Some Genetic Parameters of Double Crosses under Different Planting Dates Suitable to the Middle Region of Iraq

With the aim of estimating some genetic parameters of double crosses at sowing dates appropriate to the fall season in the middle region of Iraq, a field experiment was conducted in the fields of the College of Agricultural Engineering Sciences - University of Baghdad - Al-Jadriya for the fall season 2022 using superior double crosses of maize were chosen from fifteen double crosses. It was obtained from the crossing of ten single crosses resulting from the crossing of five inbred lines (1=ZM43WIZE, 2=ZM60, 3= ZM49W3E, 4=ZM19, 5=CDCN5) by the half-dialle crossing method. Hybrids (3×5)(1×4),(3×5)(1×2),(2×4)(1×5), (4×5)(1×2), and (2×3)(1×4), compared it with the synthetic cultivar IPPA 5012 and tested it under three planting dates:1st July, 15th July and 1st August. The Randomized Complete Block Design (RCBD) was used with four replicates. The traits were studied: tassling, silking, plant height, ear height, number of leaves, leaf area, ear length, ear diameter, number of rows, number of grains per row, number of grains in a row, number of ears, average grain weight, dry matter weight, physiological maturity, ear weight, plant growth rate, individual plant yield, unit area yield, and. harvest Index. The results of the genetic analysis showed that the value of the standard error was low in all traits except for leaf area, number of plant seeds, and in the three dates, and the values of the coefficient of variation (C.V) on1st July were less than 20 in all traits except for individual plant yield, area unit yield, harvest index, and time. 15 th July and 1st August were also less than 20, and the values of genetic variance at the date of 1st July were greater than the values of environmental variance in most of the studied traits, except for ear height, ear length, ear diameter, number of rows, and ear weight. The ratio of genetic variation to environmental variation, as it was less than 1, and it had P.C.V values higher than G.C.V.The number of grains in the row, the weight of the dry matter, the physiological maturity and the plant growth rate due to the high genetic variance for it and the values of the ratio of genetic to environmental variance and then the high heritability values for it and on the date 1st August and the values of the genetic variance were greater than the values of the environmental variance in most of the studied traits.


Introduction
Genetic variations are the basis for any successful breeding program, so genetic variations in the plant population must be studied, as phenotypic variations can be measured in any environment, but they do not represent the influence of genetic variations only, but rather the influence of environmental variations, growth factors and the interaction between them and genetic variations, so the phenotype of 1259 (2023) 012101 IOP Publishing doi:10.1088/1755-1315/1259/1/012101 2 the plant is It is a shape of the genetic , environmental influence and the interaction between them.The breeding and improvement of maize plants depends mainly on the size of the genetic variations that exist between the plants, whether in obtaining new varieties through selection or in the production of hybrids by crossing between inbred lines [1].[2] indicated that selecting the plant yield alone does not give a clear genetic profile to the plant breeder because it results from genotypic -environmental interaction (GEI) , especially if we know that the plant yield is controlled by large numbers of genes associated with it and other traits.[3] obtained, when studying fifteen crosses, that the highest heritability percentage was( 86% , 85% , 85% , 82% , 77% , 73% ) for number of grain row -1 , plant height, ear height, physiological maturity, number of rows, and ear length sequentially .The results reached by [4] during their study of two single hybrids of maize for the traits of ear length, plant height and days to silking , that the heritability percentage in the broad sense of the two traits of silking and plant height was averaged 0.38 and 0.51, respectively.[5] indicated that the highest phenotypic variation was 2348.42,632.58, 181.48, and 149.45 for the number of grain plant -1 plant height, grain yield, then ear weight, and the highest genetic variation was 2245.32,472.54, 114.52, and 136.32 respectively for previously mentioned traits,.[6] indicated that the heritability percentage in the broad sense was high for the trait of tassling, amounting to 73.42% as a result of the high value of genetic variation.The results showed [7] , [24] that some traits are genetically controlled, as the value of both the standard error and the coefficient of variation decreased.And the value of GCV and PCV were close, which means that the phenotypic variance is greater than the phenotypic variance, and the highest heritability percentage was reached in the fall season for each of ear height, ear length, and number of grains, while the GCV value decreased to half the value of PCV for the two traits of the number of rows and the number of ears, and this indicates a high environmental variance.Which is reflected in the low inheritance rate.[8] indicated that the values of both genetic and environmental variance differed from zero, and heritability was high for most traits, reaching 94% for ear height, 93% for the number of days of tassling, the number of row ear -1 , 91% for each of the number of days of tassling, and plant height, and 88% for each of The number of ear rows and grain yield, 86% for the number of leaves, and 75% for the weight of 500 grains, while the lowest heritability percentage was 60% for the number of grain ear -1 .[9] noted that the heritability percentage in the broad sense is high for all traits, was 99.94%,98.84%,92.54%,91.11%and 89.72%.for the grain yield weight , 300 grains number of grain rows -1 , the number of ear rows, and then the number of ears of the plant sequentially .The study of [10] of five pure inbred lines , ten single crosses and fifteen double crosses of maize showed that the heritability percentage in the broad sense for the two traits of the m tassling and silking amounted to (26.3% and 76.7%), respectively, and 48.85%.43.9%, for two traits of plant height and ear height.[11] noted in his study of some genetic parameters in the two locations of Baghdad and Diyala under three planting dates, that the genetic variance is higher than the environmental variance for most traits, and that the phenotypic variance coefficient is close to the genetic variance coefficient, and this indicates that the studied traits are genetically controlled and that the influence of environmental factors is small.The study aimed to estimate the genetic parameters and heritability of double crosses maize under planting dates suitable for fall season in Iraq.

