Genetic Effects of Thirteen L. Chromosome Substitution Lines in Topcrosses with Upland Cotton Cultivars: I. Yield and Yield Components

Genetic Effects of Thirteen Gossypium barbadense L. Chromosome Substitution Linesin Topcrosses with Upland Cotton Cultivars: I. Yield and Yield Components

Johnie N. Jenkins,* Jixiang Wu, Jack C. McCarty, Sukumar Saha, Osman Gutierrez, Russell Hayes,and David M. Stelly

ABSTRACTGossypium barbadense L. line 3–79 is lower in yield, has smaller

bolls and longer, finer, and stronger fibers than upland cotton G.hirsutum L. Thirteen chromosome substitution (CS-B) lines with indi-vidual 3–79 chromosomes or arms substituted into TM-1,G. hirsutum,were top crossed with five elite cultivars and additive and dominanceeffects for the yield components, lint percentage, boll weight, seedcotton yield, and lint yield, were measured over four environments.Additive effects were greater than dominance effects for all traits. CS-Blines had smaller additive and homozygous dominance effects than thecultivars for most traits. Many CS-B lines had negative additive effects;however, chromosome substituted arms 22sh and 22Lo showed additiveeffects for lint yield that were significantly greater than homologouschromosome arms in TM-1. Hybrids of DP90 3 CS-B15sh, ST 474 3

CS-B17, and FM 9663 CS-B02 had positive dominance effects for lintyield significantly greater than the homologous chromosomes in TM-1.Several chromosomes or arms were associated with significant negativeadditive or dominance effects. These data provide a valuable baselineon yield components for the utility of these CS-B lines in commercialbreeding programs. When individual chromosomes or chromosomearms, via CS-B lines, are used in crosses with cultivars, alleles for yieldcomponents on specific G. barbadense chromosomes were uncoveredthat showed positive interactions with alleles in elite germplasm.

UPLAND COTTON (Gossypium hirsutum L., 2n5 52) isthe most extensively cultivated cotton species and

has high lint productivity. It is an allelotetraploid with 13pairs of chromosomes from subgenome A and 13 fromsubgenome D. The level of intraspecific polymorphismrevealed by assessment at the DNA molecular level islow in G. hirsutum, especially among agriculturally elitetypes, (Gutierrez et al., 2002; Ulloa and Meredith, 2000;Wendel et al., 1989). Gossypium barbadense L., also acultivated species, shares the same two subgenomeswith G. hirsutum, and has superior fiber properties oflength, micronaire, and strength. Interspecific germ-plasm introgression is particularly attractive as it utilizesnatural resources and can be targeted to one or more

specific traits or genes. However, crossing these twospecies usually leads to difficulties such as infertility,cytological abnormalities and distorted segregation inthe F2 generation and beyond.

Chromosome substitution has been an indispensablemethod for intraspecific germplasm introgression intobread wheat (Triticum aestivum L., 2n 5 42) and hasbeen useful for genetic analysis and breeding (Al-Quadhy et al., 1988; Berke et al., 1992a, 1992b; Campbellet al., 2003; Campbell et al., 2004; Kaeppler, 1997; Law,1966; Mansur et al., 1990; Shah et al., 1999; Yen andBaenziger, 1992; Yen et al., 1997; Zemetra and Morris,1988, and Zemetra et al., 1986). Methods for develop-ment of interspecific chromosome substitution in G.hirsutum were outlined by Endrezzi (1963), and severalof the initially discoveredG. hirsutummonosomics wereused to substitute G. barbadense chromosomes into G.hirsutum (Endrezzi, 1963; Kohel et al., 1977; Ma andKohel, 1983). We have developed and released 17 di-somic, chromosome substitution (CS-B) lines throughhypoaneuploid-based backcross chromosome substitu-tion, using as recurrent parent a previously developedmonosomic or monotelodisomic near-isogenic backcrossderivative of TM-1. In each CS-B line, a pair of chro-mosomes (or chromosome arms) of G. hirsutum inbredTM-1 was replaced by the respective pair from G.barbadense doubled-haploid 3–79 lines (Stelly et al.,2004a, 2004b, 2005). These substitution lines are near-isogenic to the recurrent parentTM-1 for 25 chromosomepairs, and are near-isogenic to one another, for 24 chro-mosomepairs. Such a highly uniform genetic backgroundamong these CS-B lines provides an opportunity toassociate traits of importance with specific chromosomesor chromosome arms, in the TM-1 background usingcomparative analysis. In our previous research with onlydata from CS-B lines and TM-1 lines, we could not sep-arate additive and epistatic effects (Saha et al., 2004a,2004b). Study of several CS-B lines (Kohel et al., 1977;Ma and Kohel 1983) indicated that chromosome 6 wasassociated with higher lint percentage, finer fiber, andlater flowering; whereas, chromosome 17 was associatedwith short fiber length. QTL for boll size, lint percentage,fiber length, and fiber elongation were mapped tochromosome 16 using 178 families from the cross ofa substitution line for chromosome 16 and TM-1 (Renet al., 2002). Recent analyses of an expanded set of newand resynthesized CS-B lines, per se, showed that chro-mosomes 16 and 18, from 3–79, were associated withreductions in yield, and chromosome 25 of 3–79 was

Johnie N. Jenkins, Jack C. McCarty, Sukumar Saha, Osman Gutierrez,and Russell Hayes, Crop Science Research Laboratory, USDA-ARS,Mississippi State, MS 39762; Jixiang Wu, Department of Plant andSoil Sciences, Mississippi State University, Mississippi State, MS39762; David M. Stelly, Department of Soil and Crop Sciences, TexasA&M University, College Station, TX 77843-2474. Mention of tradenames or commercial products in this manuscript does not implyrecommendation or endorsement by the U. S. Department of Agri-culture. Joint Contribution of USDA-ARS and Mississippi State Uni-versity. Journal paper No. J-10780 of Mississippi Agricultural andForestry Experiment Station. Received 22 Aug. 2005. *Correspondingauthor([email protected]).

Published in Crop Sci. 46:1169–1178 (2006).Crop Breeding & Geneticsdoi:10.2135/cropsci2005.08-0269ª Crop Science Society of America677 S. Segoe Rd., Madison, WI 53711 USA

Abbreviations: CS-B, Chromosome substitution line from G. barba-dense; GCA, general combining ability; SCA, specific combiningability; RS, Recombinant substituted lines.

