Heterosis and Inbreeding Depression in F 2 Populations of Upland Cotton ( Gossypium hirsutum L . )

Hybrid cotton production through exploitation of heterosis is the only way for having vertical improvement and betterment in seed cotton yield which has been stagnated in the recent years. The current study was conducted to evaluate the performance of F2 population for studying mean performance, heterotic effects and inbreeding depression in upland cotton for polygenic traits. Parental genotypes and their F2s were sown at Khyber Pakhtunkhwa Agricultural University, Peshawar during 2010, manually. All the traits revealed highly significant (p ≤ 0.01) variations for both parents and their F2 hybrids. Mean performance for parents and their F2 hybrids is: (5.26 to 7.12 & 4.43 to 6.60) seeds locule, (21.10 to 28.03 & 20.40 to 28.50) seed boll, (32.20 to 34.80 & 32.22 to 35.05) lint% and (62.87 to 85.47 & 45.94 to 92.04) seed cotton yield plant, respectively. Heterotic effects found over mid parent and better parent were: 66.66% & 46.66% (seeds locule), 60% & 30% (seed boll), 43.33% & 30% (lint %) and 36.66% & 16.66% (seed cotton yield plant), respectively. For the parameters: seeds locule (11 & 10), seeds boll (2 & 1) and seed cotton yield plant (3 & 1) showed positive highly significant heterosis for both mid and better parent, respectively while lint% did not reveal any positive significant heterosis. F2 populations i.e. CIM-499 × CIM-554 and CIM-554 × CIM-499 revealed highly significant heterotic effects over mid and better parent for all the traits except lint % while CIM-554 × CIM-707 showed highly significant heterotic effects for seeds locule and seed cotton yield palnt. Positive economic heterotic effects were also exhibited by more than 50% of the F2 population i.e., 76.66% for seed locule, 50% for seeds boll, 3.33% for lint% and 20% for seed cotton yield plant, respectively. By comparing F2 mean values with F1s, only lint % showed (0.00% to 15.55%) maxiHow to cite this paper: Khan, B.A., Khan, N.U., Ahmed, M., Iqbal, M., Ullah, I., Saleem, M., Khurshid, I. and Kanwal, A. (2017) Heterosis and Inbreeding Depression in F2 Populations of Upland Cotton (Gossypium hirsutum L.). Agricultural Sciences, 8, 1283-1295. https://doi.org/10.4236/as.2017.811093 Received: November 28, 2016 Accepted: November 14, 2017 Published: November 17, 2017 Copyright © 2017 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
Cotton (Gossypium hirsutum L.) is a major cash crop, often cross-pollinated, long day plant belonging to the family Malvacae.It is a sixth largest source of vegetable oil in the world and can boost up the economy of any country by producing edible oil for human consumption, feed (seed cake) for animals and local consumption in textile industries.Worldwide, most common cultivated species of cotton is Gossypium hirsutum L., a tetraploid, also called as upland cotton and provides 90% fiber production while Gossypium barbadense called as Egyptian cotton produces only 3% fiber.These both species are also known as new world cotton [1].
Heterosis (over better parent) is a best source for improvement of F 1 and F 2 hybrids for production.It has ability which can lead breeders for commercial utilization of valuable hybrid combinations in breeding program.It can also play a vital role for selection of potential parents with desired vigor, maternal effects and genetic variance.Hybrid cotton has successfully attracted the concentration of cotton breeders for commercial utilization of hybrid progenies [2].However, hybrid cotton has been produced successfully on primary basis since 1960s in countries like China and India due to availability of cheaper labor.
