1. Introduction

Cotton is a crucial cash crop for millions of farmers worldwide in many developing economies. In Egypt, cotton is an important source of textile manufacturing. Egyptian cotton has prevailed as one of Egypt's biggest competitive advantages. With an established reputation of being the best cotton in the world, its fineness, strength and superior characteristics, have positioned Egyptian cotton products as the world's finest. Pedigree selection method has become the most common plant breeding procedure. Most of Egyptian cotton varieties were produced by this method. Both of pedigree selection and independent culling levels (ICL) were used in maintenance and renewing Egyptian cotton varieties. Selection index techniques can be used to improve several traits simultaneously ^{[1, 2, 3, 4]}. Computers provide a good opportunity to use such techniques in plant breeding programs. Selection depends mainly upon genetic variability ^{[2, 5, 6]}. Similarly, high degrees of heritability for plant height, bolls/plant and seed cotton yield/plant ranged from 72.97 to 75.55% has been recorded ^[9]. Whereas, El-Lawendy and El-Dhan ^[10] found that heritability obtained in both F3 and F4 generations ranged from moderate to high (51.3 to 96.3%) for all studied traits. After two cycles of selection for lint percentage in two segregating populations, broad sense heritability was estimated as 64 and 73% for two populations ^[11]. Employing selection index techniques were mostly better than single trait selection [6,7,8,10,12-21]. Maintaining of the Egyptian cotton varieties is the ability to keep the cotton variety out of the genetic changes “deterioration” so that the standard characters of such variety will be stable for a long time. And providing the cotton area for each variety annually by new waves of, genetically pure cottonseed stocks. The breeder mainly concerned on preservation of the known fiber properties of a variety rather than yield. Therefore, yield of the Egyptian cotton varieties is lower than that of Upland cottons. The main objective of this work was to evaluate the method of maintaining and renewing the breeder seeds of Giza 90 followed by Maintenance Research Section for renewing the Egyptian cotton strains and varieties, Cotton Research Institute, A.R.C., and the possibility of selection elite high yielding plants characterized by the same fiber properties of Giza 90.

2. Materials and Methods

The present study was carried out at Shandaweel Research Station, Cotton Res. Inst., Sohag (lat 26° 56' N, long, 31° 69' E), during the three summer seasons of 2013 -2015. The basic materials were selfed seeds of 60 single plants selected from the breeding nursery of renewal and maintenance of Giza 90 (the same materials for producing the nucleolus of G.90). Giza 90 is traced back to a cross between Giza 83 x Dandara, and released commercially in year 2000. G.90 is a commercial Egyptian cotton cultivar (G. barabadense L.) cultivated at upper and middle Egypt regions and characterized by high yielding ability, high ginning outturn (more than 120 pounds), and early maturity with staple length of about 31 mm. These materials were subjected to three methods of pedigree selection; single trait selection for lint yield/plant, selection index method, the traditional method followed by Cotton Maintenance Res. Sec. for renewing and maintenance of Egyptian cotton varieties. This method was represented by check strain (the newest nucleolus of Giza 90) in the experiment each year. In season 2013, selfed seeds of the 60 selected plants were planted on March 28, 2013, each in a plot in the breeding nursery. Each plot included five rows (10 plants in rows) 7.0 m long, 60 cm apart and 70 cm between hills within a row. The middle row was left without planting to facilitate plant screening and selfing. The total number of selfed plants were 847. At flowering, days to first flower (DFF) was recorded flower for each plant. Before picking 10 open sound bolls were picked from each plant to measure; average boll weight (BW), seed index (SI; 100-seed weight) and lint index; (LI), estimated as "weight of lint in a sample/ weight of seeds in this sample * seed index". After picking at the end of the season the following characters were recorded for each single plant; seed cotton yield /plant (SCY/P), lint yield /plant (LY/P), lint percentage (lint%) [lint yield/seed cotton yield], number of bolls/plant (NB/P), number of seeds/boll (NS/B) [boll weight x (100-lint%) /seed index], Micronaire reading (MIC), fiber strength as Pressley index measured by the H.V.I instrument (PI) and Upper half mean length; mm as measured by the H.V.I. instrument (UHM).

