Inheritance Pattern of Earliness and Yield Related-Traits in Spring Barley ( Hordeum vulgare L . )

To understand the genetic patterns of the physio-morphological traits for barley grain yield, six-generations (P1, P2, F1, F2, BC1, and BC2) were used to determine the type of gene action in the four barley crosses. Grain yield showed a strong positive association (r = 0.83 and 1) with Grain Filling Rate in Giza121/RIL1 and Giza126/RIL2 crosses, respectively. The relationship between yield and earliness was not consistent with crosses and positive (r) values were quite low. It should be possible to select early-maturing and high-yielding segregates with high 100kernel weight. The results indicated that the dominance effect [dd] was more important and greater than the additive effect [aa] and [ad] for most traits. Positive heterosis over the midand betterparent was quite similar for the most traits, except for heading and maturity dates, that showed negative heterotic effects. The inbreeding depression was high significant and positive for Grain Filling Rate, chlorophyll contents, Flag Leaf area and 100kernel weight. On the other hand, it was a negatively significant for the earliness trait (HD, MD, and GFP). The lack of uniformity for estimates of inbreeding depression can be explained by environmental variation and to its influence on the type of gene action. Narrow-sense heritability ranged from 13.3% for Grain Filling Period in Giza12/RIL1 to 66.6% for heading dates in Giza121/RIL2 crosses. Genetic advance estimates were low due to lack of additive variance. The crosses Giza121/RIL1 and Giza126/RIL2 would be of interest in a breeding program, for improving characteristics of earliness, yield, and its components.


Introduction
Barley (Hordeum vulgare L.) is a crop with great adaptive potential in many regions of the world.In areas which have only a brief rainy season, growers can obtain a harvest mainly because this crop has advantages in aspects such as salt tolerance, frost tolerance in the early period of development, drought tolerance, etc. Breeding for quantitative traits in early generations is impeded by several factors such as polygenic nature and low heritability of a trait (grain yield, the number of spikes per plant, etc.), linkage, non-additive gene effects and environmental effects (Harlan, 1976).
In order to overcome these difficulties, it is necessary to get as much information as possible about the genetic structure of breeding population undergoing selection (Sharma et al., 2003).This means identifying the gene effects that control the inheritance of a trait of interest and contributing to the exploitable genetic variance of the population.
According to (Falconer & Mackay, 1996) heritability is defined as the measure of the correspondence between breeding values and phenotypic values.Thus, heritability plays a predictive role in breeding, expressing the reliability of phenotype as a guide to its breeding value (Addisu et al., 2015).There is a direct relationship between heritability and response to the selection, which is referred to as genetic advance.High genetic advance with high heritability estimates offers the most effective condition for selection (Yadav et al., 2015).The value of heritability, therefore, increases when it is used to calculate genetic advance, which indicates the degree of gain in a characteristic obtained under a particular selection pressure.Thus, genetic advance is another important selection parameter that helps breeder in a selection program.Moreover, most agronomical important traits, including grain yield, have complex genetic inheritance and require the use of relatively large populations for studying plant breeding.In self-pollinating, segregating populations, the frequency of individuals with all favorable alleles is reduced with generation advance (Addisu & Shumet, 2015).
The present study is seeking to estimate the type of gene action, heterosis, heritability, and genetic advance on the base of individual segregating populations for grain yield, earliness and some physiological characteristic in spring barley.

Experimental Site
The field experiment was conducted at the Experimental Farm of Sakha Agricultural Research Station 31.3°N,30.9°E,Agricultural Research Center (ARC), Egypt during three winter seasons.The experimental soil was clayey, pH 8.2 and organic matter content in the soil was about 1.4%.The average annual rainfall of the region was 180 mm during the growing season.

