Heritability estimates in F 4 generation of wheat ( Triticum aestivum L . ) under the agro-climatic condition of Tandojam , Sindh-Pakistan

The research studies on heritability estimates were conducted to evaluate the performance of grain yield and various yield components of six F4 segregating population originated from four parental varieties of bread wheat. The experiment was conducted in Randomized Complete Block Design with 3 replications. The results for six F4 segregating populations and their four parental wheat varieties for the traits revealed highly significant differences at P< 0.01 and P< 0.05 level of probability. Different progenies showed different response for different traits. The progeny Sarsabaz x Bhittai took significantly more days to 75% maturity (128.3), more spike length (14.0 cm) and more spikelets spike (21.6). Progeny Sarsabz x FD-83 showed significant increase in grain yield plant (29.0g), 1000-grain weight (48.0 g) and tillers plant (13.67) as compared to other progenies and the parental lines. The parent varieties Sarsabaz and Bhittai showed good performance with respect to number of tillers plant (15.33) and spikelets spike(24.3). The progeny FD-83 x Bhittai revealed significant in number of grain spike (56.7) and biological yield kg ha (22960) as compared to their respective parental lines. Two progenies Nesser x Bhittai and Nesser x FD83 showed the highest heritability coupled with more genetic advance (GA) for most of the traits measured i.e., days to 75% maturity, spike length, grains spike and grain yield plant. Four progenies viz., Sarsabaz x Bhittai, FD-83 x Bhittai, Sarsabz x FD-83 and Nesser x Sarsabz showed better performance highest heritability associated with high genetic advance for other characters tillers plant, spikelets spike,1000-grain weight and biological yield kg ha. These results suggest that more effective selection could be obtained from these segregating populations for specific traits originated after these combinations.


Introduction
Bread wheat (Triticum aestivum L.) belongs to family Poaceae (grass family) is a staple food for billions of people in the world.The most spread and cultivated species of wheat is Triticum aestivum (hexaploid) and the most used variety of wheat currently is Triticum durum (tetraploid).The other wheat species like Tritcum dicoccum and Triticum spelta are also cultivated in less quantity [1].To feed the ever-increasing population in the country, the need for more wheat will continue.There are enough possibilities to increase wheat yields in Pakistan through developing new high yielding varieties and by adoption of proper package of technology [2, 3].However, if a character or trait is controlled by non additive gene action it gives high heritability but low genetic advance, while the character ruled by additive gene action, heritability and genetic advance both would be high [4].Heritability values can be used as a measuring scale to determine genetic relationship between parents and progeny.Better heritability values recorded points to the possibility of improvement in the parameters therefore attention may be focused on important traits while synthesizing genotypes.It is also necessary that the extent of association between the important characters be worked out which would serve as a basic for selection in segregating generation.Heritability estimates reported by several workers including [5-7], indicated that certain components of grain yield in wheat are more heritable than yield itself.Ansari [8] have also estimated heritability parameters for yield and yield related traits of the wheat in the segregation populations.This suggested most likely that heritability is due to the additive genetic effects and selection could be effective in early segregating generations for these traits and the possibility of improvingS durum wheat grain yield through direct selection for grain yield related traits.Similar findings have been reported by Dwived et al. and Yousaf et al. [9,10].Using path coefficient analysis, it is easy to determine which yield component is influencing the yield substantially. Having this information, selection can then be based on that criterion thus making possible great progress through selection.

Materials and methods
The experiment was carried out at the Experimental Farm of Nuclear Institute of Agriculture (NIA), Tandojam during Rabi season 2011-12.Wheat breeding material for research work consisted of six F4 populations of bread wheat (Triticum aestivum L.) along with their four parental lines were evaluated under field conditions.Heritability in broad sense was estimated as suggested by Gardener (1961)

Results
Wheat breeding material for research work consisted of six F4 populations of bread wheat (Triticum aestivum L.) along with their four parental lines.The observations were recorded on grain yield plant -1 and its associated traits to evaluate genetic potential of the F4 populations.