Materials and Methods
A field experiment was applied in the fields of the College of Agricultural Engineering Sciences -University of Baghdad in the Field Crops Department for the fall season 2022 to evaluate five superior double crosses of maize that were selected from fifteen double crosses of maize obtained from the crossing of ten single crosses resulting from the crossing of five inbred lines (1= ZM43WIZE, 2= ZM60, 3= ZM49W3E, 4= ZM19, 5= CDCN5).By the half-diallel crossing method, which is hybrid 1 = (3×5)(1×4), hybrid 2 = (3×5)(1×2),hybrid 3=(2×4)(1×5) ,hybrid 4=(4×5)(1×2), hybrid 5=(2×3)( 1×4) and compared with synthetic cultivar IPPA 5012 and tested under three planting dates.It is 1 st July, 15 th July, and 1 August.The land was prepared for cultivation and the site of the experiment, through perpendicular plowing, harrowing, and leveling according to the recommendations.The land was divided into plots (3×3) m 2 , the distance between rows was 75 cm, and between one plant and another, 25 cm.Fertilization was done with triple superphosphate fertilizer (46% P 2 O 5 ) at a rate of 200 kg P 2 O 5 ha -1 in one batch before planting, and nitrogen fertilizer 350 kg N ha -1 in the form of urea (46% N) in three batches, the first two weeks after germination, the second when the plant height is 30 cm, and the third after flowering The process of weeding was carried out manually several times during the season and according to the need, as well as field irrigation operations were carried out as needed.Seeds were sown at a rate of 2-3 seeds in each hole, and the number of plants was thinned to one plant.The experimental land was divided into four replicates according to the randomized complete block design (RCBD) in the split plots arrangement.The main plots included the three planting dates and the secondary plots were double crosses with the comparison cultivar.Five intermediate plants were taken for each experimental unit, which were chosen randomly, with the exclusion of terminal plants, and the following traits were measured: Number of days from sowing to 50% tassling and silking, plant height, ear height, leaves number ,leaf area ,ear length ,ear diameter, rows number, grain number row -1 , number of grain ear -1 , number of ears, grain weight, number of days to physiological maturity, plant growth rate, dry weight, harvest index, plant yield, and unit area yield.The analysis was done Statistical analysis for each of the traits according to the analysis of variance ANOVA with RCBD design.Significance was tested with the F test at the level of significance of 0.05, and the arithmetic means were compared using LSD (the least significant difference) at the level of significance of 0.05 for all means according to [12] using the Genestat 2014 program.For each planting date separately, genetic analysis and genetic parameters were estimated Such as genotypic , phenotypic and environmental variance, heritability in the broad sense, h 2 b.s%, coefficient of genetic variance(GCV%) coefficient of phenotypic variance .It was calculated as in the following equations Since: MSV: mean squares for genotypes MSe: mean squares experimental error r: the number of replicates σ 2 g, σ 2 E and σ 2 P = genotypic, environmental and phenotypic variations, respectively.The genetic variation coefficient (GCV) and the phenotypic variation coefficient (PCV) were estimated as follows: The percentage of heritability in the broad sense, h 2 b.s, was also calculated according to the following equation: As they are genetic and phenotypic deviation respectively .The heritability values within the limits suggested by [13] are less than 20% low, 20-50% medium and more than 50% high.

