Inbreeding depression analysis in F 2 segregating population of bread wheat

The present experiment was conducted to analysis mean performance and inbreeding depression in six F2 hybrids. The F2 populations of wheat along with their parents differed significantly (P≤0.01) for all yield and its components, suggesting that abundant genetic diversity is available in these genotypes. For mean performance, among the parents, the variety TD-1 demonstrated better performance for early maturity, plant height, tillers plant, spikelets spike, grains spike, seed index and grain yield plant; however, among the F2 progenies, the F2 progeny TD-1 x Imdad exhibited better performance for various traits such as days to 50% heading, plant height, grains spike, seed index and grain yield plant, indicating that these genetic resources can further be utilized in various breeding programs to improve bread wheat. With regards to inbreeding depression, the F2 progeny TJ-83 x Moomal expressed low amount of inbreeding depression for various traits including spike length (-9.88%), spikelets spike (-0.82%), seed index (-5.98%), grain yield plant (-3.62%) while same F2 progeny also showed maximum (3.72%) inbreeding depression for the trait days to 50% heading, and indeed is desirable for that trait. Consequently, the F2 progeny TJ-83 x Moomal would be useful F2 hybrid to be utilized for commercial cultivation since this progeny showed minimum inbreeding depression for variety of traits.


Introduction
Wheat is a principal crop and considered as a great source of carbohydrates in human diet.It is extensively cultivated in Pakistan and used as major staple food [1].Human population of the world is rising at a great pace; hence there is demand for stunning improvement in food production to feed increasing population.Due to considerable achievements made in crop research, quite a large number of new crop cultivars have been evolved and the production has been outstandingly improved all over the world.Wheat breeders have been done a great deal of research on wheat crop in Pakistan and as a consequences country is self-sufficient in wheat production [2].For any successful breeding program, the proper parental selection and the breeder's intense judgment in selecting promising genotypes within the segregating populations is pre-requisite.The research on heterosis and inbreeding depression in economically important crops including wheat is an essential approach for genetic parameter's interpretation.The nature and extent of heterosis and inbreeding depression may possibly play a crucial role for plant breeder in making the suitable breeding methods [3].Therefore, the current study was done to mark out the extent of inbreeding depression in bread wheat and identify superior crosses which would profitably be utilized in future wheat improvement programs.

Materials and Methods
In order to study the inbreeding depression for grain yield and its component in F2 hybrids of wheat (Triticum aestivum L.), the experiment was conducted during the year 2012-13 at the experimental field of Sindh Agriculture University, Tandojam.The seed of four parents (TD-1, TJ-83, Imdad and Moomal) along with their six F2 hybrids (TD-1 × TJ-83, TD-1 × Imdad, TD-1 × Moomal, TJ-83 × Imdad, TJ-83 × Moomal and Imdad × Moomal) of wheat were sown in Randomized Complete Block Design (RCBD) with three replications during Rabi, 2012-13.The six rows of three meter long of each genotype were grown by keeping 15 cm plant to plant and 30 cm row to row distance through hand drill method.After 25 days of germination, thinning was done to maintain plant to plant and row to row distance and all recommended agronomic practices were applied.Ten plants per replication per genotype were randomly selected and tagged for recording the various phenotypic traits (Table -2).The analysis of variance was carried out according to statistical method developed by [4], whereas inbreeding depression was calculated as suggested by [5].Inbreeding depression = F2 -F1 x 100 F1

Analysis of variance
The analysis of variance calculations (Table 1) from F2 populations of wheat along with their parents were significantly different at P<0.01 level for all the investigated traits which indicated that significance in the difference was found among the F2 hybrids as well as among the parents.This demonstrates that used plant sources may be evaluated for further research.The results of each character are discussed below.and Singh [8] and they penned inbreeding depression for all the studied traits, suggested that inbreeding depression was primarily associated with epistasis, linkage disequilibrium and abnormal segregation at meiosis due to higher ploidy level.