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associated with reduced micronaire and increased fiberlength and strength compared with TM-1 (Saha et al.,2004a, 2004b). These studies provide good geneticinformation relative to genetic association of traits withsubstituted chromosomes or chromosome arms. How-ever, the merit of these CS-B lines for breeding andgenetic improvement of upland cultivars has not beeninvestigated before this study.We crossed 13 CS-B lines, the recurrent parent TM-1,

and the donor parent 3–79 with five elite cultivars. The 75F2 hybrids and 20 parents were evaluated in four envi-ronments for yield traits. The objectives were to estimatevariance components and genetic effects to determinewhich CS-B lines can be used as good combiners forimproving cotton fiber quality and yield in breedingprograms. In addition, we can determine specific chromo-somes associated with important traits. In the presentmanuscript, we focus on yield and yield components.

MATERIALS AND METHODS

Development of Plant Materials

Five elite cultivars, Deltapine 90 (DP90); Sure-Grow 747(SG 747); Phytogen 355(PSC 355); Stoneville 474 (ST 474),and FiberMax 966(FM 966); representing the major cottonseed breeding companies in the USA, were crossed as femaleswith 13 CS-B lines (Stelly et al., 2004b, 2005), TM-1, andG. barbadense line 3–79 (Table 1). The CS-B lines includefive subgenome A and eight subgenome D chromosomes orchromosome arms from 3–79 (G. barbadense) substitutedinto TM-1.

Field Design and Procedures

The 75 top crosses were made at Mississippi State, MS, inthe summer of 2002. The F1 seeds were sent to a winter nurseryin Tecoman, Mexico, to produce the F2. The resulting 75 F2

hybrids, five cultivars, 13 CS-B lines, TM-1, and 3–79 parentswere planted at two locations in 2003 and 2004 at the PlantScience Research Center at Mississippi State, MS (33.48 N

88.89W). Soil type for Env. 1 was a Marietta loam (Fine-loamy,siliceous, active, fluvaquentic Eutrudepts) and for Env. 2, 3,and 4 was a Leeper silty clay loam (Fine, smectitic, nonacid,thermic Vertic Epiaquept). Plots were planted in a plant twoskip-one row pattern with single 9 m rows in Env. 1 and 12 mrows in Env. 2, 3, and 4, replicated 4 times in randomizedcomplete block arrangements. Rows were 0.97 m apart andplants were spaced approximately 10 cm apart within the row.Planting dates were 28 May 2003 for Env. 1 and 2 and 13 May2004 for Env. 3 and 4. Harvest dates were 3 November forEnv. 1, 31 October for Env. 2, 2 to 9 November for Env. 3, and29 October for Env. 4. Standard cultural practices were fol-lowed in each environment. A 25-boll sample was hand har-vested from first position bolls near the middle nodes of plantsin each plot. This sample was ginned on a 10-saw laboratorygin, after which, the lint and seed fractions were weighed,and lint percentage was calculated by dividing lint fraction bytotal weight of seed and lint and multiplying by 100. After theboll sample was collected, all plots were harvested with acommercial cotton picker modified to bag seed cotton fromeach plot in 2003 while in 2004 the picker was equipped withload cells for weighing seed cotton per plot.

Data Analyses

Analysis of Phenotypic Data

Yield and yield component data were analyzed by analysisof variance using SAS procedures (SAS Institute 2001). Meanswere separated by Fisher’s protected least significant differ-ence (LSD) at the 0.05 level. Parents and F2 were analyzedseparately. Mean squares for genotype effects were consider-ably greater than mean squares for the genotype 3 environ-ment interactions (data not shown), thus we report parent andF2 data as means across environments.

Genetic Analysis

An additive–dominance (AD) genetic model, with G 3 Einteraction was also used for data analysis (Tang et al., 1996;Wu et al., 1995; Zhu, 1993, 1994). This genetic model is basedon the following two genetic assumptions: (i) normal diploidsegregation and (ii) dominance effects (interaction effectsbetween alleles at each locus). The genetic model for parent iat environment h is expressed as follows,

yhiik(P) 5 m 1 Eh 1 2Ai 1 Dii 1 2AEhi 1 DEhii

1 Bk(h) 1 ehiik

The genetic model for a F2 between parents i and j atenvironment h is expressed as follows,

yhijk(F2) 5 m 1 Eh 1 (Ai 1 Aj)

1 (0:25Dii 1 0:25Djj 1 0:5Dij)

1 (AEhi 1 AEhj)

1 (0:25DEhii 1 0:25DEhjj 1 0:5DEhij)

1 Bk(h) 1 ehijk

where, m is population mean, Eh is environmental effect, Ai orAj is the additive effect, Dii, Djj, or Dij is the dominance effect,AEhi or AEhj is the additive 3 environment interaction effect,DEhii, DEhjj, or DEhij is the dominance 3 environment inter-action effect, Bk(h) is the block effect, and ehijk is the ran-dom error.

In this study, some coefficients for genetic effects werefractions rather than 0 and 1, thus, ANOVA (analysis of var-

Table 1. Mean yield and yield component values for parents.

ParentLint

percentageBoll

weightSeed cotton

yieldLintyield

% g kg ha21

DP 90 39.68 4.97 3530 1396SG 747 42.16 5.39 3512 1471PSC 355 41.16 5.04 3726 1531ST 474 43.95 5.01 3549 1541FM 966 42.10 6.04 3855 1622TM-1 34.45 5.72 2531 869CS-B02 34.68 5.70 2687 926CS-B04 34.44 5.75 2646 906CS-B06 34.46 5.72 2833 965CS-B07 34.17 5.31 2753 931CS-B16 37.69 5.69 1472 559CS-B17 30.98 5.32 2340 726CS-B18 35.32 5.32 2049 723CS-B25 32.30 5.12 2428 783CS-B05sh 35.10 5.01 2715 937CS-B14sh 32.74 4.40 2110 686CS-B15sh 32.97 5.65 2410 794CS-B22sh 37.35 5.23 2433 896CS-B22Lo 38.27 4.53 2719 10333–79 35.56 3.72 1601 567LSD 0.05 0.51 0.18 372 140

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iance) and GLM (general linear model) methods were notappropriate for the genetic analyses. The purposes of our studywere to calculate the genetic variances and genetic effects foreach genetic component. The phenotypic variance was par-titioned into components for additive (VA), dominance (VD),additive 3 environment (VAE), dominance 3 environment(VDE), and residual (Ve) and expressed as proportions ofthe total phenotypic variance (Tang et al., 1996) Thus, weconsidered m and Eh as fixed and the remaining effects asrandom. A mixed linear model approach, minimum normquadratic unbiased estimation with an initial value of 1.0 calledMINQUE1, was used to estimate the variance components(Zhu, 1998). Genetic effects were predicted by the adjustedunbiased prediction (AUP) approach (Zhu, 1993). Standarderrors of variance components and genetic effects were esti-mated by jackknife resampling over one replication withineach environment. An approximate one-tailed t test (df 5 15)was used to detect the significance of variance componentsand a two-tailed t test was used to detect the significance ofgenetic effects (Miller, 1974).