Analysis of variance
Results suggested that the genotypes (parents and segregating progenies) were significantly (P ≤0.05) different with each other for most of the traits studied under present studies.Mean squares from ANOVA of six F4 segregating populations and their parental lines for the traits viz., number of tillers plant -1 , days to 75% maturity, spike length (cm), number of spikelet spike -1 , number of grains spike -1 , 1000-grains weight (g), grain yield plant -1 (g) and biological yield kg ha -1 were highly significant at P ≤ 0.01 level of probability (Table 1 & 2

Tillers plant -1
The data regarding the trait number of tillers plant -1 of the wheat varieties is depicted in Table 4.The parental line Sarsabz produced significantly the highest number of tillers plant -1 (15.3) as compared to all other parent varieties and F4 progenies; whereas, the minimum number of tillers plant -1 (8.67) was recorded in parental line FD-83.All the progenies and parent variety Nesser had produce more number of tillers and the difference among them was non-significant.

Spike length (cm)
Several wheat breeders have reported that spike length is quantitatively inherited and exhibited transgressive segregation with high heritability.(Rajper et al., 1990) found a low estimate for spike length.Moderate heritability values recorded could be an indicative of improvement in spike length.
The mean performance for spike length is given in (Table 4) showed that maximum spike length was (14.0cm) were produced by progeny Sarsabz x Bhittai; whereas minimum spikes (10.67 and 11.0 cm) were produced by parental lines Sarsabz and Nesser respectively.

Spikelets spike -1
The number of spikelets spike -1 depends upon spike length and spike density.The mean performance for spikelets spike -1 and it is represented in Table 4 showed that maximum number of spikelets spike -1 was (24.3) were observed by parental line Bhittai; whereas, minimum number was recorded in Nesser, FD-83, Sarsabz and progenies FD-83 x Bhittai and Nesser x FD-83.

Grains spike -1
The mean performance for grains spike -1 and it is represented in Table 4. Significantly the highest number of grains (56.3) was produced by the progeny FD-83 x Bhittai and lowest grains were produced by parental line Nesser (27.6).

1000-grain weight (g)
The trait 1000-grain weight is a main yield contributing trait.The mean performance for 1000-grain weight and it is represented in Table 5, wheat genotypes ranged between (37.0 to 48.0g).The highest 1000-grain weight recorded in Sarsabz x FD-83 followed by Nesser x FD-83 and Sarsabz x Bhittai.
Grain yield plant -1 (g) Genotypes showed significant differences (p<0.05)among each other for the main trait final yield.The result of mean performance in Table 5 for the trait grain yield plant -1 .
The progeny Sarsabz x FD-83 showed significantly the highest grain yield plant -1 (29.0 g) as compared to other genotypes.The lowest grain yield plant -1 (13.0g) was observed in progeny FD-83 x Bhittai.

Biological yield (kg ha -1 )
The result of mean performance in (Table 5) for the trait biological yield skg & kg ha -1 indicated the significant difference between F4 progenies and their parental lines.Result indicated that five progenies except Sarsabz x Bhittai had significant increase in their dry mater weight (biological weight) than all the parental varieties.

Grain yield plant -1
The mean performance for grain yield plant - 1 and it is represented in (Table 9).The character grain yield plant

