Background: Heterosis has been extensively utilized in different crops and made a significant contribution to global food security. Genetic distance (GD) is one of the valuable criteria for selecting parents in hybrid breeding. The objectives of this study were to estimate the GD between parents using both simple sequence repeat (SSR) markers and single nucleotide polymorphism (SNP) markers and to investigate the efficiency of the prediction of hybrid performance based on GD. The experiment comprised of four male parents, 282 female parents and 1128 F1, derived from NCII mating scheme. The hybrids, their parents with two check cultivars were evaluated for two years. Performance of F1, mid-parent heterosis (MPH), and best parent heterosis (BPH) were evaluated for ten agronomic and fiber quality traits. Results: Heterosis was observed in all hybrids and, the traits like plant height, boll number, boll weight and lint percentage exhibited higher heterosis than the fiber quality traits. Correlations were significant between parental and F1 performances. The F­1 performances between three hybrid sets (Elite×Elite, Exotic×Elite, and Historic×Elite) showed significant differences in eight traits. The correlation of the GD assessed by both SSR and SNP markers was significantly positive. The cluster analysis based on GD results estimated using SNP showed that all the female parents divided into five groups and the F1 performance between these five groups showed significant differences in seven traits. The correlation between GD and F1 performance, MPH and BPH were significant for lint percentage and micronaire. Conclusions: Our results suggested that GD between parents could be helpful in heterosis prediction for certain traits. This study reveals that molecular marker analysis can serve as a basis for assigning germplasm into heterotic groups and to provide guidelines for parental selection in hybrid cotton breeding.

Background: Upland cotton (Gossypium hirsutum) accounts for more than 90% of annual world cotton output due to its high yield potential. However, yield traits and fiber quality traits exhibit negative correlations in most cases. Here, to dissect simultaneously the genetic basis underlying complex traits such as yield and fiber quality as well as their genetic correlations in upland cotton, four F2 populations were constructed using two normal lines and two introgression lines. Subsequently, phenotyping of 8 agronomic and economic traits along with QTL mapping were implemented.Results: Extensive phenotype variations and transgressive segregation were found across segregation populations. Four genetic maps with length of 585.97cM, 752.45cM, 752.45cM and 1163.66cM were construct. The result of mapping displayed a total of 50 QTLs across four populations were identified, of which 27 were for fiber quality traits and 16 for yield traits. Multiple QTLs having the common maker, such as qBW4 and qBW2, or residing in the same QTL cluster, such as qLP9 and qFL9-1, were prioritized for further research.Conclusions: These findings will provide insight into simultaneous improvement of yield and fiber quality in upland cotton breeding.

Background Stem hardness is one of the major influencing factors for plant architecture in upland cotton (Gossypium hirsutum L.). Evaluating hardness phenotypic traits is very important for the selection elite lines for resistant to lodging in Gossypium hirsutum L. Cotton breeder are interested in using diverse genotypes to enhance fibre quality and high- yield. The research for hardness and its relation with fiber quality and yield were very few. This study was designed to find the relationship of stem hardness traits with fiber quality and yield contributing traits of upland cotton. Results Experiments were carried out to measure the bending, acupuncture and compression properties of stem from a collection of upland cotton genotypes, comprising 237 accessions. The results showed that the genotypic difference in stem hardness were highly significant among the genotypes, and the stem hardness traits (BL, BU, AL, AU, CL and CU) have a positive association with fiber quality traits and yield related traits. In descriptive statistics result bending (BL, BU) have maximum coefficient of variance and trait fiber length and fiber strength have less coefficient of variance among the genotypes. Principal component analysis (PCA) reduced quantitative characters into nine principal components. The first nine principal components (PC) with Eigen values >1 explained 0.86% of variation among 237 accessions of cotton crop. Both 2017& 2018, PCA results indicated that BL, BU, FL, FE and LI variables contributed their variability in PC1 and BU, AU, CU, FD, LP and FWPB have shown their variability in PC2. Conclusion We describe here, to the best of our knowledge, the systematic study of the mechanism involved in the regulation of enhancing fiber quality and yield by stem bending strength, acupuncture and compression properties of Gossypium hirsutum crop.