By this method, the predicted genetic effects were devia-tions from the respective population grand mean m, not fromTM-1. A t test was utilized to detect the significance of geneticeffects from zero. For the CS-B parents these are measures ofthe additive or homozygous dominance effects of the entiregenome of the CS-B parent (25 chromosomes from TM-1 andone chromosome from 3–79). In addition, a significant dif-ference for additive effects or homozygous dominance effects,for a quantitative trait, between a specific CS-B line and TM-1was considered as a significant additive or homozygous dom-inance chromosome effect because of the specific substitutedchromosome or chromosome arm from 3–79.

Among the F2 hybrids, the deviation of the heterozygousdominance effect for a CS-B line and a cultivar from the het-erozygous dominance for TM-1 line and the same cultivar canbe considered as due to the allelic interactions between thesubstituted chromosome or the chromosome arm from 3–79in the CS-B line and the homologous chromosome or arm inthe respective cultivar.

Mathematically, if we define Di1 as the heterozygous domi-nance effects between the female parent i and the male parentTM-1, and Dij as the heterozygous dominant effect betweenthe female parent i and a CS-B line j, then the value of Dij

minus Di1 can be considered as the allelic interaction effect(heterozygous dominance effect) due to the specific substi-tuted chromosome or arm from 3–79 and the homologouschromosome or arm in female cultivar parent i. This is essen-tially a probe of the specific combination between the specificchromosome in the cultivar and the homologous chromosomefrom 3–79 in the CS-B line.

The significance of the difference between the geneticseffects for a CS-B line and TM-1 was detected by the methodof Paterson (1939) using the standard error of the differencebetween two means.

RESULTS AND DISCUSSIONMean Comparisons among Parents

On the average, the five cultivar parents had higherlint percentage, seed cotton yield, and lint yield than anyCS-B line, TM-1, or 3–79 (Table 1). This was an ex-pected result because the TM-1 and 3–79 parents arefrom obsolete cultivars. ST 474 had the highest lintpercentage (43.95%) among parents. CS-B16, CS-B18,CS-B05sh, CS-B22sh, CS-B22Lo, and 3–79 had higher

lint percentage than TM-1, while CS-B17, CS-B25, CS-B14sh, and CS-B15sh had lower lint percentage thanTM-1 (Table 1). FM 966 had the heaviest bolls (6.04 g)among the parents. TM-1 bolls (5.72 g) were heavierthan four cultivars and 3–79 but were lighter than FM966. No CS-B lines produced heavier bolls than TM-1;however, CS-B07, CS-B17, CS-B18, CS-B25, CS-B05sh,CS-B14sh, CS-B22sh, CS-B22Lo, and 3–79 bolls werelighter than TM-1; whereas, CS-B02, CS-B04, CS-B06,CS-B16, and CS-B15sh were not different in boll weightthan TM-1. No CS-B lines yielded more seed cottonthan TM-1 while CS-B16, CS-B18, CS-B14sh, and 3–79yielded less seed cotton than TM-1. Among CS-B linesonly CS-B22Lo had higher lint yield than TM-1;whereas, CS-B16, CS-B17, CS-B18, and CS-B14sh hadlower lint yields than TM-1, (Table 1).

Mean Comparisons among F2 HybridsThe means of hybrids across cultivars for each CS-B

parent had higher lint percentage, heavier bolls, andgreater seedcotton and lint yields than most of the CS-Bparents, indicating that dominance effects are importantfor controlling each of these traits (Tables 1–5). Rangesamong CS-B hybrids over four environments were 35.98to 41.16% for lint percentage, 4.75 to 6.39 g for bolls,2369 to 4055 kg ha21 for seed cotton, and 895 to 1570 kgfor lint ha21 (Tables 2–5).

The mean of hybrids with FM 966 had higher lintpercentage, heavier bolls, and greater cotton yield thanthe mean of hybrids with the other four cultivars (Tables2–5). The mean of hybrids with DP 90 had lower lintpercentage (37.45%) than the mean of hybrids with eachof the other four cultivars (greater than 38%). The meanlint percentage of nine CS-B hybrids averaged acrosscultivars was greater than TM-1 hybrids across cultivars.The mean lint percentage of hybrids with CS-B22shand CS-B22Lo was greater than the mean of all otherCS-B hybrids. There were 31 individual CS-B hybridswith lint percentage significantly greater than 38%, 14

Table 2. Lint percentage of F2 hybrid from crosses of five cultivarswith CS-B lines, TM-1, and 3–79.

CultivarMaleparent† DP90 SG747 PSC355 ST474 FM966 Mean

TM-1 37.29 38.10 37.61 38.80 38.55 38.07CS-B02 37.46 38.23 37.92 38.94 38.83 38.28CS-B04 37.31 39.08 39.13 38.85 39.03 38.68CS-B06 37.94 37.91 38.54 37.62 39.37 38.28CS-B07 37.60 38.54 39.32 39.22 38.38 38.61CS-B16 38.21 39.76 38.60 39.84 40.49 39.38CS-B17 37.07 37.66 37.52 38.99 37.97 37.84CS-B18 38.16 39.69 39.42 39.73 39.17 39.23CS-B25 36.90 37.65 36.88 37.69 38.15 37.45CS-B05sh 37.80 38.80 39.76 38.16 39.56 38.82CS-B14sh 35.98 37.31 37.44 38.34 37.95 37.40CS-B15sh 37.05 37.87 37.61 37.36 37.87 37.55CS-B22sh 39.94 40.51 40.22 40.44 41.16 40.45CS-B22Lo 39.54 39.74 39.26 40.64 40.88 40.013–79 33.55 36.52 33.10 33.83 34.45 34.29Mean 37.45 38.49 38.15 38.56 38.79

†LSD 0.05 for comparing males averaged across cultivars is 0.30; LSD 0.05for comparing individual hybrids is 0.57; and LSD 0.05 for comparingfemale means averaged across CS-B lines, TM-1, and 3–79 individualhybrids is 0.15.

