ESTIMATION OF HERITABILITY AND GENETIC ADVANCE FOR VARIOUS METRIC TRAITS IN SEVEN F2 POPULATIONS OF BREAD WHEAT (TRITICUM AESTIVUM L.)

Heritability estimates provide information about the traits that are transmitted from parents to their offsprings and it has a crucial role in selection criteria to improve grain yield. The purpose of the present study was to compute heritability and genetic advance of seven F2 populations derived through cross combinations of five parental varieties/lines of bread wheat Iqbal-2000, Lasani2008, 9444, 9432 and 9436. Data were recorded for seven metric traits: plant height, days to heading, flag leaf area, peduncle length, number of kernels per spike, kernel weight per spike and grain yield per plant. The estimates of heritability were low to high for all the traits studied except for kernel weight per spike which had a moderate to high value of heritability. Results depict that all the mentioned traits can be enhanced easily due to high values of heritability and phenotypic variations. The cross combinations 9436 × Iqbal-2000 and 9436 × Lasani-2008 had high heritability for most of the traits. Therefore, selection could be practiced among wheat crosses with special emphasis on crosses, namely 9436 × Iqbal-2000, to improve grain yield per plant.


Introduction
Wheat (Triticuma estivum L.) is one of the major crops of the whole world.A wheat crop has a central position in the policy making of Pakistan.Wheat is a top priority crop for farmers in Pakistan and it also contributes 10.1% in value added in agriculture and 2.2% in overall GDP (Economic survey of Pakistan, 2014).It is named as a 'king of cereals' because of its nutritional value, production and demand.
Heritability estimates drive the breeding program toward genotypic variances that are influenced by phenotypic variances.It provides information about the Babar Saleem et al. 2 structure of population and the percentage of trait transmission from one generation to the next.The higher value of heritability will make the selection process effective, which will result in higher response.Heritability studies help the plant breeder to predict about the interaction of genes in successive generations and are essential for effective breeding programs.Hence, heritability estimates in this study would help to predict about the possible progress that can be attained by making the selection process effective.Moreover, genetic advance estimates give a clear picture of segregating generations to make selection effective.Kisana et al. (1982) studied five wheat crosses and proved high heritability and genetic advance for plant height and grain yield.Das and Rehman (1984) recorded high heritability for grains per spike and grain yield.Haq et al. (2008) observed high heritability and genetic advance in grains per spike and grain yield per plant.Kahrizi et al. (2010) studied 12 advanced durum wheat cultivars and two checks and found high heritability for plant height and peduncle length.Gulnaz et al. (2011) recorded high heritability and genetic advance (80%, 11.28, respectively) for plant height.Ullah et al. (2011) noted high heritability for plant height and days to heading.Ijaz et al. (2013) reported high heritability and genetic advance for plant height, flag leaf area, 1,000-grain weight, number of tillers per plant and grain yield per plant.This study is aimed to estimate variability and genetic parameters for yield and other agronomic characters.These values will help in making effective selection for the improvement of characters under study.

Material and Methods
The experimental material was comprised of seven F 2 populations involving five cultivars of bread wheat as parents: Iqbal-2000, Lasani-2008, 9444, 9432 and9436.The experimental material was planted in the research area of the Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, in December 2011.Seeds of F 2 progeny and parents were grown in lines with the help of dibbler, keeping plant to plant distance at 15cm and row to row distance at 30cm.Two seeds per hole were sown and were later thinned to one healthy seedling per hill after germination.All the crop protection measures were adopted on time.Precautionary measures were adopted to avoid contamination of the experimental material.The F 2 progenies studied were 9432 × 9436, 9432 × 9444, 9432 × Iqbal-2000, 9432 × Lasani-2008, 9436 × Iqbal-2000, 9436 × Lasani-2008and Iqbal-2000 × 9444.Data were collected for plant height, days to heading, flag leaf area, peduncle length, number of grains per spike, grain weight per spike, 100-kernel weight and grain yield per plant.At maturity, two hundred healthy and competitive plants from the F 2 population of each cross and 20 plants from each parent were taken at random and data were recorded and analyzed.Means, variances, and coefficient of variation were calculated as indicated in Table 1.Broad sense heritability in percentage was measured by using the formula as proposed by Mahmud and Kramer (1951): where: h 2 (broad sense heritability), VF 2 (variance of F 2 population),VP 1 (variance of parent 1) and VP 2 (variance of parent 2).
Genetic advance (GA) (absolute) was computed using the following formula proposed by Allard (1960) as under: .
where: GA (genetic advance), σρ (phenotypic standard deviation of F 2 population), h 2 (broad sense heritability in fraction) and i (a constant value that reflects the selection intensity.The value used for i in this study at 10% selection intensity was 1.755).

Plant height (cm)
Plant height is one of the important characters that determine the yield along with other characters.The short stature of wheat plants was responsible for the green revolution.It is obvious from Table 1 that the cross 9432 × 9436 has a high value of variance (94.84) and coefficient of variability (9.30%).These parameters suggest that considerable variation for plant height exists in populations under study.In the F 2 populations, mean plant height ranged from 89.30cm (9436 × Lasani-2008) to 106.80cm (9432 × 9444).Among the parental genotypes, average plant height varied from 85.93cm (9436) to 109.20cm (9444).The heritability estimates ranged from 10.08% to 92.80%.The highest heritability and genetic advance were recorded in the cross 9432 × 9436 (92.80% and 15.86, respectively).The cross 9432 × Iqbal-2000 showed the lowest heritability (10.08%) and the lowest genetic advance (0.68).It is clearly shown in Table 2 that high heritability and genetic advance indicated the presence of genetic variability among the F 2 populations for plant height and different height levels can be chosen from these crosses.The present results authenticate the research work of Khadr (1971), Teich (1984), Chowdhry et al. (1997) and Yadav et al. (2011).