Genetic Parameters
Genetic variations are among the basic factors for plant breeders, as they represent the basis on which selection is based.Based on this, the estimation of phenotypic, genetic and environmental variations, coefficients of phenotypic and genetic variation, and the degree of heritability in the broad sense provide important information that can be inferred from them on the most appropriate methods to improve crops.Genetic analyzes were conducted to estimate these parameters for each planting date separately, and it is clear from the table of analysis of variance in table (1,2 and 3) that there are highly significant differences.

Genetic Parameters at the First Date1 st July
The results of Table (4) show that all the standard error values of the measured traits are low except for the leaf area trait whose value was high.The decrease in the standard error values indicates the similarity of the trait data and its proximity to the arithmetic mean.The values of the coefficient of variation (C.V) for the studied traits were less than 20%, and they indicated the homogeneity of the data, except for the plant yield, the area unit yield, and the harvest index.The values of genetic variance were greater than the values of environmental variance in most of the studied traits, which indicates that the variance between genotypes was mainly due to genetics with little effect of the environment and then be inherited, but some traits such as ear height, ear length, ear diameter, number of rows and grain weight The values of genetic variance were lower than the environmental variances, by (53.78%, 16.19%, 40.87%, 60.35%, and 13.10%), respectively.Which indicates that the contribution of the environment was greater in phenotypic variation in those traits.These traits also showed a decrease in the ratio of genetic variance to environmental variance, as it was less than 1.In such traits, selection is more difficult than the previous traits and takes a longer period due to the difficulty of distinguishing the phenotype of the plant, is it genetic or environmental influence, and it had higher P.C.V values than the G.C.V.And unlike the traits in which the genetic variance is high, the P.C.V values approached the G.C.V values, and the genetic-to-environmental variance ratio increased, which led to a higher heritability ratio.These results are normal because the phenotypic traits are the result of the genetic and environmental influence and the interaction between them.This is consistent with the results of [14], [15], [16], [17], [18]and [19]The amount of the heritability percentage refers to the degree of confidence with which the genotype can be distinguished through its phenotypic expression.Table (4) shows that a large percentage of the phenotypic variation was explained through the genetic component in most traits.Based on the classification proposed by [13], the degree of heritability was high in the traits grain weight, dry matter weight, and plant growth rate, reaching (0.736089, 0.838034, and 0.831341)%, respectively, while the characteristic of ear height, ear diameter, and number of rows gave low values of heritability amounting to ( 0.316078, 0.371581, and 0.283893 (%), while the onther traits gave high to medium values that ranged Between (0.455937 _ 0.689498)%, the high heritability percentage of these traits may be the result of the effects of the gene action, and these traits may respond to direct selection.

