Comparative,performanc.of,hybrid,generations,reveals,the,potential,applicatio.of,F2,hybrids,in,upland,cotton

时间：2023-01-21 19:00:05　来源：天一资源网本文已影响人

CHEN Liangliang, TANG Huini, ZHANG Xuexian, QI Tingxiang, GUO Liping, SHAHZAD Kashif, WANG Hailin, QIAO Xiuqin, ZANG Rong, ZHANG Meng, WU Jianyong and XING Chaozhu

Abstract Background: The utilizatio.of heterosis has greatly improved the productivit.of cotton worldwide. However, a major constraint for the large-scale promotio.of F1 hybrid cotton is artificial emasculation and pollination. This study proposed the potential utilizatio.of F2 hybrids to improve upland cotton production through a comparative evaluatio.of hybrid generations.Results: Eight upland cotton varieties were analyzed and crosses were made according to NCII incomplete diallel cross-breeding design in two cotton belt.of China. Variance analysis revealed significant differences in agronomic, yield, and fiber quality in both generations and environments. The broad-sense heritabilit.of agronomic and yield traits was relatively higher than quality traits. Furthermore, the narrow-sense heritabilit.of some traits was higher in F2 than in the F1 generation in both cotton belts. Overall, parental lines Zhong901, ZB, L28, and Z98 wer.observed with maximum combining ability while combinations with strong special combining ability were ZB × DT, L28 × Z98, and ZB × 851. The yield traits heterosis was predominant in both generations. However, the leve.of heterosis was altered with trait, hybrid combination, generation, and environment. Interestingly, L28 × Z98 performe.outstandingly in Anyang. Its lint yield (LY) was 24.2% higher in F1 an.11.6% in F2 than tha.of the control Ruiza 816. The performanc.of SJ48 × Z98 was excellent in Aral which showe.36.5% higher LY in F1 an.10.9% in F2 than control CCRI 49. Further results revealed most hybrid combinations had shown a low leve.of heterosis for agronomic and fiber quality traits in both generations. Comparatively, ZB × DT and L28 × Z98 showed hybrid vigor for multiple traits in both generations and cotton belts. It is feasible to screen strong heterosis hybrid combinations with fine fiber in early generations. In the two environments, the correlatio.of some traits showed the same trend, and the correlation degre.of Anyang site was higher than tha.of Aral site, and the correlatio.of some traits showed th.opposite trend. According to the performanc.of strong heterosis hybrid combinations in different environments, the plant type, yield and fiber traits associated with them can be improved according to the correlation.Conclusions: Through comparative analysi.of variance, combining ability, and heterosis in F1 and F2 hybrids in different cotton belts, this study proposed the potential utilizatio.of F2 hybrids to improve upland cotton productivity in China.

Keywords: Upland cotton, F2 generation, Combining ability, Heterosis, Heritability

Heterosis is a phenomenon by which hybrid progenies show superior performance compared to theirs in the aspec.of vegetative growth, reproductive growth, and stress tolerance (Shahzad et al. 2019a). Hybrids have widely been used to improve the crop yiel.of agronomic and horticultural crops including rice (Li et al. 2016), maize (Yu et al. 2021), tomato Yu et al., 2020), kohlrabi (Singh et al. 2019). The utilizatio.of heterosis increased th.10%～20% yiel.of hybrid rice (Oryza sativa) more than conventional cultivars (Luo et al. 2013). The soybean hybrids produce.15%～25% more yield compared with conventional varieties (Wang et al. 2002). At present, about 80%～90.of vegetable varieties are hybrids. Even countries such as the Netherlands, the United States, and Israel have more developed hybrid vegetable seed industries. Utilizing heterogeneity is an extremely important genetic improvement technique to boost yield, quality, and resistance to diseases, insects, and pests. Global warming is a major threat to sustainable yield in recent years. Therefore, heterosis has the important practical significance in meeting market demand, improving economic efficiency, and ensuring food security.

