Heritability and predicted gain from selection in components of crop duration in divergent chickpea cross populations

Genetic analysis of ten quantitative traits related to crop duration in chickpea was carried out using three F ₂ sib-populations; 272-2 × CDC Anna, 298T-9 × CDC Anna and 298T-9 × CDC Frontier. F ₃ and F ₄ families from these populations were further evaluated for traits found important in the initial study. Also, 112 recombinant inbred lines (RILs) of chickpea cross ICCV 2 × JG 62 were evaluated for days to flowering, days to maturity and reproductive period. An analysis of the F ₂ population data using the mixed model approach revealed that the additive component of variance was significant for days to flowering, days to first podding and days to first pod maturity, while dominance genetic variance was significant for morphological components of crop duration such as height to first pod and height at flowering. Comparatively high heritability estimates (39–48%) were obtained for days to flowering, days to first pod maturity, percent pod maturity at four months after planting and days to maturity based on offspring-parent (F ₄ and F ₃ generations) regression and/or analysis of variance for the RIL population. The predicted gain from selection as a percentage of the population mean was low (5% or less) for these key components of crop duration owing to the low variability detected within the populations, the exception being percent pod maturity. To maximize gain from selection in these traits, it is therefore, essential to increase genetic variability among the progenies, potentially through multi-parent crosses that may involve gene introgression from across desi and kabuli types of chickpea and from wild progenitors.     

Commonality analysis and selection of parents for within-boll yield components in upland cotton

Relationships between lint yield and within-boll yield components are important for genetic improvement of lint yield in cotton (Gossypium hirsutum L.) cultivars. F₂ plants derived from crosses between germplasm lines and high yielding cultivars were analyzed to determine the contributions of within-boll yield components to lint yield and to select parents with desirable combining ability for multiple within-boll yield components. Forty-five F₂ hybrids were planted at two field sites in 2010 and 2011 with 4 and 3 replicates, respectively. There were a total of six yield components analyzed including lint percentage (LP), seed number per boll, lint weight per seed (LW_S), seed surface area per seed, lint weight per unit seed surface area (LW_SA), and lint number per unit seed surface area (LN_SA). The contributions of these yield components to lint yield were analyzed by commonality analysis that separated the contributions to lint yield into the unique contributions of single yield components and the common contributions of the single yield components with one or more other yield components. The unique contributions of the six yield components to lint yield ranged from 1.6 to 21 % of total variation for lint yield in the 2-year experiments. The greatest common contributions to lint yield among all combinations of the six yield components were identified for a combination of four components, LP, LW_S, LW_SA, and LN_SA with 67 and 44 % of the total variation of lint yield in 2010 and 2011, respectively. Results suggest that all four of these yield components should be considered simultaneously in breeding for genetic improvement of lint yield. The germplasm line SP225 was detected as a good combiner with positive general combining ability (GCA) for LP (1.4 %), LW_SA (0.03 mg mm^?2), and LN_SA (14.3 no mm^?2), and favorable GCA for fineness (?3.1 mg km^?1).     

Association mapping for seed cotton yield,yield components and fibre quality traits in upland cotton (Gossypium hirsutum L.) genotypes

Association mapping has revolutionized human genetics and is increasingly used in plant genetics. It is an efficient way of determining the genetic basis of complex traits. In cotton so far numerous association mapping studies are available as compared to many other important crops. In our study, mapping was performed using cotton 63K infinium beadchip with 201 germplasm lines. Through fast STRUCTURE analysis, lines were grouped into 12 subgroups and revealed genome sharing among the groups. The critical value (R²) was set to 0.243 as threshold to claim LD between two loci. About 3.13% marker pairs recorded significantly high LD (R² = 1), and 8.19% of marker pairs were in the range of 0.3 to 0.99 R². In MLM, 349 significant marker–trait associations were detected as against 642 in GLM because of effectiveness in eliminating false associations in MLM. A total of 68 markers explained >10% phenotypic variation for yield and fibre quality traits. Phenotypic variation explained by markers was smaller, suggesting that they might be associated with minor QTLs.     

