For more than tens of years, people have tried to find varieties, this effort continued for a long period of human history and its struggle with nature, it was possible to introduce many new items, high level of performance and productivity, keeping pace with the steady increase in the world's population, with the support of traditional breeding methods and methods of modification (genetic modification), apoptosis, tissue culture and others, at 1950, the first synthetic hybrid was produced at the University of Iowa from 16 strains, it was the cultivar SSS relative to the Stiff Stalk Synthetic [1], in developing countries, the development and cultivation of synthetic varieties is considered, better than the hybrid, because the hybrid needs accurate methods in its evaluation, cultivation and production on a commercial scale. In addition, the productivity of synthetic varieties in unstable environmental conditions is better than the production of hybrids, with the possibility of cultivating it from 4-5 years in the absence of genetic mixing [2].

The synthetic variety is defined as the group of plants produced with all possible combinations of a series of crosses (breeds, hybrids or clones), which results in a number of crosses that differ among themselves, depending on the number and type of fathers involved in their taxation and the method of taxation, the number of the resulting synthetic varieties increases with the increase in the number of parents [2]. Whereas Variety has been defined in general, it was a group of similar cultivated plants, characterized by certain morphological, physiological or genetic characteristics, if they reproduce sexually or vegetatively, they retain those characteristics that distinguish them from other varieties of the same species, it has the criteria of Uniform, Destincteness, Stability and Variety value, in addition to its agricultural efficiency, it has the ability to reproduce for several generations (4-5) years or more, without losing its distinctive qualities and synthetic varieties are Synthetic Varieties, the resulting pure strains are more stable than others [3].

Steps to Configure Synthetic Variety

The synthetic variety consists of a group of pure strains, a group of vegetative strains or a group of genotypes that were previously selected on the basis of their ability to compatibility. It was formed by:

• The strains that were derived from an open-pollinated variety cross with a test variety with a broad genetic base (apical cross) and select (10%) of the superior strains on the basis of their general ability to combine

• Superior strains are vaccinated with each other with all possible possibilities. If, for example, (8) strains, the resulting hybrids with all possibilities are (28) hybrids

• Mix equal quantities of camel seeds and plant them in isolated plates

• Seeds of individual hybrids are harvested without selection to form the synthetic variety

In order to perpetuate the synthetic variety, a hundred pods are harvested annually in the case of maize, for example and from its superior plants to preserve the variety from deterioration.

Features of Synthetic Variety

• The cost of producing its seeds is low as it can be used for several generations

• Synthetic varieties can be used in marginal environments because it has a wide genetic base

• The plant breeder can return the synthetic variety at any time, as the plant breeder keeps the strains included in the synthetic variety in isolation

• It can be used in crops that are difficult to produce hybrids because pollination is not controlled, for example, fodder crops whose floral composition is not suitable for camel production

• The synthetic variety can be preserved for a long time using aggregate selection to prevent deterioration and if it deteriorates, it is possible to refer to the original strains that were kept in the research station periodically

Estimate the Product of Synthetic Variety

The synthetic varieties are an extension of the marital hybrid. Wright used an equation to estimate the expected performance of the synthetic variety, as follows:

Whereas :

F2   =    The expected product of the synthetic variety

F1   =    The average yield of the first generations of hybrids from all the crosses included in it

P      =    The average product of the pure strains included in the synthetic variety

N     =    The number of strains included in the cultivar

Therefore, if the rate of the first generation of hybrids is increased, it leads to:

• Increasing the synthetic variety

• Increasing the number of fathers, which increases the performance of synthetic varietie.

• Increasing the performance of pure strains, which increases the performance of synthetic varieties

This equation indicates the possibility of improving the yield of the second generation of the synthetic variety, by improving the ability to match the first generation, increasing the number of parents (n) and improving the performance of parents. In general, it is difficult to maintain the increase in the performance of fathers and the first generation when the number of fathers increases, so it is determined precisely [4].