Cotton is a major economic crop that has no.only a renewable natural textile fiber source but als.owns an ample amoun.of vegetabl.oil resources (Chen et al. 2007). Approximately 90.of the world cotton yield comes from upland cotton (Gossypium hirsutumL.) while Egyptian cotton (Gossypium barbadenseL.) produce.onl.3% fiber (Fang et al. 2017). The upland cotton has shown significant heterosis for yield traits and altered across various traits, stages, and environments (Schnable et al. 2013). Moreover, hybrid cotton could be more adaptable and stable in varying environments (Shahzad et al. 2019b). Cotton hybrids have been devolved through the utilizatio.of heterosis in China and planted in the main cotton provinces such as Hubei, Hunan, and Jiangxi. The are.of hybrid cotton planted was about 70.of the total cotton grown in these provinces (Xing et al. 2017). Heterosis has become a crucial way to increase cotton yield and improve fiber quality. Selecting and promoting hybrid cotton with strong heterosis have a meaningful impac.on cotton production in China. However, artificial emasculation seed production is the main way to utilize cotton heterosis. Due to the high cos.of seed production, the utilizatio.of F1heterosis is largely restricted to vast hybrid commercialization. To mitigate this challenge, the promotion and applicatio.of hybrid cotton increased rapidly with the expansio.of cotton planting area in Xinjiang, and people gradually shift their attention to using the F2generatio.of cotton hybrids.

Many cotton breeders have already proposed the utilizatio.of F2cotton hybrids to reduce the cos.of seed production and to meet the demand.of cotton growers in diverse ecological environments. A large numbe.of research findings showed that F2hybrids still have certain competitive advantage.over inbred parents (Meng et al. 2019; Chen et al. 2021). Combining ability is an important index to determine the transmission abilit.of excellent characters, to correctly evaluate the advantages and disadvantage.of combinations, and to select excellent parents and hybrid combinations to boost the efficienc.of any breeding program (Wang et al. 2012; Liu et al. 2019; Shi et al. 2021). In this study, eight upland cotton varieties were selected as experimental materials and crosses were made according to the NC II incomplete diallel cross (5 .3) breeding design. The performance, combining ability, and heterosis were analyzed in F1and F2hybrids for multiple traits and locations. The mai.objectiv.o.our study is to compare F1and F2hybrids and combine them with the breeding practic.of strong hybrid cotton to select the best combinatio.of heterosis and provide a reference for the feasibilit.of parental selection and utilizatio.of F2heterosis in China.

Experimental materials and field design

The field tests were conducted from 2020 to 2021. Al.15 F1hybrid combinations used in this study were produced by adopting North Carolina mating design II by crossing five upland cotton inbred lines as the female parents with three different inbred lines as the male parent with different nuclear backgrounds which have been reported i.our previous studies (Li et al. 2019; Shahzad et al. 2019b). Specifically, the inbred lines Zhong 901 (P1), ZB (P2), SJ48 (P3), L28 (P4), and K8 (P5) were used as female parents, while DT (P6), Z98 (P7), and 851 (P8) were used as male parents. In 2020, eight parental inbred lines an.15 F1hybrid combinations were planted in the east experimental field.of Institut.of Cotton Research Institut.of the Chinese Academ.of Agricultural Science, Anyang, Henan Province, China (36°10′N.114°35′E). All hybrids were self-pollinated and harvested t.obtain correspondin.15 F2hybrids (Tabl.1). In 2021, eight parents.15 F1and F2hybrid combinations were planted in two different cotton belt.of China, i.e., in Anyang which is located in Henan, and in Aral which is located in Xinjiang (40°55′N, 81°28′E). Ruiza 816 and CCRI 49 were used as the control varieties in Anyang and Aral, respectively. All experimental materials were planted in a randomized complete block design, wit.3 replicates. In Anyang, each material was planted in four rows without mulching, and in Aral adopts film mulching, and each material was planted unde.one film with six rows. Each block was 9.6 m2, and guard rows were set up around. The density was set according to the different ecological environment types, as 45000 plants per hectare in Anyang, an.150000 plants per hectare in Aral. Seeds were sown in late April in sequential years and the crop management practices followed the local recommendations.