Inbreeding depression is also related to high heterosis in F 1 hybrids and has to search for moderate type of heterosis which has some stability to have less inbreeding depression at F 2 level [3].Allelic and non-allelic interactions of genes in presence of specific environmental effects will lead us to successful heterosis results.Superiority of hybrids over commercial cultivars and genotypes is known as useful heterosis [4].It is a well-known fact that without proper combination of parents, heterosis does not occur.Heterosis can be used for enhancement of cotton production by exploitation of heterozygosity and to get such cotton hybrids which are superior to best parents.The comparison of performance of the best hybrids with standard cultivars will result in determination of economic heterosis.
The F 2 lines revealed larger range of adaptation regarding to their parents and F 1 hybrids due to presence of genetic variation and larger heterogenity [5]  and even less when heterosis is defined in terms of the higher yielding parent.
Nonetheless, F 2 lines with lower inbreeding depression in yield and superior performance than well-adapted cultivars have been found.The existence of such lines lends credibility to the use of F 2 s in hybrid cotton production.Previous findings are also of view about the F 2 hybrids heterosis in cotton [7].On the other hand, a group of physical properties can play a vital role in determination of textile use and economic value of cotton.The cotton hybrid can be produced through heterobeltiosis by crossing two cotton cultivars to enhance seed production in combination with better fiber quality [8].
A successful cotton breeding program depends upon the choice and use of best parental lines for crossing and selection of favorable gene combinations.
Improvements in cotton yields can be made by applying dependable tools to cotton breeders regarding to heterotic studies and inbreeding depression.For enhancement of production per unit area by proper availability of environment, identification and selection of genotypes with best genetic potential is a regular requirement.In view of economic importance of hybrid cotton cultivation and importance of selected hybrids in segregating generations, the current research was undertaken to study the genetic potential, heterotic effects and inbreeding depression for yield related traits in 6 × 6 F 2 diallel populations of upland cotton.and inbreeding depression in parental genotypes and their F 2 populations of upland cotton for polygenic traits were conducted at Khyber Pakhtunkhwa Agricultural University, Peshawar during 2010.The hand sown method was used for parental genotypes and their F 2 s in a randomized complete block (RCB) design with three replications.Each treatment was consisted of two rows having four meter length with 30 cm plant to plant and 75 cm row to row distance.All the recommended cultural practices and inputs were applied for all the entries from time of sowing till the harvesting including fertilizer, hoeing, irrigation and pest control and the crop was grown in uniform conditions to reduce the environmental variability.Boll picking was done for two times on single plant basis and ginning was made with eight saw-gins.