Criteria for Deriving Synthetic Varieties

Breeding of new varieties depends on finding a new high combination of alleles, it was subsequently supplemented by testing and selecting the desired forms through self-pollination of individuals, as between Raeed and Saifuldeen [5] and Saifuldeen and Raeed [6] the variables that have the ability to be inherited can be found mainly, by controlling crosses between the tested strains of higher production or a comparison of different environmental conditions among breeding lines, in addition, the breeding of the synthetic variety depends on the elite of the genetic material and some traits, that were introduced from the strains introduced into the cross-breeding program [1]. The high productivity of synthetic varieties depends on a relatively constant rate, for several years and in several locations on the rate of productivity and the number of genotypes included in its genetic structure, which increases the capacity of its genetic base and helps it adapt to different environmental conditions or growth factors [7].

Crossing is one of the methods used to derive new varieties, especially in third world countries, poor countries or countries that suffer from drought or through genetic mutations, whether they are spontaneous or developed [8]. Since these mutations are few and the results are not guaranteed, many varieties have been developed through multiple cross-breeds between different breeds, have desirable characteristics, to these efforts are added soil and crop service operations, as a tool to determine the performance or behavior of those derived varieties under the influence of the input factors, it may reduce the food security obsession, which hangs over many interested circles in this regard [9]. It was shown by Edwards and Lamkey [10] that the number of synthetic taxa, which can be obtained by having multiple fathers, depends on the application of multiplications with all possible combinations between the parents. Smith [11] indicated that genetic variation between breeds is the key to growth, performance and the ability to produce high hybrids and newly derived varieties. Haberer et al. [12] mentioned that the inherited mutations caused by the exposure of the chromosomal set to various stresses, such as passive hybridization, doubling, extreme selection or change in growth factors, it may cause the emergence of new phenotypes due to a change in the sequence of DNA nitrogenous bases, will show changes in gene expression. Hamdallah [13] emphasized that individuals and parents possess a large degree of genetic variance, it can contribute significantly to hybridization and the strength of the hybrid qualifies it for growth, under the influence of factors that neither her parents nor her ancestors can excel in.

In a study by Ibrahim [14] that most economic traits are under the influence of the precise action of genes but it is a cumulative act involving a large number of genes, as well as the possibility of locating most of the sites, which controls quantitative traits, for more than 130 quantitative traits for nine types of crops using the QTL (Quantitative Traits Loci) marker genes. Al-Sahoki and Al-Falahi [15] indicated that the development of most synthetic varieties or their parents, DHS (Duplication Haploid Single), because it is similar to the high appearance, ease and speed of production but it leads to fewer genetic variations when selecting among its plant communities in the future, which was necessary to improve desirable qualities. Brummer [16] explained that genetic screening of a population that includes varieties and hybrids, indeed, it proves that the varieties are more heterogeneous in terms of phenotype and less genetically, hybrids have a higher frequency and genetic heterogeneity and a greater number of different alleles in identical genetic sites compared to the synthetic varieties.

Synthetic Variety and Genetic Action

A gene action is defined as the behavior or manner in which genes express themselves in a genetic population, genetic action is measured as the components of genetic variance. Genetic action is useful in selecting parents to be used in crossbreeding programmes, in choosing the appropriate breeding method for genetic improvement of various quantitative traits, there are two types of genetic action.

Additive Gene Action

The additive genetic variance and the superiority variance of the type (extra x additive) include.

Non-Additive Gene Action

Sovereign variance and superiority variance include the two types (extra x sovereign) and (sovereign x sovereign).

The total variance seen is known as phenotypic variance, the differences in phenotypic form are due to the influence of both genetic structure and environmental factors on each member of the clan. The environmental variance of a trait is not always constant. Rather, it changes with the change in the genetic structure, so it is greater in pure breeds than in ordinary varieties. Genetic variance reflects the extent to which genotype contributes to the overall variance of a trait, several methods and systems have been adopted to estimate the genetic action and components of phenotypic variance [17].