Tabl.1 Code number.of al.15 hybrid combinations and their inbred parents

Investigation and method.of phenotypic traits

In mid-September, the plant height (PH), the heigh.of first fruit branch (HFFB), lengt.of first fruit branch (LFFB), the second fruit branch length (SFBL), fruit branch number (FBN), and boll number (BN) for each plant were investigated. When more than 90.of bolls ha.opened.one fully-opened boll was randomly selected from eac.of 50 individual plants and weighed to estimate boll weight (BW). The weigh.of seed cotton per plot was used to calculate seed cotton yield (SCY) and lint yield (LY) per hectare, and the lint percentage (LP, the rati.of the fiber weigh.on the seed cotton to the weigh.of the seed cotton). Subsample.of lint collected from each plot were sent to the Cotton Fiber Quality Testing Center affiliated with the Chinese Ministr.of Agriculture and Rural Affairs (Anyang, Henan) to assess fiber quality by using a High Volume Instrument (HVI_900) machine. Following data were captured: fiber length (FL, mm; upper half mean length), fiber uniformity (FU, %), fiber strength (FS, cN·tex-1), micronaire (MIC), and fiber elongation (FE, %). Also, we denoted SCY, LY BN, BW, and LP as yield traits; PH, HFFB, LFFB, SFBL, and FBN as agronomic traits; FL, FU, FS, FE, and MIC as fiber traits.

Data analysis

The test data were sorted and tabulated by Microsoft Excel, analysi.of variance, combining ability (i.e., General combining ability, GCA; Special combining ability, SCA), and heritability analysis (i.e., broad-sense heritability, H2; narrow-sense heritability, h2) with DPS software. Correlation analysis was performed with IBM SPSS statistics 25.0 software and Origin 2021 was used for figure drawing. The heterosis calculation base.on the mea.of parents (MP) and higher parent (HP) with the heterosis formula as follows: mid-parent heterosis (MPH) = (F1/F2-MP)/MP .100%, better-parent heterosis (BPH) = (F1/F2-HP)/HP .100%, competitive heterosis (CH) = (F1/F2-CK)/CK .100%, heterosis decline (HD) = (F1-F2)/F1.100%.

Variance analysi.of F1, F2 hybrids, and their inbred parents in different cotton belts

The variance analysis was performed fo.15 F1, and F2hybrids, and their eight inbred parents. The variance was extremely significant (P＜0.01) for the majorit.of traits in different cotton belts (Tables 2 an.3). All agronomic, yield, and fiber quality traits except FU and FE showed significant differences in F1generation among the combinations in Anyang (Table 2). Similarly, the differences among the combination.of F2generation reached significan.or extremely significant for all traits which indicated that the differences in these traits were mainly caused by genetic variation. The male inbred lines had a nonsignificant variance in LFFB and SFBL in both F1and F2generations. In contrast, male inbred lines demonstrated significant variance for the majorit.of yield and fiber quality traits in both generations. The male variance was extremely significant and improved in F2generation for SCY, LY, BN, BW, LP, and FL. Furthermore, male inbred lines exhibited significant differences for PH, SFBL, FE, and F.only in F2as compared with the F1generation. The female inbred lines had a significant variance in eight trait.of the F1generation, while the difference was significan.only in seven trait.of the F2generation. The female × male interaction variance was significant for the majorit.of traits in both generations except HFFB, FE, and MIC. Tabl.3 summarized the analysi.of variance results for all traits in Aral. All combinations in F1displayed extremely significant differences in agronomic and yield traits, whereas FL and FS-related fiber quality traits had significant differences. Similarly, F2only showed extremely significant differences in agronomic and yield trait.other than BN. The variance was significant among male parents for mos.of the traits in the F1generation specifically in LFFB, SFBL, SCY, LY, BN, LP, FL, FS, and MIC. The variance for female inbred was inconsistent between the two generations for 80.of agronomic and some yield traits. For example, LP had a highly significant difference in the F1generation. In contrast, PH, HFFB, SFBL, and FE had significant differences in F2. Interestingly, the female × male interaction variance was extremely significant for PH, HFFB, LFFB, FBN, and BW in F1and F2.