Genome-wide association study of yield components and fibre quality traits in a cotton germplasm diversity panel

A genome-wide association study (GWAS) was conducted on a diversity panel of 103 cotton accessions over three seasons to determine genetic contributions to a range of cotton yield components including fibre quality, plant architecture and stomatal conductance traits. The accessions covered breeding lines, released cultivars and some obsolete cultivars that contributed significantly to modern breeding pools. They were genotyped with Illumina’s CottonSNP63 K single nucleotide polymorphism (SNP) assay. Broad-sense heritability was low for yield component traits (\(h_{B}^{2}\) = 0.14–0.43), except for gin turnout and boll weight (\(h_{B}^{2}\)) = 0.74 and 0.59, respectively), and low to high for fibre quality traits (\(h_{B}^{2}\) = 0.26–0.89). Population structure analysis revealed extensive admixture and cryptic relatedness amongst the accessions. Genome-wide linkage disequilibrium (LD) analyses showed LD decayed, on average, within a physical distance of 5 Mbp and reduced to 2 Mbp at r ² ≥ 0.2, suggesting that few markers are necessary for association mapping in cotton. A mixed linear model accounting for population structure and cryptic relatedness identified 17 and 50 significant SNP associations for fibre length and micronaire, respectively. GWAS failed to detect significant associations in other traits, with the contribution of any single SNP to the phenotypic falling below 5%. This may be due to the low level of DNA polymorphism in cotton and/or insufficient resolution provided by the cotton SNP chip. Whole genome sequencing combined with whole genomic selection approaches that do not require prior knowledge about the effect or function of individual SNPs may be better suited than GWAS for trait dissection and prediction in cotton breeding.     

Association analysis of yield and fibre quality characters in interspecific population of cotton (Gossypium spp.)

Seed cotton yield and fibre quality are controlled by polygenes and highly influenced by the environment. Hence, selection merely based on yield is not effective. In order to enhance the yield potential of the cotton varieties, an understanding of the relationship among different characters is of more importance. Knowledge on the direct contribution of different characters to yield would be highly important for formulating a selection programme. Correlation and path coefficient analysis were carried out using 62 progenies of an interspecific backcross population (Gossypium hirsutum L. var. KC 3 x Gossypium barbadense L. var. Suvin) x KC 3. Genotypic correlation studies revealed that number of bolls per plant, boll weight, number of sympodia per plant, number of seeds per boll, seed index, lint index, days to first flowering, and plant height have a significant positive association with seed cotton yield per plant. Path coefficient analysis showed that number of bolls per plant contributed maximum direct effect to seed cotton yield per plant followed by boll weight and lint index. The highest positive indirect effect on seed cotton yield per plant was also observed through number of bolls per plant. This indicated that seed cotton yield per plant was highly influenced by number of bolls per plant directly and indirectly. Thus, a greater emphasis should be given to number of bolls per plant, boll weight, and lint index for increasing seed cotton yield per plant.     

Breeding for high yield and fibre quality in coloured cotton

In the present study, three types of coloured fibre cottons, i.e. white, brown and green, were compared for their fibre quality and yield. The comparison of fibre quality suggested that coloured fibre cotton was inferior as compared with white fibre cotton. To understand the effect of cellulose, mineral elements [nitrogen (N), phosphorus (P) and potassium (K)] and pH of fibre cells on the quality of fibre, these components were studied at different fibre cell developed stages in all three fibre cotton types. The cellulose content is closely associated with the quality of fibre. The higher fibre quality of white fibre cotton might be the result of the high cellulose content in it compared with coloured fibre cotton. A rapid and slow decrease in pH in white and coloured cottons, respectively, might have some effects on fibre elongation. Among the mineral contents, potassium is positively correlated with the fibre quality traits. The pigment development patterns in brown and green fibre cottons are not similar. In green fibre cotton it takes more time to deepen in colour as compared with brown fibre cotton. Possible strategies for the improvement in quality of coloured fibre cotton are discussed. The results of heterosis studies in coloured fibre cotton suggest that heterosis could improve yield and quality of coloured fibre cotton. In the present study, the hybrids between ZJU12A x ZJU05R and ZJU18A x ZJU01R, having an acceptable lint colour types plus better fibre quality and high yield performance, may be exploited further for their heterotic advantages.     