Background: Heterosis has been extensively utilized in different crops and made a significant contribution to global food security. Genetic distance (GD) is one of the valuable criteria for selecting parents in hybrid breeding. The objectives of this study were to estimate the GD between parents using both simple sequence repeat (SSR) markers and single nucleotide polymorphism (SNP) markers and to investigate the efficiency of the prediction of hybrid performance based on GD. The experiment comprised of four male parents, 282 female parents and 1128 F1, derived from NCII mating scheme. The hybrids, their parents and two check cultivars were evaluated for two years. Performance of F1, mid-parent heterosis (MPH), and best parent heterosis (BPH) were evaluated for ten agronomic and fiber quality traits, including plant height, boll weight, boll number, lint percentage, fiber length, fiber strength, fiber uniformity, fiber elongation ratio, micronaire, and spinning consistent index. Results: Heterosis was observed in all hybrids and, the traits like plant height, boll number, boll weight and lint percentage exhibited higher heterosis than the fiber quality traits. Correlations were significant between parental and F1 performances. The F­1 performances between three hybrid sets (Elite×Elite, Exotic×Elite, and Historic×Elite) showed significant differences in eight traits, including boll number, lint percentage, fiber length, fiber strength, fiber uniformity, fiber elongation ratio, micronaire, and spinning consistent index. The correlation of the GD assessed by both SSR and SNP markers was significantly positive. The cluster analysis based on GD results estimated using SNP showed that all the female parents divided into five groups and the F1 performance between these five groups showed significant differences in four traits, including lint percentage, micronaire, fiber strength, and fiber elongation ratio. The correlation between GD and F1 performance, MPH and BPH were significant for lint percentage and micronaire. Conclusions: Our results suggested that GD between parents could be helpful in heterosis prediction for certain traits. This study reveals that molecular marker analysis can serve as a basis for assigning germplasm into heterotic groups and to provide guidelines for parental selection in hybrid cotton breeding.

Background: Upland cotton (Gossypium hirsutum) accounts for more than 90% of the annual world cotton output because of its high yield potential. However, yield and fiber quality traits often show negative correlations. We constructed four F2 populations of unland cotton, using two normal lines (4133B and SGK9708) with high yield potential but moderate fiber quality and two introgression lines (Suyuan04-3 and J02-247) with superior fiber quality, and used them to investigate the genetic basis underlying complex traits such as yield and fiber quality in upland cotton. We also phenotyped eight agronomic and economic traits and mapped quantitative trait loci (QTLs). Results: Extensive phenotype variations and transgressive segregation were found across the segregation populations. We constructed four genetic maps of 585.97 cM, 752.45 cM, 752.45 cM and 1 163.66 cM, one for each of the four F2 populations.. Fifty QTLs were identified across the four populations (7 for plant height, 27 for fiber quality and 16 for yield). The same QTLs were identified in different populations, including qBW4 and qBW2, which were linked to a common simple sequence repeat (SSR) marker, NAU1255. A QTL cluster containing eight QTLs for six different traits was characterized on linkage group 9 of the 4133B×Suyuan04-3 population. Conclusions: These findings will provide insights into the genetic basis of simultaneous improvement of yield and fiber quality in upland cotton breeding.

Background: Upland cotton (Gossypium hirsutum) accounts for more than 90% of annual world cotton output due to its high yield potential. However, yield traits and fiber quality traits exhibit negative correlations in most cases. Here, we constructed four F2 populations, using two normal lines and two introgression lines, for simultaneously detection the genetic basis underlying complex traits such as yield and fiber quality in upland cotton. Subsequently, the phenotyping of 8 agronomic and economic traits along with quantitative trait loci (QTL) mapping was implemented. Results: Extensive phenotype variations and transgressive segregation were found across segregation populations. Four genetic maps were constructed with the length of 585.97cM, 752.45cM, 752.45cM and 1163.66cM. The mapping resulted in the identification 50 QTLs (27 were for fiber quality traits and 16 for yield traits) across four populations. Multiple QTLs having the common maker, such as qBW4 and qBW2, or residing in the same QTL cluster, such as qLP9 and qFL9-1, were prioritized for further research. Conclusions: These findings will provide insight into the genetic basis of simultaneous improvement of yield and fiber quality in upland cotton breeding.

Background Stem hardness is one of the major influencing factors for plant architecture in upland cotton (Gossypium hirsutum L.). Evaluating hardness phenotypic traits is very important for the selection of elite lines for resistance to lodging in Gossypium hirsutum L. Cotton breeder are interested in using diverse genotypes to enhance fiber quality and high-yield. The research for hardness and its relation with fiber quality and yield were very few. This study was designed to find the relationship of stem hardness traits with fiber quality and yield contributing traits of upland cotton. Results Experiments were carried out to measure the bending, acupuncture, and compression properties of the stem from a collection of upland cotton genotypes, comprising 237 accessions. The results showed that the genotypic difference in stem hardness was highly significant among the genotypes, and the stem hardness traits (BL, BU, AL, AU, CL, and CU) have a positive association with fiber quality traits and yield-related traits. Statistical analyses of the results showed that bending (BL, BU) has a maximum coefficient of variance and trait fiber length and fiber strength have less coefficient of variance among the genotypes. Principal component analysis (PCA) reduced quantitative characters into nine principal components. The first nine principal components (PC) with Eigenvalues >1 explained 86% of the variation among 237 accessions of the cotton crop. Both 2017& 2018, PCA results indicated that BL, BU, FL, FE, and LI variables contributed their variability in PC1 and BU, AU, CU, FD, LP, and FWPB have shown their variability in PC2. Conclusion We describe here, to the best of our knowledge, the systematic study of the mechanism involved in the regulation of enhancing fiber quality and yield by stem bending strength, acupuncture, and compression properties of Gossypium hirsutum crop.