Table 2 Analysi.of variance and heritability analysi.of each trait in Anyang

Tabl.3 Analysi.of variance and heritability analysi.of each trait in Aral

Heritability analysi.of F1, F2 hybrids, and their eight inbred parents in different cotton belts

Heritability estimates the rati.of genetic variance to phenotypic variance. The broad-sense heritability (H2) and narrow-sense heritability (h2) were determined for all traits. Heritability analysis with Anyang was detailed in Table 2. According to the results, the percentag.of H2was strong for the majorit.of traits in both hybrid generations. In particular, LFFB, SFBL, FBN, SCY, LY, BW, LP, and FL stated that H2is greater than 70% in both hybrid generations. Conversely, FU had a lower percentag.of H2relative t.other traits in both hybrid generations. Further results determined that h2was strong and above 50% HFFB, SCY, LY, BW, LP, and FL in both F1and F2hybrids. LFFB and FU had very low h2in both generations than al.other traits. Heritability analysis for Aral detected that H2for PH, LFFB, SFBL, and BW was great than65% in both F1and F2. The heritabilit.of fiber traits in Aral was relatively lower than in Anyang. Specifically, FU and FE had low h2, which was less than 20% in F1and F2. Interestingly, the h2of some traits in the F2generation was higher than that in the F1generation. For instance, SCY, BW, LP in Anyang and LY in Aral had higher h2, in F2with more than 50%. These findings put forth a clue that it is significant to select these traits in the F2generation. The traits with lower heritability can easily be affected by the environment. Hence, these traits can be improved through longer screening cycles during breeding measures.

General combining ability analysi.of inbred parents in different cotton belts

General combining ability analysis is useful to screen superior inbred parents for specifi.or a se.of traits. Base.on the result.of combining ability analysis, the GC.of the parental line was different and altered with generation, trait, and environment (Table 4). In Anyang, parental lines P1, P4, and P7 their GCA for SCY and LY were positive in both hybrid generations. Furthermore, these parental lines comparatively had better GCA manifestation fo.other traits in F1and F2. In particular, P1 showed positive GCA for HFFB, LFFB, SFBL, SCY, LY, BN, and MIC. P4 had greater GCA for SCY, LY, BW, LP, and FU. P7 showed superior GCA for SCY, LY, BN, BW, LP, FU, and MIC. Apart from these inbred lines, P6 had better GCA for SCY, BW, FL, FE and PH, and HFFB. P2 and P8 exhibited positive GCA in fiv.or more agronomic characteristics and fiber quality traits. For P2 in PH, LFFB, SFBL, FBN, LP, FU, FE and MIC, and for P8 in LFFB, SFBL, FBN, FL and FS. It wa.observed that GCA was quite undulating in Aral. The parental lines P2, P4, and P7 were detected with positive GCA for SCY and LY in both F1and F2. P2 GCA was specifically well in many traits such as PH, LFFB, SFBL, FBN, SCY, LY, BN, FL, FU, FE, and FS. P4 showed better GCA for SFBL, FBN, SCY, LY, BW, LP, and FL. GC.of P7 was strong for SCY, LY, BN, LP, and MIC. In addition, P8 showed better GCA in six traits and had greater value in LFFB and SFBL. Overall, the GC.of P4 was improved for PH, LFFB, FBN, LY, BW, LP, FE and MIC in F2than F1in both cotton belts. However, seven trait.of GC.of P6 in F2were improved in both cotton belts. The P7 showed higher GCA in F2for SCY, LY, and BN in Anyang while P5 had improved GCA in F2for LFFB and SFBL in Aral. These results revealed the importanc.of these inbred lines to improve specific trait.or set.of traits in different cotton belts.

