Inheritance studies in F 2 segregating populations of bread Wheat genotypes

This study was carried out to determine the inheritance pattern of various agronomic traits in six F2 segregating populations of spring wheat. In this context, an experiment was conducted at the experimental field of Southern Wheat Research Station, Tandojam during Rabi 2014-2015. The experiment was laid out in randomized complete block design with three replications. The experimental material was consisted of nine parents, including Khirman, Imdad-05, Noori, Soughat, Mexipak, Moomal, Marvi, Kiran-95 and Anmol-91 and their six F2 progenies. The analysis of variance of the genotypes (including nine parents and their six F2 progenies) showed that all the defined characters were differed significantly (P<0.05), offering the higher genetic variability among the genotypes which can further be exploited for various breeding programs to improve bread genotypes. On the basis of mean performance, among the parental lines, the parent Khirman exhibited outstanding performance for a range of characters (tillers plant, spike length, spikelets spike, grains spike and grain yield plant). Considering the F2 hybrids, the progeny Khirman × Imdad-05 showed promising results for tillers plant, spike length and spikelets spike, whereas Anmol × Marvi gave desirable results for grain yield plant and seed index, indicating that above mentioned genotypes may be proved reliable genetic resources. With regards to heritability percentage in broad sense, the F2 progeny Khirman x Imdad-05 expressed high heritability for almost all studied traits, with the exception of grain yield plant. This study suggests that most of the yield associated traits have been successfully transmitted. The information generated will be helpful for better understanding and selection of desirable material especially in advance generations.


Introduction
Wheat (Triticum aestivum L.) is the most vital and major consumable food cereal of the world, including Pakistan.It is a staple food in many countries, including Pakistan [1].The prime objective of wheat breeders is to evolve the wheat cultivars that show stability at genetic level, produce more grain yield and adapt well to a wide range of climatic conditions.Wheat requirement is increasing day by day due to ever increasing human population of the world.Competition among existing cultivars and advance lines of wheat has also shown up.Wheat cultivars with promising yield contributing characters need to be assessed and selected for further breeding [2].Heritability estimates offer information concerning the extent to which particular crop trait, such as days to maturity, plant height, tillers plant -1 , spike length, grains spike -1 , grain weight spike -1 , 1000-grain weight and grain yield plant -1 are transferred to the following generations [3].Selection would be easier, if the heritability is higher; consequently, greater will be the response to selection [4].Heritability measures the phenotypic variance which is attributable to the genetic cause.The knowledge of heritability helps the plant breeders in anticipating the behavior of the succeeding generation and provides a major component of response to the selection for a successful breeding program [5].Therefore, the current research was conducted to evaluate F2 wheat population and assess various yield traits for available variation and to study heritability and genetic advance for the traits.This information will be helpful for improving the wheat yield through reliable selection.

Materials and methods
The present experiment was conducted at the experimental field of Southern Wheat Research Station, Tandojam during Rabi 2014-2015.The experiment was laid out in randomized complete block design with three replications.In a total, nine parental varieties lines (Khirman, Imdad-05, Mexipak, Noori, Soughat, Moomal, Marvi, Kiran-95 and Anmol-91) and six intervarietial F2 hybrids (Khirman x Imdad-05, Noori x Imdad-05, Imdad-05 x Soughat, Mexipak x Moomal, Anmol-91 x Marvi and Kiran-95 x Imdad-05) were studied.The sowing was done by dibbling, keeping 20 cm space between plants and 30 cm between rows.The experimental site is situated at latitude 25o 25' 28" N, and longitude 68o 32' 25" E and is at an elevation of about 26 m above the mean sea level.The soil type was clay loam with pH 7.5.The recommended dose of fertilizer (134N: 67 P2O5 kg/ha) was applied to the experiment.The N fertilizer was used in three splits whereas P fertilizer was applied before the cultivation.The experiment was irrigated six times during entire cropping season, such as; first irrigation was applied at crown stage, second at tillering stage, third at booting stage, fourth at flowering stage, fifth at milky stage, and sixth at dough stage.The weedicide Loughran (160 grams/acre) was used to remove weeds from the experiment.The traits studied were tillers plant -1 , spike length (cm), spikelets spike -1 , grains spike -1 , grain yield plant -1 (g) and seed index (1000grain weight, g).The entire data was statistically analyzed using analysis of variance (ANOVA) as suggested by Gomez and Gomez [6] and the means were compared by least significance difference test (LSD).The heritability of different traits was calculated as proposed by Falconer [7].