Future research can depend on the use of PCA (Principle Component Analysis), to analyze the stability of varieties when changing growth factors in the form of GGE (Genetic x Genetic Environment Interaction), which represents the interrelationships between cultivars and their environments and growth factors that influence them resulting from gene expression images to determine the relationship between genes [18]. Bhatnagar et al. [19] indicated that both genetic variance and isolation, that results from cross-pollination of cultivars and can reduce the effects of (damaging) deletion mutations, which can be disposed of by retrocrossing. While Baktash and Al-Aswadi [20] mentioned that the sources of variation that affect the external appearance and genetic makeup, were the genetic structures and environmental differences within the treatment and the impact of unrelated environmental differences (external factors). The genetic and environmental interference works to reduce the association between genetic and phenotypic values ​​resulting from the multiple influence of the gene, which affects two or more traits and its isolation causes a genetic variation in the traits it affects. Arncken and Dierauer [21] indicated that the difference in compositional varietyes in yield, it was due to the difference in the genetic effects of genes in the distribution of dry matter produced between the important parts of plants, which leads to giving a kind of high or low adaptation to the variety under the influence of certain factors and thus raising or reducing the resulting yield.

Brewbarker [22] indicated that crosses may prevent the influence of harmful recessive genes in first generation crosses, it comes from one of the parents with the dominant alleles of the other, as the genotype of the positive dominant alleles AA gives two doses (two units) of the protein, instead of a single dose (one unit) in case of genetic variation Aa, therefore, internal education may be appropriate for this type of genetic action, which may contribute to the inheritance of quantitative traits and to show a high percentage of hybrid vigor even in the second generation by covering harmful genes. Brummer [16] obtained that the relative superiority of synthetic varieties over their parents, it may be due to the influence of dominance and partial dominance as a result of having part of the hybrid power, as for the higher yield of pure strains, the host genes are responsible for its manifestation as a result of the selection act.

Synthetic Variety and Polycross

The use of multiple crosses in cross-pollinated plants is common or those that have the ability to pollinate by wind and insects at a high rate, in all cases when tested, it is preferable to use the design and analysis of experiments according to the Latin square system when the number of genetic groups (breeds, plant communities or varieties) is less than ten. At the case of more than that, the use of a full-segment design is appropriate for it. At the event that the plant communities are not equal or the quantity of seeds of the parental genotypes is not equal, it is preferable to apply adjacent plots or plates or the seeds can be mixed in equal quantities for all the parental genotypes (breeds or hybrids), it's called the random cross-crossing (reverse) of the parents, the members of the resulting offspring are called polycross of progeny. At all cases, it is expected that all genetic combinations will occur in a non-random manner between parents and randomly between members of the offspring. The additional effect of genes appears higher than the non-additive effects in the resulting offspring, which represent the nucleus of the synthetic variety [23].

The random mating program is an important way to ensure the random mating of all breeds, its importance appears when testing the performance of cultivars or when improving synthetic cultivars or improving old cultivars. Some of its genetic parameters can be estimated [24]. The multiple cross-breeding system is one of the common methods of ensuring random cross-fertilization to assess the performance of the genotypes involved in cross-breeding (parents and their offspring), when a number of parents (breeds) are taken and multiplied among themselves for all the possibilities of mixing pollen to produce members of the first generation (F1), then mix the resulting seeds F1 in equal quantities for the group of plants descended from the same number of strains, to produce a new genetic combination to produce the new variety, it can be said that the parents were multiplied by a random multiplication or entered into the group of multiple multiplications [25].