Germplasm
Four six-row spring barley genotypes were used in this investigation; Giza121 and Giza126 are Egyptian cultivars with good agronomic characteristics; maturity 136 and 144 days, respectively; susceptible to powdery mildew and leaf rust.The RIL1 and RIL2 lines were introduced from The International Center for Agricultural Research in the Dry Areas (ICARDA) and exhibit height, stiff straw strength, early maturity, resistant to stem rust and moderately to powdery mildew (Table 1).The differences among the parents had been determined using Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) (Laemmli, 1970).
Table 1.Production of backcross progenies from the four crosses.
In 2009/10 season; seeds of the, F 1 's were sown to produce, F 1 plants.Each of F 1 plants was crossed back to their respective parent to produce first correspondent backcross BC 1 and BC 2 .In the meantime, the four parents were re-crossed to produce the F 1 's seeds.However, F 1 Plants not used in backcrosses were self-pollinated to produce F 2 seed (Figure 1).
Figure 1 In 2010/11 grown tog ensure acc of 17 rows The expec ∆g = K × √ addition, t as follows

The M
The molec that the mo

Note. The downward
The mean  liers.de the Concerning the phenotypic correlation coefficients, the results although many rather small correlation coefficients are statistically significant, r values below 0.4 have little practical significance because they indicate the relationship between the two characteristics accounts for only a GFR of the total variation.High yielding segregates with high kernel weight can probably be selected since r values were almost always positive.The results of correlation analysis among the eight traits are shown in (Table 3).The FL was significantly and positively correlated (P ≤ 0.01) with GFR and GY in C1; HD and GY in C2; GFR with KW and GY in addition, KW and GY in C3 and GFR with FL and GY, plus FL and GY in C4, indicating that FL, GFR, and KW was associated with GY/plant.Note.HD: heading date; MD: maturity date; GFP: Grain filling period; GFR: grain filling rate; Ch: Chlorophyll content; FL: flag leaf area; KW: 100-karnels weight (g); GY; grain yield (g/plant).C1: Giza121/RIL1; C2: Giza121/RIL2; Giza126/RIL1; Giza126/RIL2.* and **: significant and highly significant at 95% and 99% probability levels, respectively.

Mode of Gene Action
The results of the six-parameter model and type of epistasis revealed the presence of a non-allelic interaction for most studied characteristics in the most studied crosses except for C4 cross in Ch and GY that indicated the absence of a non-allelic interaction (Table 4).It is worthy to mention that at least one of the A, B and C tests was significant for the previous characteristics, indicating adequacy of the six-parameter model to explain the type of gene action controlling the traits in these crosses.Additive gene effects [a] were quite small in magnitude relative to the dominance gene effects.Significant or highly significant positive additive gene effects [a] were obtained for HD in the C3 and C4 crosses, MD in the C1, C3 and C4 crosses, and all crosses for FL.On the other hand, it was negative significant for HD and MD in C2; GFP in C1; GFR in C3 and C4; Ch in all crosses except for C1.The major contribution by dominance [d] effects to variation in C2, C3 and C4 crosses in all traits except for GFR and FL.

Heterosis, Inbreeding Depression and Potence Ratio of the F 1 Hybrids
Estimates of heterosis are specific to each particular cross and are affected by the environment (supplemental Table 2).The genes by which two lines differ will not be the same for all pairs of lines, so different pairs of lines will have different values and will show different amounts of heterosis.The heterosis of MD% was quite similar among crosses to HD, but there was essentially no heterosis over the high parent.Positive highly significant heterosis over mid-parent in most crosses was detected in most studied traits except for HD, MD, and GFP (Figure 5a, 5b, 5c, and 5d).Note.HD: heading date; MD: maturity date; GFP: Grain filling period; GFR: grain filling rate; Ch: Chlorophyll content; FL: flag leaf area; KW: 100-karnels weight (g); GY; grain yield (g/plant).C1: Giza121/RIL1; C2: Giza121/RIL2; Giza126/RIL1; Giza126/RIL2.* and **: significant and highly significant at 95% and 99% probability levels, respectively.