Results and discussion
The combined analysis of variance including nine parents and their six F2 populations showed that parents and segregating populations differed significantly (P≤ 0.05) for all defined traits (Table 1).The mean squares for parental lines and F2 hybrids were also significantly different for majority of the studied traits, designating a high amount of genetic variability among the genotypes.

Mean performance and heritability estimates
The mean performance of parents and their F2 progenies are reported in Table 2, while heritability and genetic advance for all the traits are summarized in Table 3 and 4. The results of each character is discussed below: Tillers plant -1 Among yield components, number of tillers plant -1 is an important attribute which increase grain yield in wheat.To evolve high yielding varieties, not only grain yield but yield related traits like number of tillers plant -1 also required a special attention.The mean performance for tillers plant -1 is presented in The wheat breeding studies have reported that spikelets spike -1 may directly contribute towards grain yield.Among the genotypes, the maximum (19.46) number of spikelets spike -1 was noticed as maximum in Khirman, while minimum (13.2) was reported in Kiran-95.In case of F2 hybrids, the maximum (18.53) spikelets spike -1 noticed in Khirman × Imdad-05 and the minimum (17.00) number of spikelets spike -1 was noticed in Imdad-05 × Soughat in F2 progeny.The heritability percentage (h 2 ) for spikelets spike -1 varied from 7.39 to 51.32% (Table 3), while genetic advance varied from 0.27 to 5.32 (

Grains spike 1
The mean performance for grains spike -1 is given in Table 2.Among the parental genotypes, maximum (60.43) grains spike -1 was found in Khirman, while minimum (42.23) grains spike -1 was recorded in Anmol-91.Among the F2 progenies, the maximum (54.43) number of grains spike -1 were set in Noori × Imdad-05, whereas minimum (48.63) were set in Kiran-95 × Imdad-05.The heritability percentage (h 2 ) for the character grains spike -1 was ranged from 8.98 to 31.95%, while genetic advance was ranged from 6.39 to 28.27 (Table 4).The higher heritability percentage (h 2 =31.95%) among the F2 progenies was recorded in Khirman × Imdad-05 coupled with high genetic advance of 28.27.Similar results were also found by Sial et al. [16].These results shows that grains spike -1 could be used in direct selection criteria for grain yield improvement.

Grain yield plant -1 (g)
High grain yield is very crucial for development of crop varieties for farmer's point of view.Yield is a kind of trait which is controlled by polygenes and is the result of interplay between many genetic and nongenetic components [17].The main objective of wheat breeding is to increase wheat production by exploiting the potential of existing genetic materials available to them.Considering the parents, the maximum (10.76 g) grain yield plant -1 was Observed in Khirman, while minimum (8.50 g) grain yield plant -1 was observed in Anmol-91 (Table -2) Among the F2 population, the maximal (14.26 g) grain yield plant -1 was achieved in Anmol-91 × Marvi, while the minimal (9.976 g) grain yield plant -1 was recorded in Kiran-95 × Imdad-05.The extent of heritability percentage (h 2 ) and genetic advance for grain yield plant -1 was ranged from 2.99 to 79.51% and 0.11 to 12.48, respectively (Table 4).High heritability for trait grain yield plant -1 was displayed by cross Anmol-91 × Marvi.The high heritability is due to low environmental variance and high genetic variance for this cross, while rest of the crosses displayed low heritability.Selection will be suitable for the improvement of grain yield.Similar results were also reported by Iftikhar et al.

Seed index (1000-grain weight, g)
In respect to seed index, among the parents, Marvi stands first with the maximum 1000grain weight of 50.73 g and Noori stands at the bottom with minimum 1000-grain weight (40.05 g).The highest 1000-grain weight (44.68 g) in F2 population was recorded in Anmol-91 × Marvi, while the cross Kiran-95 × Imdad-05 showed the lowest 1000-grain weight (36.68 g) (Table 2).The heritability percentage (h 2 ) for 1000grain weight varied from 15.77 to 51.37%, while genetic advance varied from 0.95 to 5.28, and the progeny Khirman × Imdad-05 showed high heritability (h²=51.37%)with low genetic advance (GA=4.62)among the crosses (Table 4).This suggests that effective and proper selection is possible for the improvement of this trait.