Brummer [16] defines multiple multiplication as the set of multiplication, which takes place between a number of genetic structures (breeds, clones, hybrids or others) among members of the community at random or it was a number of crosses that take place between 4-16 genotypes or more in a directed or random manner. Snyder [26] defined it as the method of cross-breeding a group of genotypes by mixing their pollen grains or mixing the seeds of the selected parents with a high ability to combine. Tysdal and Crandall [27] citing Dragan [28], the first to use this method and proposed to call it polycross to distinguish it from Multicross, several explanations have been given about the importance of this method, including what was presented by Brummer [16] about the participation of the effect of several pairs of genes in the manifestation of the trait, that is, the effect of the simple gene was the main reason for the manifestation of the trait.

Brummer [16] mentioned that the sources of genetic differences for inferred synthetic varieties, be the result of three cases:

• Inter-specific differences representing the purity of the same strain and resulting from the number of times the self-pollination was carried out

• Difference between breeds depends on the ability of the breed to transfer its genetic traits when used as a mother or father breed

• It depended on the amount of pollen that they contributed, which could not be controlled or counted even if the number of seeds mixed or the number of plants used for cross-breeding was equal

Pointed out that most of the genetic effects resulting from members of the synthetic type may have additional and sovereign effects or effects of different sovereignty.

Performance of Synthetic Varieties and the Number of Strains

The behavior of synthetic varietyes depends mainly on the number of parents and their general ability in the synthetic variety, which was due to the agricultural value of the parents and their hybrids, the fertility of the parents and the degree of cross-pollination with them [29]. It was very necessary when deriving synthetic varieties and determining the optimal number of strains, which was included in its deduction in order to improve its genetic base and increase its productive capacity in a way that ensures benefiting from the strength of the hybrid in its ability to combine [30]. Knowing the genetic behavior of synthetic varieties and their parents (pure strains) is of great importance in breeding and improvement programs in maize. The genetic behavior depends on the effect of genetic action, the percentage of heritability and the ability to combine between strains, therefore, the development of strains with a general federal ability, GCA and especially SCA, is the first basic steps to ensure high-productivity hybrids and cultivars, it was known that the yellow corn plant is monoalteric, it facilitates the easy application of the multiple pollination system between its strains [1]. Hallauer and Sears [31] stated that parental behavior is the result of an additive gene action, it was important to maintain the behavior of synthetic species, which allows the regulation and exploitation of the hybrid vigor by the hybrids resulting from cross-breeding between pure breeds. Baktash [32] shows that the program for the production of synthetic varieties, depends on the strains introduced from other countries as well as the pure strains derived from the appropriate genotypes for the program area (locally produced), in both cases, it must be evaluated in two stages: The first is by apical cross, then cross-hybridization between breeds superior in their characteristics, especially when the numbers of breeds are large but in the case of a small number of breeds, it is preferable to conduct a Dillel cross between them directly, the individual crosses that are subsequently compared are elicited, the general and specific capabilities of the union are estimated to produce single, triple or even crosses and then cultivars consisting of four, five or more breeds.

Edwards and Lamkey [10] indicated that grain yield was lower in cultivars with fewer fathers, compared to the varieties with the most number of fathers, whose phenotypic and productive characteristics were more stable when grown in environments or under the influence of different growth factors, they explain this by the fact that the first contains a higher hybrid strength than the second. Lambert [33] noted that the rate of genetic isolations in a variety of maize cultivars, depends on the number and extent of differences between the genetic structures (parents or hybrids) included in their composition. In a study to evaluate the performance of synthetic varieties of yellow corn containing different numbers of strains 5, 6, 8 and 10 pure strains with common parents. Smith [11] mentioned that the cultivars with the higher number showed superiority over the other cultivars with the lower number in terms of grain yield and its components. Stojakovic et al. [1] found that pure strains selected from one cultivar are usually strongly genetically related to each other, therefore, the percentage of hybrid vigor resulting from a hybrid and varieties of these strains was not always high.