Inbreeding Depression
ID% was less consistent for KW and GY/plant (supplemental Table 2).The lack of uniformity for estimates of inbreeding depression can be related to environmental variation and to its influence on types of generation (Figure 5).The estimated values of potence ratios (PR%) illustrated that in most F 1 crosses the estimated PR% had a positive nature for the characteristics of GFR, FL, KW and GY/plant.These results reflected, generally, various degrees of dominance, i.e., partial-to over-dominance, which is involved in the inheritance of these characteristics.On the contrary, the estimated values of potence ratios in most F 1 hybrids were negative for HD, MD, and GFP.Negative values of PR% indicated the presence of various degrees of recessiveness, i.e., partialto under-recessiveness.PR% had negative nature for all evaluated F 1 hybrids for HD and ranged from -0.18 to -9.28.These results indicated the presence of partial-to over-dominance, which is involved in the inheritance of jas.ccsenet.
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Discussion
Selection of the appropriate parents to be used in artificial crosses is one of the main decisions faced by plant breeders that will facilitate the exploitation of maximum genetic variability and production of superior recombinant genotypes, so selecting the parents based on the molecular variation can take into account with high phenotypic variation in the traits under study.One-dimensional SDS-PAGE electrophoresis analysis (Laemmli, 1970) separations are shown in (Figure 2), the analysis shows that the most variance between the parents was in prolamin fractions (hordeins), and that mean the parents which used in this study were abroad-relative.
The yield performance results for the six-populations suggest that late heading is dominant to early heading, Moreover, the 100-KW and GY of F 2 and backcross populations were considerably higher than the best parent, which indicates a high heterotic effect (Abd El-Aty et al., 2011).The morphological and phenological evaluation of barley is necessary to determine their importance on grain yield increase.Therefore, grain number per spike and grain weight is the other important yield components that affect grain yield (Yadav et al., 2015).The current results explained the four crosses' traits were quantitatively inherited and could be controlled by multiple genes (Zhang et al., 2015).

Phenotypic Correlation Coefficients
The relationship between yield and heading date was not consistent from the cross to another and the r values were quite low, indicated the importance of these traits in yield improvement and would be considered in selection program (Table 3).In barley, the importance of flag leaf in determining grain yield was also intensively studied (Xue et al., 2008).Teng et al. (2004) reported that leaf chlorophyll content was positively correlated with photosynthetic capacity and high chlorophyll content as a favorable trait in rice production.Besides grain yield, which represents the ultimate selection objective, a number of yields-related traits have received much attention, such as chlorophyll content, flag leaf area, days to heading, plant height, 1000-kernel weight and grains per spike in spring barley by Teng et al. (2004) andAbd El-Aty et al. (2011).

Types of Gene Action
The major contribution by dominance [d] effects to variation in C2, C3, and C4 crosses in all traits except for GFR and FL, which were indicated by the relative magnitude of the parameter [d] to the parameter [m].A significance of [a] and [d] components indicated that both additive and dominance gene effects were important in the inheritance of these traits and selecting desirable traits would be effective in the late generations (Gamble, 1962;Abd El-Aty et al., 2011).Highly positive significant for additive × additive [aa] effects were detected for; KW in C3 and C4; GY in C2, while negative significant effects for [aa] type was found for HD in C1 and C3, MD in C2, FL in C3, Ch in C3 and KW in C2. Mulbah et al. (2015) have found that additive gene effects make a greater contribution to the total genetic variation than the estimates obtained in his study on rice.The absolute relative magnitudes of the epistatic gene effects to the mean effects are somewhat variable depending on the cross.In some crosses, notably, Giza121/RIL2 and Giza126/RIL1 in most traits, the absolute magnitude of the epistatic gene effects are larger than the mean effects and come up to that of the dominance effects.
Duplicate epistasis was observed, as revealed by differences in signs of [d] and [dd] in crosses, which exhibited significant epistasis, while similar signs of [d] and [dd] in complementary epistasis.Complementary epistasis was prevailing in C3 and C1 crosses for HD and MD, respectively.the C1, the C2, and C4 crosses in LA, the C3 and C4 crosses for KW, which coincide with the results obtained by Sharma et al. (2003).These findings illustrated that duplicate epistasis was prevailing for most traits (Yadav et al., 2015).Chaudhary et al. (1974) detected that the epistatic duplicate type was predominant over the complementary type.