Diallel analysis of yield components,fibre quality and bacterial blight resistance using spaced plants of cotton

Summary Hayman analysis for lint percentage, boll weight, fibre quality and bacterial blight resistance of a ten-parent half-diallel set of crosses was conducted in Upland cotton. The ten parents represented a fixed sample of the best germplasm available to Australian breeders for the characters of commercial importance. Heterosis and inbreeding depression were detected particulady for boll weight and blight resistance. An analysis of genetic components and parameters indicated that since additive effects were substantial and heritability high, early-generation selection of spaced plants and pure-line breeding should be successful. Some genotypes were identified as being potentially good donors for hybridization since they possessed dominant genes for improved character expression. Acala C-1 was identified as the first-choice parent for increased boll size. Coker 315 for increased span length, while Namcala was the best parent for breeding improved fibre strength. McNair 220 possessed the most dominant genes for high lint percentage. Reba P279 and Siokra were the only parents with resistance to the prevelant race of bacterial blight.     

Genetic association of within‐boll yield components and boll morphological traits with fibre properties in upland cotton (Gossypium hirsutum L.)

Knowledge of genetic relationships between within‐boll yield components and fibre quality is essential for simultaneous improvement of lint yield and fibre quality in upland cotton (Gossypium hirsutum L.). Nine parents and their F₁ progeny with reciprocals from a 3 × 6 factorial mating design were grown in 2008 and 2009. Seven within‐boll yield components and two boll morphological traits and the three fibre quality parameters were analysed based on a conditional additive/dominance (AD) genetic model. Results showed that boll length contributed to the largest proportion of phenotypic, additive and dominance variances for UHM length; seed index contributed to the largest proportion of phenotypic and additive variances for fibre strength; boll width made the largest contribution to phenotypic and additive variances and the second largest contribution to dominance‐by‐environment interaction variance for micronaire, indicating that they played an important role than the other traits for fibre length, strength and fineness/maturity, respectively. It is worthy of note that those correlations between boll shape and fibre quality apply only to the nine parents and the resultant hybrids in this study and do not imply a cause and effect relationship.     

Combining ability for yield and fibre characteristics in Tanzanian cotton germplasm

In Tanzania, cotton is of great economical importance, representing a large percentage of agricultural exports, but yield and lint quality is still relatively poor. The aim of this study was to identify parents to improve boll and lint yield and quality. Parents and F1 progeny of a 7 × 7 diallel were evaluated in four different environments. Results indicated significant variation for especially yield components, yield, ginning outturn and fibre quality. Parents with high and positive GCA like NTA 93-21, Delcot 344, Auburn 56 and MZ561 and combinations with high and positive SCA for the characteristics were identified. Additive genetic effects were seen for most of the characteristics, except for fibre strength at one locality. Parents with high GCA effects for certain characteristics produced combinations with high SCA effects for the same characteristics. This study indicated that there is enough genetic variability for boll and lint yield and quality for effective selection, and good parents that can be included in the breeding programme.     