Walsh [34] obtained that accurate estimates of the number of breeds (parents) involved in the production of synthetic varieties, it was one of the effective means to determine the causes of future deterioration due to genetic isolations that occur later. Al-Sahoki [35] mentioned that the final yield of the plant (whatever the nature of its genetic combination), it occurs as a result of genetic and environmental interference, whether by an interactive model GE or an additive model G+E, the same researcher indicated that the high growth rate and the number of seeds, they were the two most important factors that affect the increase in the yield of the improved variety or the hybrid. Brummer [16] found that the number of strains has a positive effect for some traits due to the presence of a percentage of hybrid vigor, which were positive or negative or with large or small values, which proves the existence of a link between the strains and the synthetic varieties derived from them, because genetic action differs in its effect on growth characteristics, dominance may be complete or partial or superior in hybrids despite the appearance of the extra gene action in the derived cultivars.

Evaluation of Synthetic Variety Compared to Their Parents

Breeding of new synthetic varieties depends on finding a new high combination of alleles, it was subsequently supplemented by testing and selecting the desired forms through self-pollination of individuals, since the variables that have inheritance can be found mainly, by controlling crosses between tested strains for higher yield or a comparison of the different environmental conditions among the breeding lines. The high productivity of synthetic varieties at a relatively constant rate for several years and in several locations depends on the rate of productivity and the number of genotypes included in its genetic structure, which increases the capacity of its genetic base and helps it adapt to different environmental conditions or growth factors. The breeding of the synthetic variety depends on the elite of the genetic material, as well as some of the traits that were introduced from the breeds entered in the cross-breeding program [7].

The genetic behavior depends on the effect of genetic action, the percentage of heritability and the ability to combine between strains, by knowing the genetic behavior of synthetic varieties and their parents (pure breeds), which were of great importance in genetic education and improvement programmes, accordingly, the development of strains with general federal ability GCA and especially SCA, it was one of the first essential steps to ensure high yielding hybrids and cultivars [1].

One of the methods used to derive new varieties, usually through crossing, especially in third world countries or poor countries or those suffering from dehydration or through genetic mutations, whether spontaneous or induced, since these mutations are few and the results are not guaranteed, many varieties have been developed through multiple cross-breeds between different breeds, which bear desirable traits [11]. In addition to these efforts, soil and crop service operations are added as a tool to determine the performance or behavior of these derived varieties, under the influence of the input factors, it may reduce the concern for food security, which hangs over many circles interested in this regard [9].

Smith [11] found that in the case of a small number of breeds, it is preferable to conduct a cross cross between them directly, the individual crosses that are subsequently compared are elicited, estimate the general and specific capabilities of the union to produce single, triple or even crosses, then varieties consisting of four, five or more breeds. Stojakovi et al. [1] pointed out the importance of genetic divergence between breeds when developing synthetic varieties, at the same time, they showed that similar genetic structures, they may possess similar heterogeneity in genotype and phenotypic behavior that reduces their ability to compete in a certain range of growth factors. Shapiro and Wortman [36] showed that the difference in the structural classes in the yield, it was due to the difference in the genetic effects of genes in the distribution of dry matter produced between the important parts of plants, which leads to giving a kind of high or low adaptation to the variety under the influence of certain factors and thus raising or reducing the resulting yield.

Al-Sahoki [35] mentioned that the final yield of the plant (whatever the nature of its genetic combination), it occurs as a result of genetic and environmental interference, whether by an interactive model GE or an additive model G+E, indicated that the high growth rate and the number of seeds, they were the two most important factors that affect the increase in the yield of the improved variety or the hybrid. Al-Sahoki and Al-Falahi [15] indicated that the development of most synthetic varieties or their parents at the present time, DHS (Duplication Haploid Single), it gives a high appearance, as well as the ease and speed of production but it leads to a lack of genetic variations when selecting in its plant communities in the future, which was necessary to improve the desired qualities.