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1171JENKINS ET AL.: CSB TOPCROSSES COTTON

significantly greater than 39% and three significantlygreater than 40% (Table 2).The mean boll weight of hybrids with each cultivar

ranged from 5.23 to 5.89 g boll21 (Table 3). The hybridswith FM 966 had the heaviest bolls. When averagedacross cultivars, there were six CS-B hybrids with smallerbolls and two with larger bolls than hybrids with TM-1.All hybrids with 3–79 had boll weight less than or equalto 4.10 g; whereas, only hybrid ST 474 3 CS-B14sh hadboll weight less than 5 g. There were 61 hybrids with bollweight significantly greater than 5 g, and 4 hybrids withFM 966 with boll weight significantly greater than 6 g(Table 3).Mean seed cotton yields of hybrids with FM 966 were

significantly greater than hybrids with the other cul-tivars. This cultivar was also the highest in seed cottonyield. Among individual hybrid yields, the hybrid FM966 3 CS-B02, produced more seed cotton than anyhybrid except FM 966 3 CS-B22Lo. No CS-B hybrid

mean yield across cultivars was significantly greater thanthe TM-1 hybrid mean across cultivars and three wereless than TM-1 hybrids. The hybrids with 3–79 yieldedthe least seed cotton among all hybrids (Table 4).

The mean lint yields of hybrids with each cultivarranged from 1112 to 1315 kg ha21. The average yield ofhybrids with DP 90 and ST 474 was significantly lowerthan hybrids with the other three cultivars. The meanlint yield of hybrids with FM 966 was the highest. Con-sidering the means of hybrids across the five cultivars,hybrids with CS-B22Lo had lint yields significantlygreater than TM-1 hybrids; whereas, hybrids with CS-B16, CS-B18, and CS-B14sh had lint yields significantlyless than hybrids with TM-1. All 3–79 hybrids producedless than 600 kg ha21 of lint. There were 57 of the 75 hy-brids with lint yield significantly greater than 1000 andnine hybrids yielded significantly greater than 1200 kgha21 (Table 5). Thus, hybrids of elite cultivars with spe-cific CS-B lines offer a better opportunity to use genesfrom 3–79, G. barbadense to improve lint yields thancrosses of elite cultivars with the entire genome of 3–79.

Variance ComponentsWe expect that chromosome substitution lines (i.e.,

CS-B) when crossed with elite cultivars will reduce atrait’s phenotypic complexity when compared to inter-specific lineages with the same elite cultivars. This re-duction in phenotypic complexity will improve variancecomponent estimates.

The variance components were expressed as propor-tions of the phenotypic variance and are summarized inTable 6. Additive effects contributed the most to yieldand yield components (lint percentage 57.6%, bollweight 58.1%, seed cotton yield 37.7%, and lint yield41.9%). Dominance effects also made significant con-tributions to the phenotypic variance (lint percentage30.2%, boll weight 24.8%, seed cotton 15.9%, and lintyield 17.6%). The G 3 E interaction variance [(VAE 1VDE)/VP] contributed less than 10% to the phenotypic

Table 4. Seed cotton yields (kg ha21) of F2 hybrid from crosses offive cultivars with CS-B lines, TM-1, and 3–79.

CultivarMaleparent† DP90 SG747 PSC355 ST474 FM966 Mean

TM-1 3154 3495 3556 3093 3558 3371CS-B02 3300 3419 3334 3336 4055 3489CS-B04 2982 3255 3437 3300 3481 3291CS-B06 3228 3487 3525 3049 3609 3380CS-B07 3236 3472 3590 3110 3639 3409CS-B16 2369 3053 2438 2419 3039 2663CS-B17 3090 3150 3272 3290 3343 3229CS-B18 2953 3114 3097 2797 3257 3043CS-B25 3055 3338 3334 3250 3388 3273CS-B05sh 3285 3345 3538 3259 3730 3432CS-B14sh 2687 2989 3461 3048 3605 3158CS-B15sh 3445 3391 3432 3313 3507 3417CS-B22sh 3309 3041 3419 3306 3584 3332CS-B22Lo 3293 3440 3395 3127 3808 34133–79 1231 1468 1666 1366 1156 1378Mean 2974 3164 3233 3004 3384

†LSD 0.05 for comparing males averaged across cultivars is 183; LSD 0.05for comparing individual hybrids is 410; and LSD 0.05 for comparingfemale means averaged across CS-B lines, TM-1, and 3–79 individualhybrids is 105.

Table 5. Lint yield (kg ha21) of F2 hybrid from crosses of five cul-tivars with CS-B lines, TM-1, and 3–79.

CultivarMaleparent† DP90 SG747 PSC355 ST474 FM966 Mean

TM-1 1167 1318 1333 1187 1367 1275CS-B02 1233 1293 1265 1289 1570 1330CS-B04 1104 1264 1337 1272 1354 1266CS-B06 1217 1304 1351 1124 1415 1282CS-B07 1211 1331 1406 1199 1391 1308CS-B16 895 1206 935 952 1229 1043CS-B17 1134 1176 1225 1274 1266 1215CS-B18 1115 1227 1219 1096 1273 1187CS-B25 1123 1250 1219 1212 1286 1218CS-B05sh 1237 1283 1405 1228 1472 1325CS-B14sh 954 1109 1287 1156 1364 1174CS-B15sh 1276 1271 1284 1224 1325 1276CS-B22sh 1313 1222 1372 1321 1473 1340CS-B22Lo 1294 1348 1323 1256 1545 13533–79 413 535 549 462 397 471Mean 1112 1209 1234 1150 1315

†LSD 0.05 for comparing males averaged across cultivars is 70; LSD 0.05for comparing individual hybrids is 157; and LSD 0.05 for comparingfemale means averaged across CS-B lines, TM-1, and 3–79 individualhybrids is 41.

Table 3. Boll weight (grams seed cotton boll21) of F2 hybrid fromcrosses of five cultivars with CS-B lines, TM-1, and 3–79.