Special combining ability analysi.of F1 and F2 hybrids in different cotton belts

The SCA revealed the performanc.of a cross and provide a.opportunity for the utilizatio.of heterosis in crop breeding. The SC.of all combinations was altered with traits and environments (Tables 5 and6). In Anyang, it wa.observed that combinations6, 8, 9.10.12.13, an.14 have fiv.or more than five traits with SCA values greater than zero in both generations. Among these, combinations 9.10, an.12 all had positive SCA for SCY and LY in both F1and F2hybrids. Besides, combination 9 had also shown positive SCA for LFFB, BN, BW, FE, and MIC, and the SCA value.of combinatio.10 were positive for BW, LP, FL, and FS. Meanwhile, combinatio.12 had better performances with positive SCA for LFFB, SFBL, BN, BW, FL, and FS (Table 5). The SCA analysis results in Aral were shown in Table6. Among all combinations.only 2, 8, an.1.of SCY and LY were detected to be positive for SCA in both F1and F2. In particular, combination 2 had shown higher SCA for nine traits including SCY, LY, BW, LP, FL, FU, FE, FS, and MIC. Interestingly, the SC.of this combination was improved in F2for FL, FU, FE, and FS. It wa.observed that Combination 8 showed better performance as well as positive SCA for SCY, LY, BW, LP, FU, and FE. Combinatio.11 exhibited positive SCA in eight traits including PH, HFFB, FBN, SCY, LY, BW, FE, and MIC. Besides these, combination.3,6, 9.14, an.15, had positive SCA for mos.of the traits in F2as compared to F1. These combinations most probably can be selected in the F2breeding generation to improve these traits in Aral. Overall, analysis results revealed that combinations 9 and 2 had improved performance in F2in both cotton belts which emphasizes the selectio.of these combinations in earlier generations would be effective for the future breeding program.

The screenin.of hybrids with excellent heterosis in multiple traits

In this study, the leve.of MPH, BPH, CH, and HD for different traits, hybrid combinations, and in different cotton belts were analyzed. The analysis results revealed that the leve.of heterosis altered with the trait, hybrid combination, generation, and environment (Additional fil.1). The majorit.of combinations in Anyang had shown the highest heterosis for yield traits as compared to agronomic and fiber quality traits. For instance, in the F1generation, combinatio.12 exhibited the highest MPH (45.9%) for LY, and the L.of combination6 had the highest BPH a.36.3%. Moreover, the highest CH was 28.4% which had shown by combination 7 for BN. Most combination.of HD were positive for yield traits but negative for agronomic and fiber quality traits. It may be becaus.of the negative MPH, BPH, and CH in agronomic and fiber quality traits. Among F2generation, the L.of combinations 5.1, and 9 witnessed the highest MPH (24.0%), BPH (20.9%), and CH (11.6%) values, respectively. Intriguingly, combination 9 ha.outstanding MPH, BPH, and CH in multiple traits as compared t.other combinations. The analyzed results in Aral showed F1had the highest CH for LY (36.5%). This was exhibited by combination 8. However, combination 2 had the highest MPH (21.9%) and BPH (19.7%) for SCY amon.others. Besides this, a positive HD was measured for most yield traits among all hybrid combinations. While agronomic and fiber quality traits had negative HD in most hybrid combinations. The results revealed hybrid combinations had shown positive MPH, BPH, and CH for yield traits in the F2generation. Interestingly, combinations 2 and 9 had show.outstanding heterosis in multiple traits in Aral (Additional fil.1). Th.overall analysis determined that combination 9 had the best hybrid vigor in both generations and cotton belts. Therefore, it can be considered a.outstanding hybrid for both cotton zones.