Genetic Parameters on the Second Date,15 th July
The results of Table (5) show that all the standard error values of the measured traits are low, except for the two traits of leaf area and the number of grains per plant.Their values are high.The decrease in the standard error values indicates the similarity of the trait data and its closeness to the arithmetic mean.The C.V values for the traits were less than 20%, which is It indicates the acceptance of the homogeneity of the data, except for the harvest index , which was higher than 20%.The genetic and environmental variance values differed on the 15 th of July date from the 1 st of July, where the genetic variance for ear height, ear length, ear diameter, number of rows, and ear weight was (60.3816, 1.0959, 41.4346, 0.3577, and 754.3048), respectively.It is higher than the environmental variance, and thus it behaved differently from its behavior at the planting date, 1 st July, which indicates that the variance between the genotypes was mainly due to genetics with an environmental effect, but the genetic variance decreased in some traits such as plant height, number of leaves, and leaf area.The number grains ear -1 , the number of ears s, and the harvest index indicate environmental variation compared to what it was on the 1 st of July date.Any factor that reduces the environmental differences will increase the heritability percentage [13], [20], [21].Accordingly, the percentage of genetic variation to environmental variation varied, and it was less than 1 for the traits: plant height, number of leaves, leaf area, number of grains per plant, number of ears, and harvest index indicating a decrease in genetic variation.Environmental conditions have an effect on the trait, which affects the selection for the trait and delays the period of its improvement The P.C.V values were higher than the G.C.V values at this time, and this indicates that the differences was not a result of genotypes only, but rather due to environmental influences, and this is consistent with the results of [9], [22], [23].Grains number row -1 , dry matter weight, physiological maturity, plant growth rate due to the high genetic variance for it, the values of the ratio of genetic to environmental variance, and then the high heritability values.Table (5) showed that the values of the heritability percentage decreased for some traits compared to what it was on the date of1 st July, as in the traits of the number of leaves, leaf area, number of grains per plant, and harvest index.Plant and the largest increase was the crop growth rate, as it increased from 0.464950 to 0.923253.The change of inheritance values according to different dates is due to the environmental genetic interaction and its effect on the gene action and the extent to which it is affected by environmental conditions, and it may be due to the presence of some silent genes that start their activity under some biotic or abiotic stress , or it may be due to changes in what is known as Epigentic heredity.

Genetic Parameters in 1 st August
The results of Table (6) differed from the results of the first date July 1 and the second date July 15, whether by increase or decrease.The results indicate that all the standard error values for the measured traits were low except for leaf area and the number of grains per plant whose value was high.The C.V values for the traits were less than 20%, which indicates acceptance of the homogeneity of the data.The values of genetic variance were greater than the values of environmental variance in most of the studied traits, but some traits such as number of leaves, ear length, number of rows, number of grains per ear, average grain weight, ear weight, individual plant yield, area unit yield, and harvest index It was lower than the canvas.The values of genetic variation were lower than the environmental variation, and thus they behaved differently from the behavior of the other two dates.The ratio of genetic variance to environmental variance differed and was less than 1 for the traits: the number of leaves, ear length, number of rows, number of plant grains, grain weight, ear weight, individual plant yield, area unit yield, and harvest index indicating a decrease in genetic variation in these traits, and that the environment has an influence on them, which affects selection and delays the period of improvement.The P.C.V values were higher than the G.C.V values in all studied traits, and this indicates that the differences are due to the influence of the environment as well.

Conclusion
The double crosses differed in significant genetic differences in the three planting dates for the studied traits.Total dry weight and crop growth rate, were characterized by the highest broad sense heritability in the first and second date.In the third date was decreased slightly.The ear diameter trait excelled with the highest heritability percentage in the third date, which indicates the importance of adopting it as selection criteria for mentioned planting dates.

Table 1 .
Mean squares for double crosses of maize at planting date 1 st July.

Table 2 .
Mean squares for double crosses of maize at planting date 15 th July. con

Table 3 .
Mean squares for double crosses of maize at planting date 1 st August.

Table 4 .
Some genetic parameters of the studied traits of double crosses of maize under planting date1 st July.

Table 5 .
Some genetic parameters of the studied traits of double crosses of maize under planting date15 th July.

Table 6 .
The values of P.C.V were close to G.C.V in days number to tassling and silking , ear diameter, dry matter weight and physiological maturity due to the high genetic variance and the values of the ratio of genetic to environmental variance and then the high heritability values.The table showed a decrease in the percentage of heritability in the number of rows, number of grains per plant, grain weight, individual plant yield, unit area yield, and harvest index compared to what it was on1 st July and 15 th July .Some genetic parameters of the studied traits of double crosses of maize under planting date1 st August.