Performance of some Three-Way Cross Hybrids and Their Parents of Maize in the Middle Region of Iraq

There is increasingly demand of maize as a staple food in poultry industry in Iraq, where the average production of yield 4.5 tons, which is still faint as compared to neighbor countries. 30 of Three-Way Cross Hybrids of Maize along with five parental inbred lines were evaluated in four replications during the 2017 fall season at the research station of Agriculture College/Al-Jadrya, Baghdad to evaluate their performances and estimate the heterosis for grain yield (GY), and related traits. Most of the studied three-way cross hybrids out-yielded their parental inbred lines for the studied traits. TW8 and TW10 were identified as the excellent hybrids with average yield 219 and 214 gm/plant respectively with positive heterosis reached 72 and 62% respectively.


Introduction
Maize (Zea mays L.) is an annual crop, which is grown over a wide range of agro-climatic of Iraqi environments.Maize is a multipurpose crop, but it use mainly as fodder for animals feeding purposes.Grains of maize are essential component in poultry feeding, while its vegetative parts are using for poultry and livestock feeding [1,2].The growing poultry industry in Iraq resulted in increased the demand of grains maize.In Iraq during 2021 season, maize was cultivated over area of 78000 thousand hectare with average production of yield 4.79 tons [3].This productivity rate is faint as compared to neighbor countries.The dependence of hybrids was driven by the yield advantage over local cultivars.According to Miranda [4], heterosis is the genetic potential expression of the superiority of a cross in relation to its parents.The biological bases of heterosis are described by the trait-specific performance of highly heterozygous F1 hybrids compared the mid-or best parent [5].Yet, heterosis in maize has been wildly investigated for different sets of developed inbred lines [6].Among hybrids, three-way cross hybrids are orderly used because they are cheap in seed production.Three way crosses are intermediate between single and double cross hybrids with respect to uniformity, yield, stability and the relative simplicity of selecting and testing [7].The objective of this study was to evaluate their performances and estimate the amount of heterosis with respect to grain yield and yield related traits among 30 Three-way cross hybrids, in addition to characterize the superior hybrid for future maize breeding schemes in Iraq.

Materials and Methods
The breeding material included 30 three-way cross hybrids of maize with five of best their parents (inbred lines), where grown in a comparison trail.These genotypes materials were derived during 2017 spring season.The experiment has been carried out at the research station of Agriculture College/Al-Jadrya Baghdad University during fall season, 2017, in randomized complete block design with four replications.Each plot consisted of five 4-m long rows, keeping row to row distance of 0.70m ,while plant to plant distance was 0.25-m.Standard cultural practices were applied including disease and pest management.Harvesting was performed after the grains reached maturity and plants were dried, at which grain moisture was determined.Data were recorded on DTT (Days To Tasselling), DTS (Days To Silking), plant height, ear height, ear length (cm), leaf area, leaves number per plant, cob weight, Ears number, TDM (Total Dray Matter), number of rows ear, number of kernel rows per row, 100-kernel weight (g) and grain yield /plant.Heterosis was estimated based on best parent.Analysis of variance was performed to detect differences among the maize entries using GENSTAT software.

Tasseling and Silking
The analysis of variance revealed that entries varied significantly (P ≤ 0.01) for days to 50% tasseling (DTT) and silking (DTS) (Table 1), where the hybrids were earlier than their parental inbred lines in both traits (Table 2).The mean overall of hybrids was 60.7 and 64.3 day for DTT and DTS respectively, while 64.4 and 69.2 day for inbreds.The analysis of single orthogonals showed a highly significant difference between hybrids and their parental lines in DTT and DTS (Table 1).The mean DTT ranged from 52 to 64 day and 60 to 69 day for hybrids and inbreds respectively, and the mean DTS ranged from 58-67 day and 66-73 day for hybrids and inbreds respectively.The earliest 3-way cross hybrid in DTT and DTS was TW7, while the latest 3-way cross hybrid was TW28.It is important to pay attention of tasseling-silking interval (TSI) in hybrids, where the success of parental lines in producing hybrid seeds depends on synchrony between DTT and DTS.The long period of TSI leads to higher probability of infertility, shrinkage kernels [8].The tasseling-silking interval (TSI) was about five days for hybrids and four days for inbreds, in spite of that the hybrids produced more kernels / row as compare to their parental lines (table 2).This could be attributes to higher viability of pollen grain for hybrids.Al-Fahdawii and Hamdalla [9] showed that pollen grains of maize hybrids own a longer longevity as compare to inbreds and synthetic cultivars.