Discussion
The result obtained regarding heritability parameters for grain yield and its important yield components present as under.
The combined analysis of variance for all the genotypes (including four parents and their six F4 progenies) depicted that both the parents and segregating populations differed significantly at P> 0.01 for most of the characters understudy, indicating the existence of great genetic variability among the genotypes (Table 1).The ANOVA for all the traits of six F4 segregating populations are summarized in (Table 1 & 2).Results suggested that the genotypes (parents and segregating progenies) were significantly (P ≤0.05) different with each other for most of the traits studied under present studies.Mean squares from ANOVA of six F4 segregating populations and their parental lines for the traits viz number of tillers plant -1 , days to 75% maturity, spike length (cm), number of spikelets spike -1 , number of grains spike -1 , 1000-grains weight (g), grain yield plant -1 (g) and biological yield plot -1 and kg ha 1 were highly significant at P ≤ 0.01 level of probability.
The mean performance for days to 75% maturity is given in (Table 1) and ANOVA is represented in ( The data regarding the trait number of tillers plant -1 of the wheat varieties is depicted in (Table 4), whereas mean square analysis of variance is represented in (Table 1).The results indicated significant differences among progenies at P≤0.01.The results showed that maximum number of tillers plant -1 was produced by parental line Sarsabz (15.3) as compared to all other parent varieties and F4 progenies; whereas, the minimum number of tillers plant -1 (8.66) was recorded in parental line FD-83.All the progenies and parent variety Nesser had produce more number of tillers and the difference among them was non-significant.Memon et al. [13] reported that the expression of the trait number of tillers depends on its genetic control in their present hence transgressed to their hybrids.Thus it may be inferred that selection for number of tiller plant -1 would be effective.
The results of this study corroborate with those of the findings of Mahmood and Shahid [14].
The mean square of ANOVA in (Table 1) showed significant difference among the six F4 progenies and their 4 parental lines of wheat for various traits.The mean performance in (Table 4) showed that maximum spike length was (14.0cm) in Sarsabz x Bhittai; whereas minimum spike length with (10.67 and 11.0 cm) were produced by parental lines Sarsabz and Nesser respectively.Pawar et al. [15] suggested that single spike and single plant selection could be used to supplement pedigree selection in early segregating generation.Number of spikelets spike -1 may directly contribute towards grain yield.The analysis of variance showed significant difference among heritability values as shown in (Table 1).Generally spikes with more number of spikelets spike -1 are supposed to produce more grains per spike, consequently produce higher yield plant -1 .The mean performance in (Table 4) showed that the maximum number of spikelets spike -1 (24.3) were produced by parental line Bhittai; whereas, a comparison of mean value indicated that number of spikelets spike indicated that certain components of grain yield in wheat are more heritable than others.The grain yield is the total out-put of yield components.The mean performances of progenies were highly significant at P≤0.01.The average performance of grain yield per plant of genotypes also showed significant differences (Table 5).The maximum grains spike -1 (29.0 g) were recorded in progeny Sarsabz x FD-83 as compared to other genotypes.The minimum grain yield plant -1 (13.0g) was observed in progeny FD-83 x Bhittai.Highly significant differences were observed among wheat genotypes for biological yield in both the environments.The mean performances (Table 5) of progenies were highly significant at P≤0.01 among the progenies regarding the trait biological yield kg ha -1 .The maximum biological yield -1 kg ha -1 was showed by (22960) FD-83 x Bhittai.This progeny showed significant increase in their dry mater (biological weight) than all the parental varieties.Both the progenies are good combiner and also showed Nesser x FD-83 and Nesser x Bhittai (2074).The yield is a total of genetic expression of all the yield components and believed to be a very complex character and its manifestation is influenced by the environmental as well as physiological factors  1).Generally spikes with more number of spikelets spike -1 are supposed to produce more grains spike -1 , consequently produce higher yield plant -1 .High heritability in wheat has been observed by various researchers for spikelet spike -1 [34,35].The mean performance showed significant difference at P≤0.01 among the progenies regarding the trait grains spike -1 , and it is represented in (Table 7).Similarly, the cross that showed maximum heritability percentage was FD-83 x Bhittai (85.05 %) showed highest heritability (h 2 ) percentage coupled with more genetic advanced (G.A 5.39 respectively).Our results are similar to those reported by Mothatasham et al., (2009) and Sial et al. (2007).Hassan, (2003) [36-38] the parameters grains spike -1 has direct influence on yield while, more the number of grains will get more grains yield.The results of average performance for character grains spike -1 is represented in (Table 7).The maximum grains spike -1 that the progeny Nesser x Bhittai (94.32 %) reflected highest heritability (h 2 ) associated with the highest genetic advance (42.83) followed by Nesser x FD-83 respectively.A fairly high heritability and genetic advance of all the combinations for grains spike -1 indicated that progenies of these crosses would be useful for improving grains spike -1 .The analysis of variance showed significant difference at P≤0.01 among genotypes regarding the trait grains spike -1 , and is represented in (Table 1).High heritability associated with high genetic advance for different yield components have a better scope for selecting high yielding genotypes [25].The heritability and genetic advance regarding the traits seed index 1000-grain weight (g) are shown in (Table 7).Similarly, the cross that showed maximum heritability percentage was Sarsabz x FD-83 (89.83 %), coupled with highest genetic advance (G.A 42.90 % respectively).While the five minimum progenies Nesser x FD-83, FD-83 x Bhittai, Nesser x Sarsabz, Sarsabz x Bhittai & Nesser x Bhittai showed positive value regarding this character.Hence, such genotypes should be utilized for further studies on heritability estimates as they may provides which more 1000-grain weight, consequently more yield in wheat.Grain yield is governed by such matric traits and the correlation between different parameters.Several research studies have been carried out on relationship of various yield components and also climatic factors with grain yield and its related traits [11].It is observed from (Table 8), the maximum heritability percentage was Nesser x FD-83 (77.39 %), associated with more genetic advance (18.22 respectively).Heritability estimates reported by Rehman and Kronstad [26] indicate that certain components of grain yield in wheat are more heritable than others.The heritability and genetic advance regarding the traits biological yield kg ha -1 are presented in (Table 8).All the progenies showed positive heritability percentage (h 2 ) in broad sense, for the trait biological yield maximum yield per plant was exhibited by FD-83 x Bhittai (99.96 kg ha -1 ), whereas; minimum yield was produced by Nesser x Sarsabz (99.9 kg ha -1 ) coupled with more genetic advance (G.A 11898.7 and 9425.6 kg ha -1 respectively).Genetic parameters for yield traits in wheat under 976 biological yields were comparatively greater under rainfed environment.