Two selection approaches were implemented; i) single trait selection where selfed seeds of the best 20 single plants in LY/P were selected for the growing season 2014, and ii) selection index approach where the selected single plants (847) were ranked using 13 models of the modified "desired genetic gain" ^{[3, 4]}. Selfed seeds of the 20 superior plants for each model were selected for next season.

In season 2014, the selected plants of the 14 selection procedures were planted on April 1 ^st, 2014. The selfed seeds of each selected plant were used in planting. A randomized complete blocks design of three replications was used. The plot was single row 4 m in length, 60 cm apart and 50 cm between hills within a row. One row was left without planting between each two rows to facilitate selfing and screening. After full emergence the hills were thinned to one plants/hills. The recommended cultural practices for cotton production were adopted thought the growing season. The studied characters were recorded as in the previous season. The selfed seeds of the best 10 plants for each procedure were saved for evaluation in the next season. In Season 2015, selfed seeds of a total of 67 selected plants from season 2014 covered all selection procedures a long with G.90 nucleolus (this nucleolus was produced from the same basic materials) were planted on March 25, 2015 in a randomized complete blocks design of three replications as in the previous season. The studied characters were recorded as in the previous season.

Phenotypic covariance between pairs of traits of single plants in 2013 season was estimated based on the mathematical fact:

Estimatates of genotypic variances and covariances in the second and third seasons were calculated from EMS and EMCP components of the selected familis as outlined by Walker ^[12]. Calculation of selection indices was done according to Pesek and Baker ^{[3, 4]}. The desired genetic gain was assigned as 10% increase from the population mean of each trait in the index. The phenotypic value of a family (I) was estimated using the following formula as outlined by Smith ^[1] and Hazel ^[22]. Heritability was estimated as: (H) = (σ²_g / σ²_p) x 100. The phenotypic and genotypic coefficients of variation were estimated using the formula developed by Burton ^[23]. Mean comparisons were calculated by using revised according to El Rawi and Khalafalla ^[24]. The significance of observed direct and correlated response to selection was measured as deviation percentage of family mean from the check strain using L.S.D.

To compare the different applied selection procedures, the procedures were subjected to two criteria; i) the number of families showed significant observed genetic gain in LY/P and the total sum of their genetic gains, and ii) The number of families showed significant observed genetic gain in LY/P > 25% of the check strain and the total sum of their genetic gains.

3. Results

Seed cotton yield /plant, lint yield/plant and number of bolls /plant showed wide range of variation accompanied with high coefficients of variation of 39.70, 39.52 and 39.45% for SCY/P, LY/P and NB/P, respectively (Table 1). The coefficient of variability was medium for boll weight and number of seeds/boll and accounted for 8.40 and 8.75%, respectively. Otherwise, the coefficients of variability in seed index, lint index, days to first flower and technological properties were very low and ranged from 2.49 for days to first flower to 7.40% for Micronaire reading.

Table 1. Average, maximum, minimum and coefficient of variation of the studied traits of the base population and the adopted selection procedures; season 2013

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Analysis of variance of the studied traits of the selected families after the second cycle selection is shown in Table 2. Analysis of variances of different traits was performed two times. The first was for the selected families to estimate GCV%, PCV%, and heritability of the traits under selection pressure. The second was for the selected families a long with check strain (the newest nucleolus Giza 90) to compare different selected families with check strain. Analysis of variance showed that the genotypes mean squares (families) were not significant for LY/P, SCY/P and NB/P when selection practiced for LY/P. However, mean squares of genotypes of the other traits were significant, suggesting the absence of genetic variability in LY/P for further cycle of selection. Therefore, two cycles of single trait selection for lint yield/ plant depleted greatly the coefficient of variability and was enough to isolate the elite families. However, selection indices which included LY/ P showed GCV% larger than that of selection for LY/ P per se. The genetic coefficient of variation in LY/ P was 10.35, 9.75, 5.65, 12.35, 12.32, 5.33, 7.61 and 0.0 for indices No.1, No.2, No.3, No.4, No.5, No.11, No.12 and No.13, respectively. It could be concluded that the genetic variability after selection indices in general was larger than that after single trait selection. Heritability estimate for LY /P ranged from 61.87% for index 4 to 90.78% for index 1.