Genetic mapping of quantitative trait loci for fiber quality and yield trait by RIL approach in Upland cotton

The improvement of cotton fiber quality has become more important because of changes in spinning technology. Stable quantitative trait loci (QTLs) for fiber quality will enable molecular marker-assisted selection to improve fiber quality of future cotton cultivars. A simple sequence repeat (SSR) genetic linkage map consisting of 156 loci covering 1,024.4 cM was constructed using a series of recombinant inbred lines (RIL) developed from an F₂ population of an Upland cotton (Gossypium hirsutum L.) cross 7235 × TM-1. Phenotypic data were collected at Nanjing and Guanyun County in 2002 and 2003 for 5 fiber quality and 6 yield traits. We found 25 major QTLs (LOD ≥ 3.0) and 28 putative QTLs (2.0 < LOD < 3.0) for fiber quality and yield components in two or four environments independently. Among the 25 QTLs with LOD ≥ 3, we found 4 QTLs with large effects on fiber quality and 7 QTLs with large effects on yield components. The most important chromosome D8 in the present study was densely populated with markers and QTLs, in which 36 SSR loci within a chromosomal region of 72.7 cM and 9 QTLs for 8 traits were detected.     

Recurrent selection progress in a population derived from an interspecific peanut cross

Summary Two cycles of recurrent selection for yield were previously conducted using a population of Arachis hypogaea L.-like tetraploid hybrid derivatives selected from among the progeny of a cross between A. hypogaea and A. cardenasii Krap. et Greg. nom. nud., a diploid species with resistance to late leafspot (Cercosporidium personatum (Burk. and Curt.) Deighton). Using the 10 highest yielding parents from each of the above cycles of recurrent selection, a study was conducted for 12 morphological traits and susceptibility to leafspot infection in a replicated test at a single location. The two parents used to initiate the interspecific hybrid population (PI 261942-3 and A. cardenasii) as well as two adapted cultivars (Florigiant and NC 7) were included as checks. The objectives of the study were to determine the amount of genetic variation remaining in the population after two cycles of recurrent selection in order to predict whether further progress from selection could be expected and determine the potential for utilizing wild species for the improvement of quantitative traits in peanut. The results indicate that significant levels of genetic variation remain in the population after two cycles of recurrent selection for all traits measured, including several components of yield and leafspot resistance. This suggests that continued progress in population improvement from further cycles of selection should be possible while enhancing the genetic diversity of cultivated peanut germplasm.Paper no. 12347 of the Journal Series of the North Carolina Agric. Res. Serv., Raleigh, NC 27695-7643. This work was partially funded by the Peanut CRSP, USAID grant number DAN-4048-G-SS-2065-00. Recommendations do not represent an official position or policy of USAID.     

Quantitative trait loci mapping for yield components and kernel-related traits in multiple connected RIL populations in maize

Grain yield is one of the most important and complex quantitative traits in maize breeding. In the present study, a total of 11 connected RIL populations, derived from crosses between elite inbreed “Huangzaosi” as the common parent and 11 elite inbreeds, were evaluated for five yield components and kernel-related traits under six environments. Quantitative trait loci (QTL) were detected for the traits under each environment and in joint analysis across all environments for each population. A total of 146 major QTL with R² > 10 % in at least one environment and also detected based on joint analysis across all environments were identified in the 11 populations. Lqkwei4 conferring kernel weight and Lqklen4-1 conferring kernel length both located in the adjacent marker intervals in bin 4.05 were stably expressed in four environments and in joint analysis across six environments, with the largest R² over 27 and 24 % in a single environment, respectively. Moreover, all major QTL detected in the 11 populations were aligned on the IBM2 2008 neighbors reference map. Totally 16 common QTL (CQTL) were detected. Seven important CQTL (CQTL1-2, CQTL1-3, CQTL4-1, CQTL4-2, CQTL4-3, CQTL4-4, and CQTL6-1) were located in bin 1.07, 1.10, 4.03, 4.05, 4.08, 4.09 and 6.01–6.02, respectively. These chromosomal regions could be targets for fine mapping and marker-assisted selection.     