CultivarsMaleparent† DP90 SG747 PSC355 ST474 FM966 Mean

TM-1 5.42 5.70 5.67 5.42 6.09 5.66CS-B02 5.38 5.62 5.71 5.61 6.25 5.71CS-B04 5.36 5.66 5.70 5.76 6.32 5.76CS-B06 5.68 5.72 5.60 5.61 6.19 5.76CS-B07 5.59 5.61 5.35 5.43 5.94 5.58CS-B16 5.32 5.62 5.67 5.29 6.39 5.66CS-B17 5.51 5.68 5.57 5.42 6.11 5.66CS-B18 5.37 5.56 5.44 5.27 5.94 5.52CS-B25 5.27 5.42 5.04 5.33 5.89 5.39CS-B05sh 5.13 5.40 5.21 5.24 5.90 5.38CS-B14sh 5.05 5.17 5.09 4.75 5.69 5.15CS-B15sh 5.57 5.72 5.63 5.69 6.27 5.78CS-B22sh 5.44 5.34 5.19 5.35 6.11 5.49CS-B22Lo 4.91 5.17 5.29 5.04 5.60 5.203–79 3.50 4.10 3.44 3.38 3.62 3.61Mean 5.23 5.43 5.31 5.24 5.89

†LSD 0.05 for comparing males averaged across cultivars is 0.09; LSD 0.05for comparing individual hybrids is 0.19; and LSD 0.05 for comparingfemale means averaged across CS-B lines, TM-1, and 3–79 individualhybrids is 0.05.

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variance for lint percentage and boll weight and ac-counted for 24 and 22% to the phenotypic variance forseed cotton yield and lint cotton yield, respectively.Thus, the larger proportion of the phenotypic varianceattributed to additive effects, indicates that these effectscan be utilized in breeding programs designed to pro-duce cultivars. The significant dominance componentsalso indicate that specific CS-B lines may be useful fordeveloping hybrid cottons. In this present study, webridge across genetic interest to plant breeding interestas we probe the genetic effects of a specific 3–79 chro-mosome or chromosome arm and the homologous chro-mosome or arm in the elite cultivars.

Additive Genetic EffectsAdditive effects can be considered as measuring the

generalcombiningability(GCA)ofparentsandwereportthese as deviations from the population grand mean. Wecan also calculate the additive effects of only the specificchromosome or chromosome arm from 3–79 that is sub-stituted into the CS-B parent and this is calculated as thedifference in the additive effect value for a CS-B parentand the additive effect value for the TM-1 parent.

Lint Percentage

Additive effects for lint percentage were significantlydifferent from TM-1, but negative, for CS-B02, CS-B04,

CS-B07, CS-B25, CS-B05sh, CS-B14sh, and CS-B15sh.However, CS-B16, CS-B18, CS-B22sh, and CS-B22Lohad positive additive effects for lint percentage that weresignificantly greater than TM-1. Thus, alleles on chro-mosomes 16, 18, 22sh, and 22Lo from 3–79 contributegreater additive effects for lint percentage than alleleson the homologous chromosomes in TM-1 (Table 7).

Boll Weight

FM 966, the cultivar with the heaviest bolls, had thelargest additive effects (0.64 g boll21) for boll weight(Table 7). SG 747 also had significant positive additiveeffects; whereas, DP 90 and ST 474 had significant neg-ative additive effects on boll weight. Although eightCS-B lines had significantly lower boll weight than TM-1; additive effects for chromosomes 4, 6, and 15sh from3–79 were significantly greater than additive effects forhomologous chromosomes in TM-1; whereas, additiveeffects for boll weight for chromosomes 18, 25, 05sh,14sh, 22sh, and 22Lo from 3–79 were less than the ho-mologous chromosomes in TM-1. Additive effects for3–79 were negative and less than TM-1.

Seed Cotton Yield

Additive effects for seed cotton yield were positiveand significantly different than zero for all cultivars and

Table 6. Variance Components and standard errors expressed as proportions of the phenotypic variances for yield traits.

Lint % Boll weight Seed cotton yield Lint yield

VA/VP† 0.576 60.009 0.581 60.013 0.377 60.017 0.419 60.017VD/VP 0.302 60.011 0.248 60.016 0.159 60.021 0.176 60.021VAE/VP 0.007 60.002 0.000 60.000 0.105 60.010 0.097 60.009VDE/VP 0.061 60.009 0.079 60.016 0.135 60.024 0.124 60.022Ve/VP 0.054 60.005 0.092 60.005 0.224 60.022 0.184 60.021

†VA 5 additive variance;VD 5 dominance variance;VAE 5 additive3 environment variance;VDE 5 dominance3 environment variance;Ve 5 error variance;VP 5 phenotypic variance.

Table 7. Additive effects and standard errors for yield and yield components expressed as deviations from population grand mean.

Male parents Lint percentage † ‡ Boll weight † ‡Seed cotton

yield † ‡Lint cotton

yield † ‡

% g kg ha21 kg ha21

DP 90 1.64 60.12 ** * 20.09 60.03 ** * 236 659 ** * 135 622 ** *SG 747 2.56 60.09 ** * 0.11 60.03 ** 529 667 ** * 262 626 ** *PSC 355 2.31 60.10 ** * 0.01 60.02 * 575 678 ** * 283 631 ** *ST 474 2.18 60.10 ** * 20.09 60.03 * * 277 665 ** * 153 626 ** *FM 966 3.03 60.12 ** * 0.64 60.04 ** * 769 668 ** * 382 628 ** *TM-1 21.00 60.08 ** 0.19 60.03 ** 56 638 212 614CS-B02 20.78 60.07 ** * 0.25 60.03 ** 170 662 * 43 625CS-B04 20.35 60.08 ** * 0.29 60.03 ** * 229 658 221 623CS-B06 20.78 60.09 ** 0.29 60.03 ** * 51 675 28 628CS-B07 20.42 60.11 ** * 0.13 60.03 ** 85 666 19 625CS-B16 0.20 60.11 * 0.19 60.04 ** 2612 664 ** * 2233 626 ** *CS-B17 21.07 60.08 ** 0.20 60.03 ** 279 654 * 265 620 ** *CS-B18 0.17 60.10 * 0.06 60.03 * 2253 655 ** * 294 622 ** *CS-B25 21.53 60.12 ** * 20.07 60.02 ** * 238 682 265 631CS-B05sh 20.26 60.08 ** * 20.07 60.03 * * 108 680 36 631CS-B14sh 21.61 60.09 ** * 20.28 60.03 ** * 2140 656 * * 2106 622 ** *CS-B15sh 21.47 60.11 ** * 0.31 60.03 ** * 110 658 26 623CS-B22sh 1.33 60.11 ** * 0.03 60.03 * 21 659 54 624 * *CS-B22Lo 0.82 60.11 ** * 20.23 60.02 ** * 89 669 60 627 * *3–79 24.97 60.17 ** * 21.86 60.03 ** * 21922 664 ** 2816 624 ** *

* Significantly different at 0.05 probability level.** Significantly different at 0.01 probability level.†Difference from zero.‡Difference between CS-B line and TM-1.