Table 2. Mean squares, genotypic (GCV %) and phenotypic (PCV%) coefficients of variation and broad sense heritability estimates (H) of the studied traits of the adopted selection procedures; season 2015 (ANOVA without check)

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Mean values of the ten selected families and their observed genetic gain after two cycles of selection for different selection procedures are shown in Table 3. Mean observed genetic gain in LY/P ranged from insignificant (16.57%) for index 2 (LY/P and BW) to 21.63% (P ≤0.01) for index 7 (NB/P and NS/B). Index 2 increased BW by 9.27% (p ≤ 0.05) and UHM length by 2.23% (p ≤ 0.01). Index 7 showed a significant genetic gain of 20.26, 21.63, 3.16, 5.44 and 2.785 for SCY/P, LY/P, SI, PI, and UHM length, respectively. Index 3 showed a significant genetic gain of 19.71, 21.36, 3.61, 7.82, and 2.65% for SCY/P, LY/P, SI, PI and UHM length, respectively. Index 13 yielded a significant genetic gain 18.46, 20.55 and 5.76% for SCY/P, LY/P and PI, respectively. Single trait selection for LY/P showed a significant genetic gain of 19.75, 20.30 and 14.01% for SCY/P, LY/P and NB/P, respectively. It is of interest to indicate that the overall mean of the selected families masked the superior selected families for each selection procedures. In autogamous crops the breeder in the late generation seeks individual superior families. Therefore, the individual superior families will be presented in Table 5.

Table 3. Mean of the ten selected families and their observed genetic gain in percentage of the check strain after two cycles of selection; season 2015

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Table 5 revealed that many models of selection index were superior to single trait selection for LY/P. Furthermore; the results indicate the possibility of isolate high yielding families out yielded Giza 90 with remarkable favorable increase in one or more of the three main fiber properties, e.g., Indices 1, 2 and 12 succeeded to isolate four high yielding families with remarkable increase in UHM length. The four families were family No. 803, No. 806, No. 585 and No. 630. Significant (P≤ 0.01) genetic gain in LY/P ranged from 22.58 (family No. 630) to 38.84 % (family No. 585). Furthermore, significant genetic gain in length was achieved of 6.51% (32.17mm), 8.28% (32.70mm), 6.73% (32.23mm) and 6.95% (32.20mm) for the four respective families. It is a great opportunity to isolate new strain from Giza 90 (30.2mm) out yielded it and improved G90 to higher category in fiber length. Family No .766, No. 706 and No. 334 are promising strain out yielded (P≤ 0.01) Giza 90 and characterized by fine fibers (low Micronaire reading). Family No. 766 recorded genetic gain (P≤ 0.01) of 12.32, -15.38 (3.3) and 10.84% for LY/P, Micronaire reading and PI, respectively. Family No. 766 is a promising high yielding and converts Giza 90 from coarse (3.9 Mic) to more fine 3.3 Mic and strongest fiber. Families No. 437, No. 586, No. 803 and No. 529 are another great opportunity to increase yield of Giza and increase fiber strength by 14.39 to 16.11%. Table 5 shows 15 promising elite strains characterized by high yielding ability with improve in one or more of the three main fiber properties.