Genome mapping and molecular markers identification for yield,yield component and fibre quality traits in tetraploid cotton

The identification of quantitative trait loci (QTL) across different environments is a prerequisite for marker‐assisted selection (MAS) in crop improvement programmes. CottonSNP63k Illumina infinium array was used for genotyping 178 inter‐specific recombinant inbred lines and the parents, and identified 1,667 homozygous polymorphic markers between the parents. Of these, 1,430 markers were used for the construction of linkage map after removing 237 redundant markers. The genetic map spans a total genetic length of 3,149.8 cM with an average marker interval size of 2.2 cM. The phenotypic data from five environments were analysed separately using inclusive composite interval mapping which identified a total of 56 QTL explaining phenotypic variances (PVE) in the range of 8.18%–28.91%. There were 11 and 24 major QTL found for fibre quality and yield components, respectively. A total of 64 QTL were identified through Multi‐Environment Trials analysis, of which 34 recorded QTL × Environment interactions.     

Simultaneous selection for yield-related traits and susceptibility to Fusarium head blight in spring wheat RIL population

Fusarium head blight (FHB), caused by the fungal plant pathogen Fusarium, is a fungal disease that occurs in wheat and can cause significant yield and grain quality losses. The present paper examines variation in the resistance of spring wheat lines derived from a cross between Zebra and Saar cultivars. Experiments covering 198 lines and parental cultivars were conducted in three years, in which inoculation with Fusarium culmorum was applied. Resistance levels were estimated by scoring disease symptoms on kernels. In spite of a similar reaction of parents to F. culmorum infection, significant differentiation between lines was found in all the analyzed traits. Seven molecular markers selected as linked to FHB resistance QTLs gave polymorphic products for Zebra and Saar: Xgwm566, Xgwm46, Xgwm389, Xgwm533, Xgwm156, Xwmc238, and Xgwm341. Markers Xgwm389 and Xgwm533 were associated with the rate of Fusarium-damaged kernels (FDK) as well as with kernel weight per spike and thousand kernel weight in control plants. Zebra allele of marker Xwmc238 increased kernel weight per spike and thousand kernel weight both in control and infected plants, whereas Zebra allele of marker Xgwm566 reduced the percentage of FDK and simultaneously reduced the thousand kernel weight in control and infected plants.     

Density responses and spatial distribution of cotton yield and yield components in jujube (Zizyphus jujube)/cotton (Gossypium hirsutum) agroforestry

Trees are the dominant species in agroforestry systems, profoundly affecting the performance of understory crops. Proximity to trees is a key factor in crop performance, but rather little information is available on the spatial distribution of yield and yield components of crop species under the influence of trees in agroforestry systems. Also, little information is available on how crop density may be exploited to optimize the yield in such systems. Here we studied the performance of cotton in jujube/cotton agroforestry. Field experiments were conducted in 2012 and 2013 in Hetian, Xinjiang, China. Cotton was grown at a row distance of 60 cm in three densities, 13.5, 18.0 and 22.5 plants m⁻² in six m wide paths between tree lines in a jujube plantation. Plant density affected both cotton aboveground dry matter and yield significantly. The highest yield was attained at the intermediate density of 18.0 plants m⁻² (20.0 plants m⁻² corresponding in sole cotton), lower than the optimal density in sole cotton (25.0 plants m⁻²). Yield at the lower density was constrained by the low number of bolls per m² as a direct consequence of the low density, whereas at the high plant density yield was constrained by a lower allocation of assimilates to cotton seed and lint, as a consequence of intraspecific and interspecific competitions. There were strong gradients in yield and yield components in relation to the distance from the tree rows. Leaf area and total dry matter of cotton in rows close to the tree lines were reduced, especially in the rows next to the trees. Moreover, biomass allocation to cotton fruits was reduced in these rows. Competitive influences from the trees on cotton performance extended two rows deep in a six-year old jujube stand, and even three rows deep in a seven-year old stand. Shading effects on cotton yield were compensated by increasing plant density as a result of greater boll numbers per unit ground area. Data from this study help guide the design of optimal plant density of cotton in jujube plantations and give insight in the spatial distribution and dynamics of competitive effects in agroforestry systems in general.     

