Quantitative trait loci mapping of forage stover quality traits in six mapping populations derived from European elite maize germplasm

Four forage maize stover quality traits were analysed including in vitro digestibility of organic matter (IVDOM), neutral detergent fibre (NDF), water‐soluble carbohydrates (WSC) and digestibility of NDF (DNDF). We mapped quantitative trait loci (QTL) in three DH (doubled haploid) populations (totally 250–720 DH lines): one RIL population (358 lines) and two testcross (TC) populations, based on field phenotyping at multiple locations and years for each. High phenotypic and genotypic correlations were found for all traits and significant (p < .01) at two locations, and NDF was negatively correlated with the other traits. QTL analyses were conducted by composite interval mapping. A total of 33, 23, 32 and 25 QTL were identified for IVDOM, NDF, WSC and DNDF, respectively, with three, four, five and two major QTL for each. Few consistent QTL for IVDOM, WSC and DNDF were detected in more than two populations. This study contributed to the identification of key QTL associated with forage maize digestibility traits and is beneficial for marker‐assisted breeding and fine mapping of candidate genes associated with forage maize quality.     

QTL mapping of improving forage maize starch degradability in European elite maize germplasm

Improving maize starch content is of great importance for both forage and grain yield. In this study, 13 starch degradability traits were analysed including percentage of the seedling area, floury endosperm, hard endosperm of total grain area, percentage of the floury endosperm surface and vitreousness ratio surface hard: floury endosperm surface, etc. We mapped quantitative trait loci (QTL) in a biparental population of 309 doubled haploid lines based on field phenotyping at two locations. A genetic linkage map was constructed using 168 SSR (simple sequence repeat) markers, which covered 1508 cM of the maize genome, with an average distance of 9.0 cM. Close phenotypic and genotypic correlations were found for all traits, and were all statistically significant (p = 0.01) at two locations. Major QTL for more than two traits were detected, especially in two regions in bins 4.05–4.06 and 7.04–7.05, associated with 13 and 9 traits, respectively. This study contributes to marker‐assisted breeding and also to fine mapping candidate genes associated with maize starch degradability.     

Economic Aspects of Breeding for Yield and Quality Traits in Forage Maize

The economic evaluation of forage maize is complex due to its usage in different types of farms as well as the interdependencies of forage maize traits with the farm organization and the intensity of production. By means of linear programming, the economic weights of important forage maize traits were calculated for farming conditions in Germany. They were determined from the difference in the gross margins of farm models for given changes in a single trait of forage maize and were calculated for dairy and bull-fattening farms under five levels of animal performance, three stocking rates, and different levels of forage maize traits. Individual economic weights under these settings varied little in most cases and allowed aggregation of mean economic weights. They amounted to 4.6 ECU ha^?1 for metabolizable energy yield (GJ ha^?1), 207 ECU ha^?1 for metabolizable energy content (MJ kg^?1), and 3.1 ECU ha^?1 for crude protein content (g kg^?1). Economic weight for forage dry matter content was strongly dependent upon the maturity of the materials and varied between -5 and 25 ECU ha^?1. The application of economic weights was discussed in comparison with other criteria for the assessment of experimental hybrids in official trials.     

Genetic improvement of cell-wall digestibility in forage maize (Zea mays L.). I. Performance of inbred lines and related hybrids

Summary The current study deals with genetic improvement of the nutritive value of forage maize. In separate field trials, maize inbred lines without the brown midrib trait and derived hybrids were evaluated for stalk quality as well as some other agronomic traits. The aim was to relate the performance of lines and hybrids. Quality traits studied were the contents of ash and cell walls expressed as percentage of dry matter and the digestibilities of organic matter and cell walls (stalk-dv% and stalk-dcw%, respectively). The performance of hybrids was established in a trial at two locations with three replicates per location and the performance of lines at one location in an unreplicated trial.The range for stalk-dcw% was about 10 percentage units between hybrids and 15 percentage units between inbred lines. Stalk-dcw% had of all quality traits of hybrids the highest broad-sense heritability (h ²=0.74), and determined about 80% of the variation in stalk-dv%. The only stalk quality trait where a significant correlation was found between the mean hybrid performance and the corresponding midparent value was stalk-dcw% (r=0.70, P<0.01).In conclusion, stalk-dcw% proved to be the only stalk quality trait worth evaluating at the inbred line level in a breeding programme aimed at producing commercial hybrid varieties of forage maize.     

Differentiation of resistance genes at the M1-a locus in six pairs of isogenic barley lines

Summary Five pairs of lines, nearly isogenic except for genes for resistance and susceptibility to culture CR3 of Erysiphe graminis (DC). Merat hordei Em. Marchal, developed from the barley (Hordeum vulgare L.) varieties Algerian, Franger, Durani, Rupee, and Multan, had five different genes at the M1-a locus on chromosome 5 conditioning resistance to culture CR3. The resistant isogenic lines developed from Durani, Rupee, and Multan each had one additional resistance gene, closely linked in coupling to their resistance gene at the M1-a locus, conditioning resistance to culture 63.5 or 64.54. The sixth pair of isogenic lines, developed from the variety Long Glumes, had three resistance genes: one at the M1-a locus, a second closely linked in coupling to the first, and a third gene. The first and the third genes in Long Glumes appear to be the same as the two genes in Multan. The outstanding resistance to E. graminis hordei of most of the donor varieties for the isogenic lines is explained by their possessing two or more resistance genes. The presence of approximately 20 different genes in and around the M1-a locus suggests that there is a cluster of closely linked resistance loci in that region of chromosome 5.Contribution from Applied Plant Genetics Laboratory, Northeastern Region, Agricultural Research Service, U.S. Department of Agriculture, in cooperation with the Agricultural Research Department, Danish Atomic Energy Commission.     