Selection procedures were subjected to two ranks. The first was for the number of detected families showed significant genetic gain in LY/P. The second rank was for the number of detected families showed significant genetic gain in LY/P ≥25% of check strain. In the first rank (Table 4) in which significant genetic gain were summed, index 1 (LY/P and NB/P) ranked the first and scored total gain of 206.97 % followed by index 3(LY/P and NS/B), selection for LY/P per se, index 9 (NB/P and SI) and selection index7 (NB/P and NS/B). In the second rank, the significant genetic gain in LY/P more than 25 % of the check strain, the genetic gain of the superior families in LY/P were summed. Selection index 7 ranked the first, index 9 ranked the second, index 1 ranked the third, index 3 ranked the fourth, and selection for LY/P per se ranked the ninth. It could be concluded that selection index was better than single trait selection in detecting the superior families in LY/P.

Table 4. Number of detected families showed significant observed genetic gain in LY/P and observed genetic gain ≥25 % of the check strain after two cycles of selection

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Table 5. Observed genetic gain in percentage of the check strain for lint yield and fiber properties

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4. Discussion

Egyptian cotton varieties have a world reputation for it high quality properties. Each variety has its own fiber and yarn characteristics. The importance of a cotton variety depends mainly upon its own fiber and yarn characteristics rather than its yielding ability. Therefore, Cotton Varieties Maintenance Research Section, ARC follows certain steps for many decades for renewing and maintaining and increase the breeder seeds of different Egyptian cotton varieties (materials and methods). The breeder devotes all his efforts during the steps of the maintenance program to preserve fiber and yarn qualities of the variety using independent culling levels method (ICL) during fiber tests. Therefore, the phenotypic coefficient of variation of the basic materials of this work was high as 39.70, 39.52 and 39.45 % for SCY/P, LY/P, and NB/P, respectively compared to quality traits (2.49, 7.40, 4.83 and 5.70 % for DFF, Micronaire reading, pressley index and UHM length, respectively), while it was dropped to an estimate of zero after two cycles of selection. These results confirm the concept that long times of artificial selfing of Giza 90 plants in the breeding nursery for more than 16 year ago (Giza 90 released in year 2000) resulted in a mixture of homozygous families similar to great extent in fiber properties and differ in yielding ability, and selection become “pure line selection”, and two cycles of selection for LY/ P was sufficient to isolate the elite families. Numerous studies have been published in agreement with our results, e.g., Srour et al. ^[25] reported a decrease in PCV and GCV% from F2 to F3, however heritability was increased. Variability in LY/P, earliness index, SCY/ P, BW and NB/S was decreased after two cycles of selection in segregating populations ^{[26, 27, 28, 29]}. Similarly, a remarkable decrease in genetic variability and high estimates heritability was found after two cycles of selection for earliness index, LY/ P and NB/ P ^{[11, 30, 31]}.

The main goal of this work was to isolate and detect elite high yielding families matched Giza 90 type in terms of fiber properties and /or high yielding families improved for one or more of three main fiber properties; fineness, strength and length. The basic materials of Giza 90 in year 2013 in the breeding nursery were subject to single trait selection for LY/P and 13 selection indices involved two or three characters for two cycles of selection. It is difficult to compare the efficiency of all these procedures, because a procedure could improve a character and affect adversely the others. The question should be answered was how to measure the efficiency if two or more procedures of selection detected the same number of families which showed significant genetic gain in LY/P? To answer this question, the observed genetic gain of the detected families was summed to give total genetic gain. Several studies indicated that selection index techniques were mostly better than single trait selection [6,7,8,10,12-21].

Our data reflect the method of renewing strains and varieties of Egyptian cotton. The breeder devotes his effort to insure technological properties; fineness, strength and fiber length, and selects the plants matched Giza 90 type in fiber properties irrespective of their yield and its components. Therefore, the coefficients of variability of Micronaire reading, Pressely index and upper half– mean length were low, reflecting the great similarity of the plants in fiber properties. Likewise, the coefficients variability in seed index, lint index and days to first flower were low as in all Egyptian cottons. The high coefficients of variability of seed cotton yield/ plant, lint yield/ plant, number of bolls/ plant and boll weight indicates the feasibility of selection for these traits with good preservation of fiber properties. The results of PCV in the base population are in general in agreement with those reported by Mahdy et al. [26-31]^[26] and Hassaballa et al. ^[11].