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1173JENKINS ET AL.: CSB TOPCROSSES COTTON

CS-B02; however, no chromosome from 3–79 had ad-ditive effects significantly greater than additive effects ofthe homologous chromosome in TM-1. Additive effectson seed cotton yield for chromosomes 16, 17, 18, and14sh from 3–79 were negative and less than additiveeffects for homologous chromosomes from TM-1. Alarge negative additive effect on yield was found for thewhole genome 3–79 (Table 7).

Lint Yield

Additive effects on lint yield for all cultivars werepositive and greater than TM-1. Chromosomes 22shand 22Lo from 3–79 had positive additive effects thatwere significantly greater than the homologous chro-mosomes from TM-1; however, additive effects forchromosomes 16, 17, 18, and 14sh from 3–79 were nega-tive and less than the homologous chromosomes fromTM-1 (Table 7).

Dominance Genetic EffectsDominance effects can be considered as measuring

the specific combining ability (SCA) of parents in spe-cific hybrid combinations. We estimated two types ofdominance effects, homozygous (Dii) and heterozygous(Dij). A negative homozygous dominance effect for aparent will result in inbreeding depression in genera-tions following the use of this parent in a cross. Highheterozygous dominance effects between two parentsshould result in high heterosis in the F1 or F2 hybrid.The homozygous dominance effects are summarizedin Table 8 and the heterozygous dominance effects inTables 9–12.

Homozygous Dominance EffectsThe largest homozygous dominance effect among

cultivars for lint percent was ST 474 with positive3.3% (Table 8). This cultivar also had the highest lint

Table 8. Homozygous dominance effects and standard errors for yield and yield components expressed as deviations from population grandmean.

Male parents Lint percentage † ‡ Boll weight † ‡Seed cotton

yield † ‡Lint cotton

yield † ‡

% g kg ha21 kg ha21

DP 90 20.26 60.31 20.35 60.12 ** * 151 6236 * 72 697 *SG 747 0.53 60.39 * 20.30 60.10 ** 2443 6261 2106 6109PSC 355 20.05 60.37 20.46 60.09 ** * 2318 6312 287 6131ST 474 3.31 60.47 ** * 20.30 60.11 * 89 6265 185 6123 *FM 966 20.54 60.43 20.67 60.10 ** * 2579 6163 ** 2195 673 *TM-1 20.41 60.23 20.10 60.12 2507 6172 ** 2179 662 *CS-B02 20.58 60.23 * 20.23 60.13 2571 6188 ** 2229 673 **CS-B04 21.74 60.28 ** * 20.27 60.10 * 2219 6117 2121 648 *CS-B06 20.85 60.27 ** 20.31 60.12 * 2193 6259 287 697CS-B07 21.93 60.37 ** * 20.42 60.13 ** 2336 6185 2177 671 *CS-B16 0.60 60.26 * * 20.12 60.11 2256 6121 255 647CS-B17 24.05 60.29 ** * 20.56 60.09 ** * 2431 6151 * 2218 652 **CS-B18 21.91 60.30 ** * 20.25 60.14 2380 6162 * 2162 663 *CS-B25 21.65 60.40 ** * 20.22 60.10 * 2422 6228 2160 683CS-B05sh 21.28 60.31 ** * 20.33 60.08 ** 2423 6181 * 2205 671 *CS-B14sh 21.00 60.28 ** 20.56 60.09 ** * 2543 6163 ** 2178 659 **CS-B15sh 21.06 60.34 ** 20.43 60.09 ** * 2732 6147 ** 2266 652 **CS-B22sh 22.13 60.45 ** * 20.31 60.12 * 2536 6211 * 2283 687 **CS-B22Lo 20.08 60.21 20.51 60.10 ** * 2380 6182 2156 672 *3–79 9.10 60.26 ** * 1.94 60.06 ** * 2461 6261 ** * 1127 6100 ** *

* Significantly different at 0.05 probability level.** Significantly different at 0.01 probability level.†Difference from zero.‡Difference between CS-B line and TM-1.

Table 9. Heterozygous dominance effects and standard errors for lint percentage expressed as deviations from population grand mean.

Cultivar

Male parents DP90 SG747 PSC355 ST474 FM966

TM-1 0.15 60.44 20.39 60.34 20.66 60.23 0.57 60.50 0.12 60.36CS-B02 0.19 60.30 20.43 60.43 20.32 60.44 0.54 60.26 0.40 60.35CS-B04 20.47 60.33 1.08 60.40* 1.98 60.47* 0.04 60.34 0.51 60.40CS-B06 1.33 60.49 21.02 60.35 1.12 60.44* 22.20 60.43* 1.68 60.35*CS-B07 0.38 60.33 0.11 60.34 2.59 60.42* 1.05 60.52 20.69 60.34CS-B16 20.85 60.41 0.21 60.47 21.52 60.45 20.17 60.42 1.33 60.36*CS-B17 1.62 60.30* 0.59 60.40 1.09 60.45* 2.93 60.36* 0.80 60.42CS-B18 0.35 60.39 1.38 60.42* 1.58 60.33* 0.91 60.34 20.22 60.34CS-B25 1.03 60.39 0.36 60.47 20.51 60.30 20.11 60.50 0.97 60.42CS-B05sh 0.14 60.21 0.01 60.33 2.88 60.33* 21.93 60.28* 1.19 60.41CS-B14sh 21.14 60.47 20.54 60.36 0.52 60.44* 1.14 60.35 0.38 60.42CS-B15sh 0.92 60.35 0.41 60.38 0.62 60.41* 21.27 60.37* 20.06 60.39CS-B22sh 1.89 60.47* 0.83 60.42* 1.01 60.43* 0.13 60.44 1.78 60.37*CS-B22Lo 1.05 60.40 20.80 60.36 21.04 60.47 0.59 60.38 1.21 60.32*3–79 24.4 60.62* 20.25 60.73 26.87 60.56* 26.63 60.49* 25.2 60.41*

* Significantly different from TM-1 at 0.05 probability level.

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1174 CROP SCIENCE, VOL. 46, MAY–JUNE 2006

percentage among cultivars (Table 1). All CS-B lines(Table 8) had significant negative homozygous domi-nance effects for lint percentage except CS-B16 (10.60)and CS-B22Lo (not different from zero). Homozygousdominance effects for boll weight were negative for allcultivars and CS-B lines (Table 8). Homozygous dom-inance effects for seed cotton yield were similar to thosefor lint cotton yield. Homozygous dominance effects forlint yield for all CS-B parents were significant and neg-ative, except for CS-B6, CS-B16, and CS-B25, whichwere not different from zero. FM 966 had a significantnegative homozygous dominance effects whereas, theeffect for the other four cultivars were not significantlydifferent from zero (Table 8).