Al-Ghamdi [29] confirmed from the results of his study that the synthetic variety achieved an upper limit in all the traits under study, they are (number of days until flowering, plant height (cm), number of branches, number of pods/plant, number of pods/main branch, number of seeds/plant, seed yield/plant, weight of 100 seeds), compared to the breeds included in it (Hasawi 2, Jazira 2, Gazira 716 and Sakha 1), pointed out that the synthetic varieties are the most tolerant of drought and the most stable and adaptable to climatic changes. While Al-Jubouri [37] mentioned that the synthetic type had a value greater than the correct one, compared with the parents involved in it and for all the studied traits, except for the characteristic of average seed weight, it was close to the correct one.

From all previous studies, the correct scientific basis for breeding synthetic varieties remains, it was the testing of parents or plant communities containing preferred alleles that carry the desired traits, not high yielding hybrids or desirable phenotypic traits, by developing pure strains with high general and private federation susceptibility, which was the first basic steps to ensure hybrids or synthetic varieties of high productivity.

1. Stojakovic, M.G. et al. “B73 and related inbred lines in maize breeding.” Genetika, vol. 37, no. 3, 2005, pp. 245-252.

2. Fehr, W.R. Principles of cultivar development. Vol. 1, MacMillan, New York, 1987, pp. 66-70.

3. Zsubori, Z. et al. “Inheritance of plant and ear height in maize (Zea mays L.).” Agricultural Research Institute of the Hungarian  Academy  of  Sciences,  Martonvásár,  2002, pp. 1-4.

4. Al-Jubouri, J.M.A. Advanced plant breeding lectures. College of Agriculture, Tikrit University, 2020.

5. Raeed, M.A. and S.A. Hasan. “Estimation of components of genetic variance using Jinks-Hayman method analysis on the crop of faba bean (Vicia faba L.).” International Journal of Agricultural Statistical Science, vol. 16, no. 1, 2020, pp. 1897-1903.

6. Saifuldeen, A.H. and R.M. Abdullah. “Estimating the performance and gene action of a number of individual genotypes and hybrids on the crop of faba bean (Vicia faba L.).” Plant Archives, vol. 20, no. 2, 2020, pp. 8981-8988.

7. Smith, M. “Anthracnose stalk rot resistance from exotic maize germplasm.” Annual Report, United States Germplasm Enhancement of Maize Project, 2008, pp. 1-6.

8. Saifuldeen, A.H. and R.M. Abdullah. “Characterization of genetic variability through the use of RAPDs markers of a group of native and commercial genotypes of bean species.” International Journal of Agricultural Statistical Science, vol. 17, no. 1, 2021, pp. 1703-1817.

9. License, S.A. “Maize.” New World Encyclopedia, 2008. http://www.newworldencyclopedia.org/entry/Maize.

10. Edwards, W.J. and K.R. Lamkey. “Quantitative genetics of inbreeding in a synthetic maize population.” Crop Science, vol. 42, 2002, pp. 1094-1104.

11. Smith, E.S. “Breeding synthetic cultivars.” Encyclopedia of Plant and Crop Science, University of Arizona, Tucson, USA, 2004, pp. 1-2.

12. Haberer, G. et al. “Structure and architecture of the maize genome.” Plant Physiology, vol. 139, no. 1, 2005, pp. 1612-1624.

13. Hamdallah, M.S. Relative number of genes and some parameters of hybrid vigor in maize. PhD thesis, Field Crops Division, Faculty of Agriculture, Baghdad University, Iraq, 2006.

14. Ibrahim, M.A. Plants and seeds of hybrid corn variety CH 877148 - US Patent 7193146. 2007, pp. 1-42.

15. Al-Sahoki, M.M. and A.O. Al-Falahi. “Genome duplication and its relationship to plant breeding and adaptation.” Iraqi Journal of Agricultural Sciences, vol. 39, no. 6, 2008, pp. 49-71.

16. Brummer, E.C. Advanced plant breeding. CRSS/HORT 8140, 2008.

17. Hassan, A.A. Improving quantitative traits: Biological statistics and its applications in the plant breeding program. Arab House for Publishing and Distribution, Cairo, 2005.