In conclusion, our results revealed that the present program for maintenance and renewing Egyptian cotton varieties is a precise and perfect program to preserve fiber quality, but, not suitable for improving yielding ability. Consequently, this program should be modified to allow the isolation of superior high yielding off types from the breeding nursery characterized by improvement in one or more fiber quality.

References

[1]	Smith, H.F. (1936) A discriminant function for plant selection. Ann. Eugen., 7:240-250.
	In article		View Article
[2]	Manning, H.L. (1956) Yield improvement from a selection index technique with cotton. Heredity, 10:303-322.
	In article		View Article
[3]	Pesek, J., R.J. Baker (1969) Desired improvement in relation to selection indices. Can. J. Plant Sci., 49:803-804.
	In article		View Article
[4]	Pesek, J., R.J. Baker (1970) An application of index selection to the improvement of self-pollinated species. Can. J. Plant Sci., 50:267-276.
	In article		View Article
[5]	El-Kilany, M.A. (1976) Comparative studies of selection techniques in maintaining Egyptian cotton. Ph.D. Thesis, Cairo Univ., Egypt.
	In article
[6]	Abo El-Zahab, A.A., M.A. El-Kilany (1979) Correlated response to several selection procedures for increased lint yield in segregating generations of Egyptian cotton (Gossypium barbadense L). Beitrage trop. Landwirtsch. Veterinarmed. 17. Jg. 165-172.
	In article
[7]	Mahdy, E.E. (1983) Selection index in cotton (G. barbadense L.). Assiut J. of Agric. Sci., 14:267-282.
	In article
[8]	Mahdy, E.E. (1983) Relative effectiveness of pedigree line and recurrent selection for improving lint yield in cotton (G. barbadense L.). Assiut J. of Agric. Sci., 14:315-325.
	In article
[9]	Soomro, Z.A., M.B. Kumbhar, A.S. Larik, M. Imran, S.A. Brohi (2010) Heritability and selection response in segregating generations of Upland cotton. Pakistan J. Agric. Res., 23:25-30.
	In article
[10]	El-Lawendey, M.M., M.A.A. El-Dahan (2012) Comparison between direindirect selection and two indices in segregating population of cotton (Gossypium barbadense L.). J. Agric. Res. Kafer El-Sheikh Univ., 38(1):37-53.
	In article
[11]	Hassaballa, E.A., E.E. Mahdy, A.A. Mohamed, A.M. Aly (2012) Selection for earliness index in two segregating populations of Egyptian cotton (G. barbadense L.) under late planting. Assiut J. of Agric. Sci., 43:1-17.
	In article
[12]	Walker, J.T. (1960) The use of a selection index technique in the analysis of progeny row data. Emp. Cott. Gr. Rev., 37:81-107.
	In article
[13]	Kamalanathan, S. (1967) A selection index for lint yield in cotton (G. arboreum L.). Madras agric. J., 54: 612-618 (C.F. Plant Breed. Abst. 38: 4817, 1968).
	In article
[14]	Mahdy, E.E., E.A. Hassaballa, M.A. Khalifa, F.G. Younis (1987) Relative efficiency of three selection procedures in improving yield and its components in Egyptian cotton. Assiut J. of Agric. Sci. 18:159-175.
	In article
[15]	Singh, B., G.S. Chahal, T.H. Singh (1995) Efficiency of different selection criteria for the improvement of seed cotton yield in early segregating generations of (Gossypium hirsutum L.). Crop Improv. 22:61-64.
	In article