Plant Height and Ear Height
Entries were highly significantly different for plant height and ear height (Table 1).Most hybrids exceeded their parental lines in both traits.Coefficient of variation for plant height and ear height were 2.0% and 2.85% respectively.Highly significant difference between hybrids and their parental inbreds has been occurred in plant height and ear height according to single orthogonals test (Table 1).Means of hybrids varied from 143 to 210 cm for plant height, and 69.9 to 120 cm for ear height.The average plant height and ear height for hybrids was 181.8 and 94.3 cm respectively, while was 143.2 and 69.1 cm for inbreds (Table 2).The taller hybrid was TW7 for both plant height and ear height (210 and 120 cm respectively).TW13 hybrid showed minimum plant height and ear height.[10] have got highly significant differences among maize 3-way crosses.The major factors of internode elongation in plant are solar radiation and temperature, in addition to the genetic potential, which be the reason of variation in plant height and ear height among the studied entries [11].

Leaves Area and Leaves Number
Highly significant differences have been found among the studied entries (P ≤ 0.01) for leaf area and leaves number (Table 1).The 3-way cross hybrids dominated on their parental inbreds in leaf area and leaves number based on single orthogonal analysis (Table 1).The hybrids override their parental inbreds in both traits, but the dominance was greatest in leaves number (Table 2).The mean overall of the hybrids was 0.53 cm2 and 13.3 for leaf area and leaves number respectively, while was 0.40 cm2 and 10.3 leaf for inbreds.The mean of leaf area ranged from 0.41to 0.76 cm 2 and 0.311to 0.49 cm2 for hybrids and inbreds respectively, and the mean of leaves number ranged from 11.94 to12.0 and 8.40 to12.48 leaf for hybrids and inbreds respectively.The hybrids TW7 and TW9 own highest leaf area (0.76 and 0.73 respectively), while TW5, TW6 and TW12 had highest leaves number (15.55, 15.46 and 16.0 respectively).Leaves are the major source for photosynthesis process, therefore leaves area and leaves number are the most contributes parts in metabolites production.Environmental conditions have minor impact on leaves number and considerable effect on leaves area.Anyway, the variations in both traits were obvious between hybrids and their parental inbreds.

TDM
Table 1 refers to significant differences among the studied entries for total dry matter (TDM), and also indicates highly significant difference between 3-way cross hybrids and their parental inbreds.Most hybrids surpassed their parental inbreds in TDM.Coefficient of variation was 1.49 and the average of hybrids varied from 185 to 381 gm which reflect the divergence among hybrids in this trait.The average of inbred lines varied from 201-261 gm (Table 2).TDM consider a good indicator for metabolites level in plant in exist of excellent potential for transformation these material to the sinks [12].

Ear Length and Ears Number
Analysis of variance showed highly significant (P ≤ 0.01) differences among hybrids for ear length and ears number.The analysis of single orthogonals showed a highly significant difference between hybrids and their parental inbreds in ear length and ears number (Table 1).All hybrids gave higher means for ear length and ears number over their parental inbreds (17.7 and 13.4 cm for ear length and 1.09 and 1 for ears number respectively).The hybrid TW10 gave the highest means for ear length (22.95 cm), and TW16, TW24 and TW25 gave the highest means for ears number (1.22-1.23).The W13 hybrid showed minimum mean for ear height, while 11 hybrids showed minimum ears number.

Ear Weight and Cob Weight
Entries were highly significantly different for ear weight and cob weight (Table 1).All hybrids exceeded their parental inbreds in both traits according to single orthogonal analysis.Coefficient of variation for was 1.62 % and 7.91% for ear weight and cob weight respectively.Means of hybrids varied from 117.2 to 256.8 gm for ear weight, and 19.57 to 36.5 gm for cob weight.The average ear weight and cob weight for hybrids was 186.7 and 26.4 gm respectively, while was 87.9 and 16.2 gm for inbreds (Table 2).The hybrid TW8 own highest mean for ear weight and cob weight (256.8 and 36.8 respectively), while TW13 and TW14 hybrids showed minimum mean for both traits respectively.The ratio of ear weight to cob weight was 7 and 5.4 for hybrids and inbreds respectively.This indicates a great potential of hybrids in transform the metabolites to the grains.