Heterozygous Dominance EffectsLint Percentage

In hybrids with DP 90, heterozygous dominance ef-fects for lint percentage for substituted chromosomes17 and 22sh were significantly greater than for the ho-mologous chromosome in TM-1 (Table 9). In hybridswith SG 747, dominance effects for substituted chromo-somes 4, 18, and 22sh were significantly greater than

homologous chromosomes in TM-1. In hybrids withPSC 355, dominance effects for substituted chromosome4, 6, 7, 17, 18, 05sh, 14sh, 15sh, and 22sh were sig-nificantly greater than homologous chromosomes inTM-1. In hybrids with ST 474, dominance effects forsubstituted chromosome 17 was significantly greaterthan chromosome 17 in TM-1; whereas, dominance ef-fects for substituted chromosomes 6, 5sh, and 15sh from3–79 were significantly less than the homologous chro-mosomes in TM-1. ST 474 had the highest lint per-centage among cultivars and CS-B17 had the lowest. Inhybrids with FM 966, substituted chromosomes 6, 16,22sh, and 22Lo had heterozygous dominance effectsfor lint percentage that were significantly greater thanthe homologous chromosomes in TM-1. These data in-dicate that specific substituted chromosomes from 3–79interact to provide significant, positive, heterozygousdominance effects greater than the homologous TM-1chromosome and much better than the negative dom-inance effects from the whole genome 3–79 crosses.Thus, these effect are essentially the heterozygous domi-nance effects of alleles on individual chromosomes from3–79 with the homologous chromosome in cultivars orthey could be viewed as chromosome specific heterozy-

Table 10. Heterozygous dominance effects and standard errors for boll weight expressed as deviations from population grand mean.

Cultivar

Male Parents DP90 SG747 PSC355 ST474 FM966

TM-1 20.05 60.10 0.12 60.14 0.35 60.16 20.08 60.15 0.05 60.10CS-B02 20.19 60.11 20.11 60.13 0.38 60.14 0.28 60.10 0.35 60.14CS-B04 20.32 60.13 20.09 60.10 0.28 60.09 0.52 60.08* 0.43 60.11*CS-B06 0.39 60.15* 0.06 60.11 0.07 60.12 0.22 60.13 0.17 60.17CS-B07 0.57 60.14* 0.21 60.16 20.07 60.12* 0.23 60.13 0.02 60.16CS-B16 20.25 60.15 20.05 60.13 0.36 60.11 20.35 60.13 0.72 60.11*CS-B17 0.33 60.06* 0.26 60.11 0.32 60.11 0.12 60.13 0.31 60.10CS-B18 0.17 60.17 0.17 60.19 0.19 60.15 20.05 60.16 0.09 60.17CS-B25 0.19 60.14 0.09 60.10 20.43 60.14* 0.30 60.14 0.22 60.16CS-B05sh 20.03 60.17 0.13 60.13 0.01 60.14 0.18 60.11 0.30 60.10CS-B14sh 0.33 60.11* 0.16 60.11 0.28 60.15 20.33 60.13 0.39 60.17CS-B15sh 0.17 60.19 0.07 60.10 0.16 60.13 0.40 60.17* 0.37 60.17CS-B22sh 0.40 60.15* 20.22 60.16 20.27 60.10* 0.20 60.13 0.54 60.14*CS-B22Lo 20.09 60.10 0.05 60.13 0.59 60.12 0.16 60.08 0.08 60.123–79 21.01 60.16* 20.15 60.18 21.27 60.16* 21.28 60.15* 22.06 60.19*

* Significantly different from TM-1 at 0.05 probability level.

Table 11. Heterozygous dominance effects and standard errors for seed cotton yield in kg ha21 expressed as deviations from populationgrand mean.

Cultivar

Male parents DP90 SG747 PSC355 ST474 FM966

TM-1 72 6216 470 6257 441 6353 2101 6190 187 6164CS-B02 170 6282 136 6272 2193 6281 199 6301 999 6288*CS-B04 2247 6301 16 6223 236 6206 341 6196 645 6184CS-B06 76 6242 312 6213 238 6209 2335 6208 147 6353CS-B07 99 6259 288 6267 371 6182 2210 6225 211 6255CS-B16 2318 6173 771 6231 2616 6326* 2269 6198 337 6201CS-B17 165 6245 7 6251 99 6278 524 6152* 29 6213CS-B18 208 6245 249 6250 65 6296 2151 6201 137 6235CS-B25 12 6193 299 6301 141 6333 357 6181 23 6283CS-B05sh 186 6199 22 6222 268 6282 87 6338 392 6384CS-B14sh 2462 6217 2141 6164* 649 6327 213 6243 689 6261CS-B15sh 661 6221 271 6233 202 6257 346 6196 92 6255CS-B22sh 458 6362 2351 6215* 246 6274 410 6216 328 6204CS-B22Lo 223 6163 237 6245 211 6273 2164 6310 565 62733–79 21371 6131* 21174 6193* 2929 6181* 21147 6195* 22211 6229*

* Significantly different from TM-1 at 0.05 probability level.

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1175JENKINS ET AL.: CSB TOPCROSSES COTTON

gous dominance effects. Thus, these data show that wecan use specific chromosome substitution lines in crosseswith cultivars and overcome the negative dominanceeffects on lint percentage obtained when the whole ge-nome of 3–79 is used in crosses. This should also avoidthe hybrid incompatibility of the interspecific genomecross between G. hirsutum and G. barbadense.

Boll Weight

When the entire genome of 3–79 was crossed witheach cultivar, heterozygous dominance effects were verynegative and less than TM-1 for all hybrids, except withSG747 (Table 10). In hybrids with DP 90, substitutedchromosomes 6, 7, 17, 14sh, and 22sh from 3–79 had het-erozygous dominance effects significantly greater thanthe homologous chromosomes from TM-1 (Table 10).No chromosomes showed heterozygous dominance ef-fects different from TM-1 in hybrids with SG 747. Inhybrids with PSC 355, substituted chromosomes 7, 25,and 22sh had heterozygous dominance effects that werenegative and significantly less than homologous chro-mosomes fromTM-1. In hybrids with ST 474, substitutedchromosomes 4 and 15sh had positive heterozygousdominance effects significantly greater than homologouschromosomes from TM-1. In hybrids with FM 966, chro-mosomes 4, 16, and 22sh from 3–79 had positive het-erozygous dominance effects significantly greater thanhomologous chromosomes from TM-1. Breeders shouldbe able to increase boll weight of hybrids by using specificCS-B lines in crosses with DP 90, ST 474, and FM 966.