[16]	Gomaa, M.A.M., A.M.A. Shaheen, S.A.M. Khattab (1999) Gene action and selection indices in two cotton (Gossypium barbadense L.) crosses. Ann. Agric. Sci. Cairo, 44:293-308.
	In article
[17]	Esmail, R.M. (2007). Early generation testing for vegetative and yield characters in thirty Egyptian cotton populations. Cairo, Egypt, Bulletin of the National Research Centre (Cairo) 32(4):445-457.
	In article
[18]	EL-Okkiah A.F.H., M.M. Kassem, G.A. Sary, M.M. EL-Lawendey (2008) Improving lint yield and its components in early segregating generations of Giza 45 x Giza 75 cotton cross. Egypt. J. Agric. Res., 86:631-641.
	In article
[19]	Tang, F.Y., C. Jin, H.W. Xin, M.W. Cheng, X.W. Jun (2009) Genetic variation and selection indices of quantitative traits in Upland cotton (G. hirsutum L.) lines with high fiber quality. China Cotton Sci., 21:361-365.
	In article
[20]	Kassem, M.M., G.A. Sary, A.F.H. EL-Okkiah, M.M. EL-Lawendey (2008) Comparison of the efficiencies of the different selection procedures in three populations of Egyptian cottons (Gossypium barbadense L.). Egypt. J. Agric. Res., 86:623-629.
	In article
[21]	Mahrous, H. (2008) Selection for earliness and lint yield in early and late plantings in some populations of Egyptian cotton. Ph.D. thesis, Assiut Univ., Egypt.
	In article
[22]	Hazel, L.N. (1943) Genetic basis for selection indices. Genetics 28:476-790.
	In article		PubMed
[23]	Burton, G.W. (1952) Quantitative inheritance in grasses. 6th Intl. Grassland Cong. Proc. 1:227-238.
	In article
[24]	El Rawi, K., A.M. Kalafalla (1980) Design and Analysis of Agricultural Experiments, El Mousel Univ., Iraq.
	In article		PubMed
[25]	Srour, M.S.M., M.A. Hager, E.I. Zaazaa, E.F.EL-Hashash (2010) Genetic analysis for some yield and fiber quality traits using F2 and F3 populations in Cotton. J. Plant Prod. Mansoura Univ. 1(12):1593-1604.
	In article
[26]	Mahdy, E.E., A.A. Mohamed, M.Z. Elhifny, and H. Mahrous (2006) Pedigree selection for earliness index in two populations of Egyptian cotton. Minia J.of Agric. Res. & Devolp. 26:485-506.
	In article
[27]	Mahdy, E.E., A.A. Mohamed, M.Z. Elhifny, H. Mahrous (2007) Selection seed cotton yield in early and late sowing dates of Egyptian cotton. Minia J.of Agric. Res. & Devolp. 27:1-22.
	In article
[28]	Mahdy, E.E.; G.M.K. Hemaida; F.M.F. Abd El-Motagally, A. Mostafa (2009) Response to selection for yield under late sowing date in two populations of Egyptian cotton. Assiut J. of Agric. Sci. 40:1-25.
	In article
[29]	Mahdy, E.E., G.M.K. Hemaida; F.M.F.Abd El-Motagally, A. Mostafa (2009) Pedigree selection for lint yield, lint percentage and earliness index in late planting in two populations of Egyptian cotton Minia J. of Agric. Res.& Develop. 29:233-258.
	In article
[30]	Mahdy, E.E., E.A. Hassaballa, A.A. Mohamed, A.M. Aly (2013) Pedigree selection for lint yield at late planting Egyptian cotton (G. barbadense L.). Assiut J. Agric. Sci. 45:1-15.
	In article
[31]	Mahdy, E.E., E.A. Hassaballa, A.A. Mohamed, A.M. Aly (2013) Pedigree selection for number of bolls/plant in two populations of Egyptian cotton under late planting conditions. J. Production and Development, Mansoura Univ. 17(2): 400-418.
	In article