Heterosis
Yield in barley, like in other crops, is a very complex trait and is a result of the interaction between various yield components and the environment.Knowledge of the association between yield-related traits is of immense importance to the selection of desired combinations of characteristics Zhang et al., (2015).Heterosis led to a considerable increase in total biological yield, grain yield and straw yield (Finlay & Wilkinson, 1963;Amer et al., 2012a).The relative effect of Heterosis clearly depended on the genetic background, crosses between genetically divergent or non-adapted materials led to a higher relative effect of Heterosis than crosses among related or adapted materials (Abd El-Aty et al., 2011).Yield, as well as yield components, is determined by several genes, with specific interactions that make breeding for yield increase more difficult.Different degrees of gene effects, i.e., partial to over-dominance, were clear to be involved in the inheritance of FL, KW and GY/plant (Abd El-Aty et al., 2011;Elakhdar et al., 2016a).
Heritability values indicate the degree of genetic relationship between the performance of parents and progeny which is an important aspect for obtaining genetic progress on artificial selection.The broad sense heritability for GY and the earliness characteristic in all crosses were considerably larger than the corresponding narrow sense estimates (Addisu & Shumet, 2015).Very low narrow sense estimates were obtained for Giza126/RIL2, which means the expected response to selection from these populations generally low.Esparza Martínez and Foster (1998) reported that grain weight is a relatively stable yield component in barley.Hence, selection for traits phenological shows the higher variation in all conditions is more effective and having appropriate heritability.The predicted genetic advance estimates were low to moderate for all studied traits and ranged ranging from 2.05% for MD in C4 to 51.17% for FL in C2.These results indicated the possibility of practicing selection in early generations and obtaining high yielding genotypes (Abd El-Aty et al., 2011).Therefore, the selection in the present those particular populations should be effective and satisfactory for successful breeding purposes.The dominance effects (σ 2 D) were greater than those of additive effects (σ 2 A) for most studied traits (Supplemental Table 3), indicating that the selection for these traits might be non-effective in early generations to improve such traits in the four studied crosses (Addisu & Shumet, 2015).The estimate of genetic advance (Δg %), which evaluates the expected rate of genetic gain under directional selection, was inconsistent among crosses and in some cases it was zero due to the lack of additive variance.
It can be concluded that the degree of improving the studied traits was successfully based on the high heritability values and positive additive genetic advance shown by the different traits, especially; KW and GY as was reported by Aidun et al. (1990) and Yadav et al. (2015).Generally, the most biometrical parameters resulted from the first and the third cross (Giza121/RIL1 and Giza126/RIL2) were found to be higher in magnitude in comparison with those from other crosses.Consequently, it could be concluded that the above-mentioned crosses would be of interest in breeding programs for improving traits for earliness, yield, and its components.

Conclusion
Because of the need for harvesting and threshing of individual plants, the grain yield is difficult to quantify.Therefore, indirect selection strategies for less complex traits, with higher heritability and good correlation with grain yield, may facilitate the selection in generations with high levels of heterosis.The chlorophyll content and flag leaf are one of the greatest components in determining grain yield potential in barley.So that, effective selection in plant breeding is based on information about the extent to which observed differences in the traits under selection are highly heritable and the extent to which they are correlated with each other and also with GY.

Figure
Figure arrow track in d, C-hordeins 5

Table 3 .
The correlation coefficients among eight traits of the F 2 population

Table 4 .
Scaling tests and gene effects estimates for all studied traits in the four crosses