Conclusion
It is concluded that four progenies Sarsabaz x Bhittai, FD-83 x Bhittai, Sarsabaz x FD-83, Nesser x FD-83 and Nesser x Bhittai showed better performance for maximum days to maturity as compared to their respective parental lines.

6 .
[11].The experiment was laid out in randomized complete block design with three replications arranged in a plot size 0.45 m 2 /single spike progeny row (1.35 m 2 /3 single spike progeny row) each 1.5 meter long.There were ten genotypes under study; Nesser x FD-83 The agronomical parameters were observed Number of tillers plant -1 , maturity, Spike length (cm), Number of spikelet spike -1 , Number of grains spike -1 , 1000-grains weight (g), Grain yield plant -1 (g) and Biological yield kg ha -1 .

Table 1 . Analysis of variance showing mean squares for various morphological traits of six F4 generations and 4 parental varieties of wheat Source of variation Mean square of various traits
).

Table 3 . Comparison of mean performance of various traits of six F4 populations and their 4 parental lines of wheat for various traits Cross combination Parents/ cross Days to 75% Maturity Tillers plant -1 Spike Length (cm) Spikelets Spike -1 Grains Spike -1 1000 Grain Weight (g) Grain Yield plant -1 (g) Biological yield (Kg ha -1 )
Minimum days to maturity were taken by parental varieties Sarsabz, Bhittai, FD-83 and two progenies viz., Nesser x FD-83, Nesser x Bhittai (114.3, 114.7, 115.3, 114.7 and 116.7 days respectively); however the difference among genotypes was nonsignificant.