Subsequently, this study further screened the top eight hybrid combinations with superior performance in multiple traits. The results revealed CH, MPH, and BPH in selected hybrids were altered with generation and cotton belts (Fig.1, Additional file 2). It was determined that more than6 combinations had better CH, MPH, and BPH in both generations and cotton belts. However, some combinations had superior CH, MPH, and BPH in both generations bu.one cotton belt. In this regard, combinatio.12 had similar performance in Anyang while combination 2 and combination 9 in Aral. Besides this, some combinations exhibited strong vigor in both cotton belts bu.only i.one generation. Such as combination 2 and combination 7 had shown better CH, MPH, and BPH in F1. Combination 9 displayed better CH, MPH, and BPH in F2. Comparatively, combinations 2 and 9 showed excellent performance in multiple traits for both generations and cotton belts. These encouraging results evaluate the potentia.of F2hybrids to improve cotton productivity in China.

Fig. 2 Correlation analysi.of yield, fiber, and agronomic traits in two ecological sites. Correlation analysis amon.15 traits in Anyang (A) and Aral (B).* and** show significant differences at0.05 and0.01 levels, respectively

Fig.1 Upset plot showing the detail.of the top eight hybrid combinations in BPH (A), CH (B), and MPH (C) for the F1 and F2 trait.of the two environments. The connectio.of the black circle in the figure represents the intersection between the different groups, and the numbe.of intersections is correspondingly represented in the upper bar chart

Correlations among various traits in two different cotton belts

The relationship between traits is a dynamic factor in the selectio.of plant breeding materials. The correlation analysis between agronomic, yield, and fiber quality traits in Anyang was summarized in Fig. 2A. A significant positive correlation wa.observed among yield (SCY, LY) and yield components (BN, BW, LP). All fiber quality traits except FU showed a negative correlation with yield traits. A significant positive correlation between FU and yield was detected. The correlation between yield and agronomic traits was either non-significant negativ.or positive. Similar results wer.observed among mos.of the fiber quality and agronomic traits. Most fiber quality traits including FL, FE, and FS had a positive correlation with eac.other. However, MIC had a strong negative correlation with FL and FS but a positive correlation with FU. The correlations were undulating among agronomic traits. For instance, PH had a significant negative correlation with LFFB and MIC but had a significant positive with FBN and FS. A significant positive correlation wa.observed between SFBL and LFFB.

The correlation analysis in Aral revealed SCY had a significant positive correlation with LY and BN whereas LY was positively correlated with BN and BW (Fig. 2B). The correlatio.of BW was significantly positive for FE and MIC. LP showed a significant negative correlation with FL and FS. In contrast, it had a significant positive correlation with MIC. Among fiber quality traits, FL had a significant positive correlation with FE and FS. MIC had a significant negative relationship with FL and FS. The agronomic traits had shown diverse correlations but few were significant. For instance, PH had an extremely positive correlation with HFFB, FBN, and FL. And PH negatively correlated with LP and MIC. Moreover, SFBL positively correlated with FS. FBN positively correlated with FL and FE. Overall, analysis results propose that agronomic, yield, and fiber quality traits can be improved independently in both cotton belts.

Cotton plays a critical role in textile industry development, employmen.opportunity, and foreign exchange earnings. Genotypes with higher yield and fine fiber are desired in upland cotton. This synchronized improvemen.of multiple traits in upland cotton demands more crossing, assessment, screening, and useful resources. The utilizatio.of heterosis is the most suitable method to achieve such vast breeding aims. Worldwide, difficulties in producing F1hybrid seeds have restricted the commercial us.of heterosis in cotton. However, this study compared the performance, combining ability, and heritability in both F1and F2generations in two cotton belts. Further the potential utilizatio.of F2hybrids was screened and discussed to improve cotton production in China.