Materials and Methods
Statistical analysis: Data for all the variables were analyzed through analysis of variance (ANOVA) [9].After getting the significant differences, the means were further compared and separated with least significant difference (LSD) test.
Heterosis: The F 2 heterosis over mid parents was calculated in terms of percent increase (+) or decrease (−) of F 2 hybrids against its mid parent values according to the following formula [10].
The F 2 heterobeltiosis (heterosis over better parents) was formulated in terms of percent increase/decrease of F 2 hybrid over its better parent according to [11] by using following formula.

2
Heterobeltiosis % 100 The "t" test was used to determine whether the mid and better parents F 2 heterosis was significant or not.The "t" values were computed by using the following formula according to [12].
( ) where; For assessment of economic heterosis, the cultivar CIM-473 was used as check cultivar and was also grown with other cultivars but was not included in 6 × 6 diallel hybrids.The check cultivar was compared with mean values of other parental cultivars and F 2 hybrids and economic heterosis was formulated.
Inbreeding depression: Inbreeding depression in F 2 hybrids was calculated as percent decrease of F 2 hybrids when compared with F 1 hybrid means as outlined

Results and Discussion
Regarding analysis of variance, the mean values for thirty six cotton genotypes including six parents and their 30 F 2 hybrids revealed highly significant differences (p ≤ 0.01) for seeds per locule, seeds per bolls, lint % and seed cotton yield per plant, respectively (Table 1).  to enhance the seed cotton yield at end.Highest negative inbreeding depression was noted in CIM-506 × CIM-496 while lowest negative inbreeding depression was observed in CIM-707 × CIM-506 having values −41.86% and −3.64%, respectively (Table 3).It has also been suggested that little inbreeding depression exists for F 2 and F 3 generations and it is possible to screen and select high yielding F 2 hybrids [18].Indication of high inbreeding depression even by having superior heterotic performances was also revealed that high performing hybrids had showed high inbreeding depression.It has elaborated that F 2 populations can be used as hybrid cotton if have better performance over their superior parents because F 2 crop can easily be managed with increased amount of seed produced by F 1 plants [19].Therefore, in cotton the F 2 populations could be used for hybrid cotton production.(CIM-506 × CIM-707).Overall, 60%, 30% and 50% of mid parent, better parent and economic heterosis has been recorded for the said trait (Table 3).It was suggested that little inbreeding depression exists for F 2 and F 3 generations and it is possible to screen and select high yielding F 2 hybrids as already mentioned above.In case of inbreeding depression, only one F 2 hybrid (CIM-506 × CIM-707) performed positively and showed (2.41%) positive inbreeding depression while rest of F 2 population performed well by showing stability even after segregation and revealed negative inbreeding depression ranged from −5.71% (CIM-499 × CIM-446) to −37.15% (CIM-506 × CIM-554) (Table 3).It was also showed that high performing hybrids showed high inbreeding depression.High inbreeding depression was performed by high performing hybrids.The existence of superior lines in F 2 reveals that superior alleles for the trait may have accumulated in the same line.The seeds per ball is a quantitative trait so additive gene action may be involved and those have contributed in the better performance.Results supported the idea that F 2 populations could work as a hybrid crop if properly managed and if parents selected on basis of F 2 performance, be- respectively and revealed positive inbreeding depression for the said trait (Table 4).Lower magnitude of inbreeding depression for lint % and staple length indicated that additive genes were responsible for the expression of these traits [25].
Seed cotton yield per plant: Seed cotton yield varied from 55.

2ijF=
Mean of the ij th F cross.ij MP = Mid parent value for the ij th cross.ij BP = Better parent value for the ij th cross.EMS = Error mean square.
[6]. can produce better combinations of fiber quality and yield than their parents and F 2 s yield was highly correlated with F 1 s and parental lines.It is expected that F 2 populations express only 50% of the economic heterosis shown by F 1 hybrids, B. A.Khan et al.

Table 1 .
The traits wise results about genetic potential, heterosis over mid and better parents and inbreeding depression in F 2 populations in light of previous review are discussed as follows.Mean squares and CV% of various Morpho-yield traits of upland cotton.
[17]pulation (Table2).Seeds per locule play a vital role in determining of seed cotton yield and is highly associated with production of boll number means high boll number will lead to more number of locules and ultimately produce more seed cotton yield, before ginning.Out of 30 F 2 cross combinations, 20 showed positive value of mid parents heterosis ranged from 0.00% (CIM-446 × CIM-554) to 22.22% (CIM-554 × CIM-707), while 14 F 2 hybrids revealed superior performances over their parents ranged from 0.17% (CIM-496 × CIM-707) to 19.13% (CIM-554 × CIM-707).Remaining, F 2 population showed negative heterotic performance for mid parent and better parent.Collectively, 22 F 2 hybrids showed significant heterosis for mid parent and better parent, respectively[14][15] [16][17].Moreover, 23 F 2 hybrids revealed 76.66% economic heterosis ranged from 1.99% (CIM-554 × CIM-506) to 19.13% (CIM-554 × CIM-707).It is expected that F 2 populations express 50% of the economic heterosis shown by F 1 hybrids, and even less when heterosis is defined in terms of the higher yielding parent.Overall, 66.66%, 46.66% and 76.66% heterotic performance was recorded for mid parent, better parent and for economic heterosis, respectively (Table3).In case of inbreeding depression, F 2 population performed better and showed negative inbreeding depression except the cross CIM-554 × CIM-499 which only performed (0.00%) positively means F 2 population have increased the number of seeds per locule which is desirable **, Significant at p ≤ 0.01.

Table 2 .
Mean performance of parental cultivars and F 2 s for Morpho-yield traits of upland cotton.

Table 4 .
Heterosis (MP, BP & Eco.) and Inbreeding Depression for lint% and Seed cotton yield plant −1 in F 2 s of upland cotton.