Days to heading
Days to heading is an important yield contributing trait.It is clear from Table 2 that days to heading showed low to moderate values of heritability.The highest value (77.06%) was obtained for the cross combination 9436 × Iqbal-2000 followed by 9432 × Lasani-2008 (72.25%).The lowest estimate of heritability (4.75%) was observed for 9432 × 9444.The estimates of genetic advance ranged from 0.14 to 3.72 for the crosses 9436 × Iqbal-2000 and 9436 × Iqbal-2000, respectively.These results suggest that improvement in this trait is possible through intelligent selection in early generations.Similar results were also reported by Khadr (1971), Nanda et al. (1981) and Subhani et al. (2000).Flag leaf area (cm 2 ) Flag leaf area has an indirect effect on grain yield of the wheat plant.The greater the flag leaf area, the greater will be the rate of photosynthesis as the plant can harness more energy from sunlight (Ijaz et al., 2013).
In the F 2 populations, maximum flag leaf area (31.38 cm 2 ) was noted in the cross 9436 × Lasani-2008.Variances ranged from 8.43 to 18.58 indicating the existence of variability for this trait.Heritability estimates for this trait were moderately high.A high heritability value of 88.05% was recorded in the cross 9432 × 9444 followed by the cross Iqbal-2000 × 9444 (78.44%).The lowest heritability estimate (46.62%) was observed for the cross 9436 × Iqbal-2000.The estimates of genetic advance ranged from 2.46 (9436 × Iqbal-2000) to 6.58 (9432 × 9444).High heritability and genetic advance estimates show that this trait can be improved through sensible selection among these crosses.The results of the present research are in agreement with the findings of Chowdhry et al. (1997), Khan et al. (2003), Ahmed et al. (2004) and Farooq et al. (2011).

Peduncle length (cm)
Peduncle length determines grain yield along with spike length and spike density.The highest value for peduncle length was obtained for Iqbal 2000 × 9444 (28.19 cm).Heritability and genetic advance for peduncle length ranged from 31.02 to 85.39 and from 1.27 to 4.40, respectively.The highest value of heritability was obtained for 9436 × Lasani-2008 (85.39 %) coupled with a high value of genetic advance (4.40).A considerable amount of variation for this trait was also observed.All the genetic parameters give a clear indication that this trait can be used as selection criterion.Improvement is possible through careful selection in early generations.These results are also supported by the findings of Subhani et al. (2000) and Khan et al. (2003).

Number of grains per spike
The number of grains per spike is also an important plant attribute that depends upon head length, spikelets per spike and spike density.However, grains per spike can be useful only when there is proper grain formation in the florets.Hence, a selection procedure must focus on this trait for enhancing grain yield per plant.High values for CV percentage and variance were 10.07% and 32.34%, respectively.These estimates indicate the presence of sufficient variability for this trait.Heritability values ranged from 23.31% to 76.40%.The highest values of heritability and genetic advance were obtained for the cross combinations 9432 × Iqbal 2000 and 9432 × 9444, respectively.High heritability and genetic advance show that fruitful selection for this trait is possible.Similar findings have also been reported by Mahmood and Shahid (1993), Salim et al. (2003), Ali et al. (2010) and Zecevic et al. (2010).

Grain weight per spike (g)
Grain weight per spike is a character of vital importance and of special interest to a wheat breeder.Higher estimates for heritability and variability are important for the wheat breeder to choose promising cross combinations and to attain the maximum level of yield potential.Among the F 2 populations, the highest value of 2.28g was observed in the cross 9432 × Iqbal-2000 which is higher than a parental value.Variance and C.V ranged from 0.05 to 0.14 and from 10.40 to 18.81, respectively, which shows the presence of a considerable amount of variability for grain yield per plant.The highest values of heritability (88.24%) and genetic advance (0.63%) were obtained for the cross 9436 × Lasani-2008, which shows that grain yield per plant can be improved through selection.The obtained results are in conformity with the research findings of Khadr (1971), Teich (1984), Chowdhry et al. (1997), Ansari et al. (1999) and Rashidi (2011).
Grain yield per plant (g) Grain yield per plant is a character of chief importance and of special interest to a wheat breeder.Higher estimates for heritability, genetic gain and variability would be important to a wheat breeder to choose promising cross combinations and to attain the maximum level of yield potential.

Conclusion
Ključne reči: Triticum aestivum, heritabilnost u širem smislu, genetski napredak, metričke osobine, pšenica.* Autor za kontakt: e-mail: m.talha.shahzad@gmail.com It is clear from the results that cross combinations 9432 ×Iqbal-2000 , 9436 ×  Iqbal-2000, 9432 × 94444  possess high values of genetic parameters for vital yield component traits such as flag leaf area, number of grains per spike, grain weight per spike and grain yield per plant.Improvement through effective and intelligent selection is possible.Therefore, it is suggested to give due consideration to these cross combinations and parent genotypes in a further breeding program.PROCENA HERITABILNOSTI I GENETSKOG NAPRETKA ZA RAZLIČITE METRIČKE OSOBINE KOD SEDAM F 2 POPULACIJA HLEBNE PŠENICE (TRITICUM AESTIVUM L.)

Table 1 .
Means (x), variances (V) and coefficients of variability (CV) for various metric traits in bread wheat.

Table 2 .
Heritability (h 2 ) and genetic advance (GA) for various metric traits in bread wheat.