Parental selection has critical importance in hybrid cotton breeding. However, the identificatio.of potential parents is a laborious job. In the utilizatio.of heterosis, selected parental materials should have superior performance, physiology, combining ability, and heritability. GCA refers to the average performanc.of a parental line in hybri.offspring and mainly anticipates the rol.of heritable additive genes contribution (Liu et al. 2019; Shang et al. 2012). Therefore, statistic.of GCA determined the selectio.of parental lines in the future breeding program. Previous studies have already shown that parents with high GCA can be well exploited through heterosis to produce superior hybrids (Hassan et al. 2000; Lukonge et al. 2008). I.our study, GCAs in the majorit.of parental lines were positive but the values altered with generation. Moreover, yield traits were detected with higher GCA and fiber traits with lower. Previous researches in F1and F2hybrids stated similar statistics for combining ability in upland cotton (Tang et al.1993; Khan et al. 2009). Among all inbred parental lines used in this study, P4 and P7 had the best GCA for multiple traits in F1and F2generations, and in both cotton belts (Table 4). These inbred lines’ superior performance in multiple traits, generations, and environments proposed their utilization in the further breeding program to develop elite hybrids. Interestingly.our results showed that the GC.of P4 was improved for LFFB, FBN, LY, BW, LP, and MIC in F2as compared with F1in both environments. The abrupt increase may be the resul.of heterogeneous material with different effects in F2which probably lead to good adaptation in different environments. The estimat.of heritability defines the rang.of genotypic and phenotypic variances. Therefore, it reveals the potentia.of parents to be selected and exploited to develop high-yielding genotypes. High heritability and GCA increased the probabilit.of selecting hybri.offspring with good performance in early generations (Sun et al.1994; Jia et al. 2017). Our results displayed that the majorit.of yield traits had strong H2and h2among different generations and environments (Tables 2 an.3). The traits with high heritability indexes showed are less vulnerable to diverse environments. Thus, simple selection in early generations would be an effective strategy to improve these traits (Soomro et al. 2010). In cotton breeding, GCA and heritability analysis provide a foundation to screen highly dominant materials (Li et al. 2010a). However, combined performance across multiple generations and ecological zones could be an efficient method to identify elite breeding populations.

Estimate.of SCA reflect the average performanc.of a hybrid combination and are mainly produced by the actio.of dominan.or epistatic gene interaction. This non-additive gene action mediates the mechanis.of heterosis in upland cotton (Ahuja and Dhayal 2007; Shahzad et al. 2020). Thus, estimate.of SCA provide a.opportunity to screen potential hybrid combinations in a particular generatio.or environment (Soomro et al. 2012; Khan et al. 2015). Our study revealed that the magnitud.of SCA varied with the traits, generations, and environments. Interestingly, combinations 9 and 2 had shown positive SCA effects in multiple traits in both F1and F2generation in two cotton belts, but for combinatio.3 an.15 in the two environments, the SC.of F1and F2showe.opposite results in multiple traits related to yield, quality, and agronomic traits. This is consistent with previous studie.on cotton F1hybrid combination with strong performance, and the dominance in F2was not necessarily well (Shang et al. 2012) (Tables 5 and6). In particular, yield and yield components were identified with higher SCA effects in these hybrids. Such promising results proposed that superior combinations may be utilized as F2hybrids to increase yiel.or as an elite population in advance breeding experiments. Besides this, those F2hybrid combinations with superior performance in a specific cotton belt would most likely be utilized to improve cotton productivity in such zone. Previous research stated that GCA and SCA were independent and higher GCA does not essentially interlink with higher SCA. Therefore, more emphasises should b.on SCA effects rather than the GCA effect.of inbred parents during the proces.of hybrid selection (Yang et al. 2009; Peng et al. 2015; Canavar et al. 2011). Correlation between traits plays a vital role in plant material selection (Liu et al. 2008). Our results showed a negative correlation between yield and quality characters in both cotton belts (Fig. 2). These results were consistent with those previously reported by different researchers (He et al. 2009; Li et al. 2010b). These results enabled improvement in yield-related traits independen.of fiber quality traits. Moreover, some agronomic traits showed a significant positive correlation with yield and quality traits in this study. Therefore, these agronomic traits should also be taken into consideration in the breedin.of hybrids across mechanical harvest cotton zones. Apart from this, how to improve fiber quality is still an important research topic in hybrid cotton breeding.