Tillers plant -1
Among yield components, tillers plant -1 is a vital plant attributes that enhances grain yield in wheat.To develop promising cultivars, not only grain yield but yield associated components such as tillers plant -1 also entail a special consideration.Among the parents, the maximum number of tillers plant -1 (Table -2) was produced by the genotype TD-1 (7.66), followed by TJ-83 (5.88), while among the F2 hybrids, Imdad x Moomal (7.67) resulted in maximum number of tillers plant -1 , signifying that these plant materials including parents and F2 progenies could be proved backup materials in upcoming breeding programs because these plant resources possess better yield related trait in shape of maximum tillers plant -1 as compared to other parents and crosses.The minimum inbreeding depression (Table-4) was calculated from the cross Imdad x Moomal (-0.39%), it reveals that this cross combination can further be used as hybrid since it possesses better gene recombination as compared to other F2 progenies.Similar results have also been reported by Singh [9] and Singh [10] who also found inbreeding depression for yield components in wheat including the number of tillers plant -1 .

Spikelets spike -1
Spikelets spike -1 is also an important trait in wheat, as more number of the spikelets spike -1 , more number of the grains spike -1 , consequently higher the grain yield plant -1 .
The mean performance (Table -2) referred that among the parents, the maximum number of spikelets spike -1 was counted from parent TD-1 (19.67).However in F2 hybrids, TJ-83 x Moomal gave the highest number of spikelets spike -1 (20.40), demonstrating that above mentioned parent and F2 hybrid possess greater potential to show better performance, thus could be proved useful plant materials for plant breeders.The information of inbreeding depression regarding number of spikelets spike -1 is given in Table-5.The maximum inbreeding depression was recorded in TD-1 x Moomal (-32.52%),followed by TD-1 x Imdad (-18.79%),TD-1 x TJ-83 (-17.80%) and TJ-83 x Imdad (-17.01%).However, the minimum inbreeding depression was shown by the cross of TJ-83 x Moomal (-0.82%).
Considering the low amount of inbreeding depression, various researchers [10, 11, 12] have suggested that in some cases low inbreeding depression designates additive x additive and additive x dominance type of gene action which may be a cause of low inbreeding depression.

Grains spike -1
Grains spike -1 is also a key trait in wheat breeding; it directly involves in enhancing the grain yield plant -1 .The mean performance of number of grains spike -1 (Table -2) revealed that parent TD-1 set more number of grains spike -1 (62.33) followed by Imdad (56.32).In case of F2 hybrids, TD-1 x TJ-83 set maximum number of grains spike -1 (60.53) followed by hybrid TD-1 x Imdad (57.27).In brief, these parents and F2 retain potentiality to show superior performance for future breeding programs, especially for grains spike -1 .The calculated inbreeding depression for the trait number of grains spike -1 is presented in Table-5.All F2 progenies expressed inbreeding depression, however, the observed inbreeding depression for this trait was not as greater as other traits showed in the present study, it ranged from -0.31 to -6.47%.The obtained results support the initiative that F2 populations may possibly work as a hybrid crop if suitably managed and if parents are recognized through their performance in segregating population, since F1 hybrids cannot illuminate the constancy of F2 populations.Therefore, such F2 populations would be desirable to use as hybrid wheat to enhance the grains spike -1 and eventually grain yield plant -1 .

Seed index
Seed index is one of the most important yield contributing traits.The mean performance of parents and F2 hybrids (Table -2) showed that among the parents, the cultivar TD-1 (50.10 g) resulted in maximum seed index value followed by Imdad (46.33 g).On the other hand, among the F2 hybrids, TD-1 x TJ-83 (49.90 g) recorded the highest seed index value, followed by TD-1 x Imdad (45.67 g).Indeed, the performance of these parents as well as F2 hybrids indicates their valuable use in upcoming breeding projects.Inbreeding depression for the trait seed index (1000 grain weight g) is presented in Table-6.It was found that inbreeding depression existed in all F2 progenies for seed index, ranging from -5.98 to -16.21%.However, inbreeding depression was low to moderate, indicating that little inbreeding depression exists for F2 generations and it is possible to select high yielding F2 populations for further use.

Grain yield plant -1
High grain yield is very critical for improvement of crop cultivars for farmer's perspective.Yield is a trait controlled by many genes and is end product of interaction between various genetic and environmental components.The chief objective of wheat breeding is to enhance wheat production by exploiting the potential of existing genetic materials available to them.The mean performance of F2 hybrids and their parents for grain yield plant -1 (Table -2) exhibited that among the parents, the parent TD-1 gave maximum grain yield plant -1 (16.45 g); however, among the crosses TD-1 x Imdad gave the highest grain yield plant -1 (16.33 g).Since, greater yield is always a prime objective of an agriculturist, so these breeding materials could be a valuable addition in any breeding programs.The information of inbreeding depression for grain yield plant -1 is given in