Rows Number/ Ear and Kernels Number/ Row
The hybrids differed significantly about their parental inbreds in rows number/ ear and kernels number / row (Table 1).The 3-way cross hybrids dominated on their parental inbreds based on single orthogonal analysis.The average rows number/ ear and kernels number / row for hybrids was 15.9 and 38.2, respectively, while was 13.5 and 27.1 for rows number/ ear and kernels number / row for inbreds respectively.The hybrid TW8 and TW7 own highest mean for rows number/ ear and kernels number / row (18.5 and 45.8), whileTW13 and TW14 showed minimum mean for both traits (12.6 and 30.7 respectively).

100 Kernels Weight
Table 1 refers to significant differences among the studied entries for 100 Kernels weight, and also indicates highly significant difference between 3-way cross hybrids and their parental inbreds.Most hybrids surpassed their parental inbreds in 100 Kernels weight, and the average of hybrids varied from 98.2 gm for hybrid TW6 to 68.6 gm for hybrid TW9 with overall mean 78.7 gm which reflect the divergence among hybrids in this trait.The average of inbred cross hybrids varied 17.4 -24.1 gm with overall mean 19.9 gm (Table 2).

Grain Yield/ Plant
Analysis of variance showed highly significant (P ≤ 0.01) differences among entries for grain yield/plant in favor of the 3-way cross hybrids according to single orthogonal test (Table 1).All hybrids gave higher means for grain yield/plant over their parental, which ranged from 95 gm for TW13 to 219 gm for TW8 with overall mean 159.8 gm, while it was 71.6 gm for inbreds.
Table 1.Analysis of variance due to mean square for yield and related traits of three way crosses evaluated and five inbred lines.

Heterosis
Heterosis is the excess in size, growth, fertility, yield and resistance to biotic or a biotic stresses in offspring compared with their inbred parents [13] .The extent of heterosis provides information on scope of genetic variety of parents in developing superior offspring to utilize hybrid vigor and has direct effect on the breeding methodology [14] .Heterosis is an efficacious tool for exploitation the potential of inbreds and this depends on the direction and amount of heterosis and also the type of gene action [15].Table 3 refers to the amount of heterosis for each hybrid.TW8 and TW10 hybrids possess the highest amount of hybrid vigor for five traits, while TW7 and TW1 owned highest amount of hybrid vigor for four and three traits respectively.TW13 hybrid produced negative amount of hybrid vigor for four traits, while TW15 and TW18 hybrids gave negative amount of hybrid vigor for three traits.Some hybrids did not produce hybrid vigor (zero).The interesting point is that there are some hybrids gave highest amount of heterosis for some traits and in the same time did not give a negative or zero of heterosis for other traits such as TW8 and TW10.This indicates to the high genetic potential of these hybrids at genome level.The high degree of heterosis for some hybrids may be a result of having their parental lines some complementary genes for each other, leading to get a considerable hybrid vigor.According to [16] the aspect of heterosis relates on the extent of genetic diversity of two parents, and the genetic divergence of the parents is deduced from the heterotic patterns through a series of cross combination [17].

Conclusion
The current study defined some outstanding 3-way cross hybrids maize genotypes owing yielding potential.The average grain yield for hybrids ranged from 95 to 219 gm/plant.The hybrids TW8 and TW10 were most outstanding for grain yield, which gave 219 and 214 gm/plant respectively, and positive heterosis over best parents which reached 72 and 62% respectively.Also, the promising hybrids, which showed high heterosis for grain yield and related traits, need to be tested in farmer fields across multi-sites trials along of commercial checks and OPVs for its validity of the performance and stability, and subsequently use these hopeful hybrids in futurity breeding programs.

Table 2 .
Mean values of yield and related traits of three-way maize hybrids and their parents

Table 3 .
Estimates of standard heterosis for yield and related trait of three way hybrids maize based on best parental inbred lines.