Germplasm for genetic improvement of lint yield in Upland cotton: genetic analysis of lint yield with yield components

Determination of genetic effects for lint yield and yield components in cotton (Gossypium hirsutum L.) germplasm is critical for its utilization in breeding programs. This study was designed to apply the conditional approach and an additive and dominant model to analyze genetic effects for lint yield and yield components. Forty-eight F₂ populations derived from crosses between four existent Upland cotton cultivars as female parents and 12 germplasm lines as male parents were evaluated at two locations in 2008 and 2009. Conditional and unconditional variance components were estimated by the mixed linear model based conditional approach. Lint yield and yield components were mainly controlled by genotypic effects, i.e., additive variance and dominance variance (≥66 % of total phenotypic variation). Lint percentage and lint index had the highest proportions of additive variance component to the total phenotypic variances. SP156 and SP205 had positive additive effects for lint yield and yield components, and were also parents of the most hybrids with positive predicted dominant effects. Therefore, these two lines are good combiners for development of both pure lines and hybrids. Positive additive contribution effects to lint yield from lint percentage, boll number, boll weight, and seed index were detected in different parents. Adding seed index to boll number and lint percentage increased additive contribution effects to lint yield from these two components relative to the contribution effects from either boll number or lint percentage alone. Results in this study suggest that boll number, lint percentage, and seed index should be balanced in pure line development.     

Quantitative trait loci and candidate genes for yield and related traits in Madhukar x Swarna RIL population of rice

Yield of popular rice varieties such as Swarna grown in rainfed lowlands and Madhukar grown in flood prone areas needs to be continuously improved. Recombinant inbred lines (RILs) were developed from the cross between two indica cultivars Madhukar and Swarna. QTLs were mapped using 110 markers in 168 RILs. In all, 26 QTLs were mapped for yield and five related traits on chromosomes 1, 2, 3, 6, 7, 8, 10, 11, and 12. QTL for plant height and days to flowering were co-located between RM23147 — RM337 on chromosome 8. RM251, RM314, and RM1135 were significantly associated with plant height and OsYSL17 was significantly linked with grain yield. Epistatic interaction was detected for plant height and number of tillers. Several candidate genes reported for yield and related traits underlie the QTL regions.     

常规棉与杂交棉产量构成因素的偏相关和通径分析

采用偏相关和通径分析方法,对2004年河南省常规棉和杂交棉区试资料的皮棉产量及其构成因素进行分析.结果表明,皮棉产量构成因素中,无论常规棉和杂交棉,单株结铃数受环境影响最大;对常规棉,单株铃数对皮棉产量作用最大,其次分别是单铃重、衣分;对杂交棉,衣分对皮棉产量作用最大,其次分别是单株铃数、单铃重.据此结果提出常规棉和杂交棉品种选育策略和栽培的主攻方向.     

Heritability estimates and response to selection for the pungency and single center traits in onion

Summary Heritabilities of the pungency and single center traits were estimated in onion breeding populations using selection response and half-sib family analyses. Pungency was determined indirectly by measuring enzymatically produced pyruvic acid in individual bulbs. After one generation of selection, pungency was lowered by 8.1% and 8.9% in the populations 90-61-1 and 89-69-8, respectively, and realized heritabilities of 0.21 and 0.51 were estimated.Selection had no effect in lowering the pungency of population 90–62. Heritability estimates calculated through half-sib progeny analysis were 0.53, 0.48, and 0.25 for pungency in the populations 90-61-1, 90–62 and 89-69-8, respectively. The number of single centered onions was increased by 19% and 22% in populations 90–62 and 89-69-8, respectively, after one generation of selection, and the realized heritability estimates were 0.37 and 0.34, respectively.