Seed Cotton Yield

All hybrids with 3–79 exhibited large, significant, neg-ative heterozygous dominance effects for seed cottonyield (Table 11). Crosses of ST 474 3 CS-B17 and FM9663 CS-B02 had positive heterozygous dominance forseed cotton yield which were greater than the homol-ogous chromosomes from TM-1, even though the crossof the entire genome of 3–79 with cultivars has a largenegative effect on seed cotton yield (Table 11).

Lint Cotton Yield

All hybrids with 3–79 exhibited large and negativeheterozygous dominance effects for lint yield (Table 12).Hybrids of DP 90 3 CS-B15sh, ST 474 3 CS-B17, andFM 966 3 CS-B02 exhibited large and positive dom-inance effects for lint yield which were greater thancorresponding hybrids with TM-1. The final product islint yield and in these three hybrids, chromosomes, 2,15sh and 17, from 3–79 contributed alleles that producedsignificantly greater heterozygous dominance effects forlint yield than alleles from the homologous chromo-somes in TM-1.

CONCLUSIONSWe can consider additive effects as representing GCA

effects and heterozygous dominance effects as SCAeffects. The five cultivars, as expected, had larger addi-tive effects for lint percentage and lint cotton yield thaneach of the CS-B lines, indicating that these cultivarswere good combiners for improving lint percentage andlint cotton yield compared to these CS-B lines. All wholegenome F2 hybrid lines involving 3–79 displayed “hybridbreakdown” typical for F2 populations between thesetwo species. This hybrid breakdown is accompanied bypartial sterility, poor seed viability, and other disrup-tions. The incompatibility between these two speciesmay not necessarily affect specific yield related genes,but could be the result of disruption of regulatory genesdetermining fertility, seed viability, etc. The value ofthe CS-B lines is that they allow chromosome specificgenetic effects to be dissected from the 3–79 genome andutilized for improvements in yield components andlint yield.

Chromosomes 22sh and 22Lo from 3–79 are goodexamples of small but significant increases of 54 and60 kg lint ha21 because of additive effects. Three specificcrosses involving chromosomes 2, 17, and 15sh from 3–79 are examples of significant heterozygous dominanceeffects for lint yield of 396, 273, and 274 kg lint ha21,respectively. These chromosome specific positive ef-fects indicate that the CS-B lines can provide access to

Table 12. Heterozygous dominance effects and standard errors for lint cotton yield in kg ha21 expressed as deviations from populationgrand mean.

Cultivar

Male parents DP90 SG747 PSC355 ST474 FM966

TM-1 18 685 161 6100 140 6141 235 679 62 667CS-B02 67 6112 28 6109 284 6112 95 6124 396 6118*CS-B04 2121 6116 41 691 140 683 132 680 28 676CS-B06 67 693 79 681 124 684 2215 679 109 6145CS-B07 47 6102 123 6110 227 678 271 692 49 6103CS-B16 2160 669 309 695 2298 6130* 2136 684 160 685CS-B17 75 693 24 6102 44 6109 273 662* 216 687CS-B18 67 696 134 6103 62 6123 262 682 29 698CS-B25 24 675 116 6119 2 6127 115 670 24 6112CS-B05sh 76 678 40 690 205 6116 233 6133 196 6159CS-B14sh 2232 684* 282 667* 231 6127 90 697 245 6103CS-B15sh 274 687* 96 691 72 6100 75 675 10 6102CS-B22sh 235 6151 2115 688* 137 6115 162 692 200 688CS-B22Lo 121 668 66 699 239 6112 249 6133 273 61163–79 2567 642* 2482 677* 2506 670* 2558 671* 2964 687*

* Significantly different from TM-1 at 0.05 probability level.

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useful QTL alleles in G. barbadense 3–79 that are noteasily detectable or useful at the whole genome cross.Chromosomes 16, 18, 22sh, and 22Lo showed signifi-cant, positive additive effects for lint percentage, 22shand 22Lo showed significant and positive additive ef-fects for lint yield, and chromosomes 4, 6, and 15sh hadsignificant and positive additive effects for boll weightthat were each greater than the respective additive ef-fects of TM-1. These are specific examples of allelesfrom specific chromosomes or arms of 3–79 that areuncovered in the CS-B lines and that were better thanalleles in TM-1. Considering that 3–79 has a smallerboll and produces less lint yield than TM-1 this illus-trates the utility of using CS-B lines to uncover usefulgenetic alleles.Thefivecultivarsusedinthesecrossesrepresentdiverse

commercial breeding programs; therefore, the resultsfrom these studies should offer guidance to commercialuse of these CS-B germplasm in breeding programs.Jenkins et al. (2004) reported that chromosome 25 of

3–79 had greater additive effects on fiber length andfiber strength and chromosome arms 22sh and 22Lo hadgreater additive effects for lint percentage and lint yieldthan the homologous chromosomes in TM-1 and thatmost traits showed predominantly additive effects, usingdata from two environments, for the same top crossesused in this present study. In the current study, weexpanded the environments to four and thus obtained abetter estimate of these effects.Plant breeding improvements from whole genome

crosses between G. barbadense and G. hirsutum havenot been very successful because of incompatibility andother genetic problems. However, use of these CS-Blines allows alleles from single G. barbadense chromo-somes to be introgressed into G. hirsutum while avoid-ing the major problems common to interspecific crossesbetween these species. These CS-B lines provide a betterway to use the favorable alleles from G. barbadense.CS-B lines allow the effects of an individual chromo-somes or chromosome arms to be studied. Recombinantsubstituted (RS) lines, which are recombinant inbredlines for specific chromosomes, can be used to moreprecisely identify and map gene(s) controlling agro-nomic traits, fiber traits, and to map molecular markers(Campbell et al., 2003, 2004; Kaeppler, 1997; Shah et al.,1999). RS lines are superior to recombinant inbred linesfor identifying genes or QTL of quantitative traits be-cause RS lines increase statistical power and have amoreuniform genetic background with only one divergentchromosome or segment. We are developing RS pop-ulations in selected CS-B lines to be used for high-resolution dissection andmapping of theQTL governingcotton yield and fiber quality.

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1178 CROP SCIENCE, VOL. 46, MAY–JUNE 2006