.11 gm) plant yield (161.32 gm). Results showed the Inbred 5 gave the high values of plant yield (126.53 gm) because it gave ear height (116.10 cm), leaves number (16.33), ears length (16.50 cm), ears number per plant (1.219 ear plant-1 ), Also the Inbred 4 gave the highest values in yield per plant (132.67 gm), highest weight of 100 grains (30.62 gm). The single hybrids (2×3), (1×3) and (4×5) gave the most significant values in plant yield (164.21, 161.84, and 157.21 gm). As they increased the plant and ears height, leaves number, and ears length it also gave the highestvalues in ears numbers. Most of the Three way hybrids superior over the single hybrids and their inbred and the control synthetic variety, the Three way hybrid (1×2)×5 has a significant differences among his parents and the control variety in yield of plant (184.23 g) ears height average (219.33 cm), ears number (1.24). The hybrids (1×4)×2, (1×3)×5 and (3×4)×2 gave a significant values compared with their parents and control variety in yield per plan. It concluded that the genetics hybrids are appropriate for the Full season, and the single hybrids superior their parents (inbreeds), The best hybrid (3×2) gave the highest yield of planted area reached (11.43 tons ha-1) The Three way hybrid (1×2)×5 gave the highest value in yield of reached (12.75 tons ha-1"
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