The utilizatio.of heterosis improved the productivit.of crops. Utilizatio.of heterosis i.on.of the key ways to improve stagnant yield in upland cotton. However, the major challenge is the difficult.of producing F1seed through manual emasculation and pollination (Wu et al. 2004) which caused the high cos.of production and seed impurity. To mitigate this challenge, the commercial us.of F2hybrids is proposed by many researchers (Li et al. 2000; Iqbal et al. 2015). The upland cotton belongs to allotetraploid, its F2segregation is not severe as in diploid rice and maize (Chen et al. 2020). Additionally, cotton has a long harvest period, and the plant architecture, growth stages, and agronomic traits may not have a direct impac.on the yield and fiber qualit.of F2generations (Wang et al. 2011; Kong et al. 2017). These unique cotton characteristics provide a.opportunity for the utilizatio.of F2hybrids to improve productivity. In this study, some combination.of F2hybrid generation performed well in multiple traits. For instance, combination 9 had shown excellent performance in multiple traits in both cotton belts (Fig.1; Additional fil.1). It illustrated that combinations with strong vigor performed well in F2(Liu et al. 2007; Zhang et al. 2018). Moreover, heterogeneity in F2most like enabled wider environment adaptation as compared with F1and inbred parents. Commercializatio.of elite F2hybrids no.only reduced production costs but also increased yields and promotes hybrid cotton.

In this study, we systematically evaluated the potential breeding application.of F2hybrids by comprehensive comparative analysi.of their field performanc.on yield, quality, and plant architecture-related traits. The combining ability variance and heritabilit.of traits significantly differed across multiple traits in two generations and both environments, suggesting that it is meaningful to select and breed hybrid F2generations in upland cotton. The GC.of parents P4 (L28) and P7 (Z98), and the F1and F2generation.of hybrid combination ZB × DT and combination L28 × Z98 in both environments were al.outstanding in many traits such as yield, quality, and plant architecture. Therefore, it is feasible to breed cotton F2with potential for production and application by synthetically evaluating the yield, quality, plant architecture traits, and environmental adaptabilit.of hybrid cotton F2through strict parent selection and in multi-plot experiments for several years.

Th.online version contains supplementary material available at https://doi.org/10.1186/s42397-022-00125-8.

Additional fil.1.Leve.of heterosis altered with the trait, hybrid combination, and generation in Anyang and Aral.

Additional file 2.Detail.of the top eight hybrid combinations in BPH, CH, and MPH for each trait in different generations and cotton belts.

Acknowledgements

We would like to thank the anonymous reviewers for their valuable comments and helpful suggestions which help to improve the manuscript.

Author contributions

Chen LL conducted the mos.of experiments and data analysis and drafted the manuscript. Tang HN, Zhang XX, Qi TX, Guo LP, Wang HL, Qiao XQ, and Zang R participated in data collection and performed par.of the statistical analysis. Zhang M and Shahzad K helped polish the language and revise the manuscript. Xing CZ, Wu JY, and Zhang M conceived, designed, and funded the study. All authors have read and approved the final manuscript.

Funding

This research was sponsored by funds from the Zhongyuan Academician Foundation (212101510001), the Fundamental Research Funds for State Key Laborator.of Cotton Biology (CB2021C08), and the General Progra.of the National Natural Science Foundatio.of China (31871679).