18. Kim, K. et al. “An efficient measure of similarity between gene expression profiles through data transformations.” University of California, Berkeley, 2006, pp. 1-22.

19. Bhatnagar, S. et al. “Combining abilities of quality protein maize inbred.” Crop Science, vol. 44, 2004, pp. 1997-2005.

20. Baktash, F.Y. and M.H.Y. Al-Aswadi. “Phenotypic and genetic correlations of some traits in maize.” Iraqi Agriculture Journal, vol. 36, no. 3, 2005, pp. 57-62.

21. Arncken, C. and H. Dierauer. “Hybrid varieties for organic cereals? Prospects and acceptance of hybrid breeding for organic production.” Research Institute of Organic Agriculture (FIBL), CH-5070 Frick, Switzerland, 2006, pp. 1-7.

22. Brewbarker, L.J. “Registration of nine maize populations resistant to tropical diseases.” Crop Science, vol. 3, 2009, pp. 10-13.

23. Mark, E.W. et al. “Quantitative relationships between pollen-shed density and grain yield in maize.” Crop Science, vol. 43, no. 3, 2003, pp. 934-942.

24. Grander, C.O. and S.A. Eberhart. “Analysis and interpretation of the variety cross diallel and related population.” Biometrics, vol. 22, 1966, pp. 439-452.

25. Allard, R.W. Principles of plant breeding. John Wiley and Sons, Inc., New York, 1960.

26. Snyder, E.B. A glossary of tree improvement terms. Southern Forest Experiment Station, Forest Service, U.S. Department of Agriculture, 1972, pp. 1-6.

27. Tysdal, H.M. and B.H. Crandall. “The polycross progeny performance as an index of the combining ability of alfalfa clones.” Journal of the American Society of Agronomy, vol. 40, 1948, pp. 293-308.

28. Dragan, M. “Identification of inbred lines as a source of new alleles for improvement of elite maize single crosses.” Crop Science, vol. 29, 1989, pp. 1120-1125.

29. Al-Ghamdi, S.S.H. Application of biotechnology in improving field crops (beans). PhD thesis, College of Food and Agriculture Sciences, King Saud University, Kingdom of Saudi Arabia, 2009.

30. Duc, G. “Diversity maintenance and use of Vicia faba L. genetic resources.” Field Crops Research, 2008, doi:10. 1016/j.fcr.10.003.

31. Hallauer, A.R. and J.H. Sears. “Second phase in the evaluation of synthetic varieties of maize for yield.” Crop Science, vol. 8, 1968, pp. 448-451.

32. Baktash, F.Y. “An experimental program for the generation of single cross maize.” Iraqi Journal of Agricultural Sciences, vol. 26, no. 2, 1995, pp. 131-139.

33. Lambert, J.R. “Dedication: Denton E. Alexander, teacher, maize geneticist, and breeder.” Plant Breeding Reviews, vol. 22, edited by Jule Janick, 2003.

34. Walsh, B. Inbreeding and crossbreeding notes from a short course  taught. University  of  Aarhus,  Lecture  6,  2006, pp. 1-17.

35. Al-Sahoki, M.M. “A new horizon for predicting the number of marital crosses from cross-breeds with multiple possibilities.” Iraqi Journal of Agricultural Sciences, vol. 38, no. 1, 2007, pp. 125-127.

36. Shapiro, C.A., and C.S. Wortman. “Corn response to nitrogen rate, row spacing and plant density in Eastern Nebraska.” Agronomy Journal, vol. 98, 2006, pp. 529-535.

37. Al-Jubouri, R.M.A.H. Genetic analysis and evaluation of some promising genotypes and the synthetic cultivar derived from them for salinity tolerance in peas (Vicia faba L.). PhD thesis, College of Agriculture, Tikrit University, 2016.