Stay green trait: variation, inheritance and its association with spot blotch resistance in spring wheat (Triticum aestivum L.)

One thousand four hundred and seven spring wheat germplasm lines belonging to Indian and CIMMYT wheat programs were evaluated for stay green (SG) trait and resistance to spot blotch caused by Bipolaris sorokiniana during three consecutive crop seasons, 1999–2000, 2000–2001 and 2001–2002. Disease severity was recorded at six different growth stages beginning from tillering to late milk stage. SG trait was measured by following two approaches: difference for 0–9 scoring of green coloration (chlorophyll) of flag leaf and spike at the late dough stage (GS 87) and a new approach of leaf area under greenness (LAUG). Germplasm lines showed a wide range (7–89) for LAUG and were grouped into four viz., SG, moderately stay green, moderately non-stay green and non-stay green (NSG). However, very few (2.2%) lines showed high expression of SG trait, i.e., LAUG >60. LAUG appeared to be a better measure of SG trait than a 0–9 scale. Mean spot blotch ratings of SG genotypes were significantly lower than those of NSG genotypes at all growth stages. Two spot blotch resistant genotypes (Chirya 3 and Chirya 7) having strong expressions of SG trait were crossed with NSG, spot blotch susceptible cv. Sonalika. Individually threshed F₂ plants were used to advance the generations. SG trait and spot blotch severity were recorded in the parents and F₁, F₃, F₄, F₅, F₆ and F_6–7 generations under disease-protected and inoculated conditions. SG trait in the F₁ generation was intermediate and showed absence of dominance. Evaluation of progenies (202–207) in the segregating generations revealed that SG trait was under the control of around four additive genes. Lines homozygous for SG trait in F₄, F₅, F₆ and F_6–7 generations showed significantly lower mean area under disease progress curve (AUDPC) for spot blotch than those with NSG expression. A positive correlation (0.73) between SG trait and AUDPC further indicated a positive influence of SG on severity of spot blotch. The study established that variation for SG trait exists in spring wheat; around four additive genes control its inheritance in the crosses studied and there is positive association between SG trait and resistance to spot blotch.     

Anthocyanin mutations improving tomato and pepper tolerance to adverse climatic conditions

The effect of four mutated genes affecting anthocyanin biosynthesis was investigated relative to tomato and pepper germination capacities and early seedlings and plantlets growth. The study was performed on isogenic/near isogenic lines (IL/NIL) differing for genes ah (Hoffmann’s anthocyaninless), aw (anthocyanin without) and bls (babylea syndrome) in tomato and al ₁ (anthocyaninless – 1) in pepper. Germination responses of the IL/NILs showed that genes ah, aw and bls in tomato and al ₁ in pepper enhanced germination abilities under stress conditions regardless of the inherent seed properties that imparted rapid germination. This evaluation was conducted with four very different types of stress: 13 ^°C, 33 ^°C,120 mM NaCl and 15% PEG-6000 water solutions. The four genes exercised no effect on root and hypocotyl elongation under the same stress conditions and their effect on plantlets growth varied depending on the genotype and the treatment. The usefulness of genes ah, aw, blsand al ₁ in breeding tomato and pepper cultivars tolerant to adverse climatic conditions at germination when used as a morphological marker, is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Utilisation of <Emphasis Type="Italic">Aegilops</Emphasis> (goatgrass) species to widen the genetic diversity of cultivated wheat

Wild Aegilops species related to cultivated wheat (Triticum spp.) possess numerous genes of agronomic interest and can be valuable sources of resistance to diseases, pests and extreme environmental factors. These genes can be incorporated into the wheat genome via intergeneric crossing, following, where necessary, the development of chromosome addition and substitution lines from the resulting hybrids. The transfer of a single segment from an alien chromosome can be achieved by translocations. The Aegilops (goatgrass) species, which are the most closely related to wheat, exhibit great genetic diversity, the exploitation of which has been the subject of experimentation for more than a century. The present paper gives a survey of the results achieved to date in the field of wheat–Aegilops hybridisation and gene transfer. The Aegilops genus consists of 11 diploid, 10 tetraploid and 2 hexaploid species. Of these 23 Aegilops species, most of the diploids (Ae. umbellulata Zhuk., Ae. mutica Boiss., Ae. bicornis (Forssk.) Jaub. & Spach, Ae. searsii Feldman & Kislev ex Hammer, Ae. caudata L., Ae. sharonensis Eig, Ae. speltoides Tausch, Ae. longissima Schweinf. & Muschl.) and several polyploids (Ae. ventricosa Tausch, Ae. peregrina (Hack. In J. Fraser) Marie & Weiller, Ae. geniculata Roth, Ae. kotschyi Boiss., Ae. biuncialis L.) have been used to develop wheat–Aegilops addition lines. Wheat–Aegilops substitution lines were developed using several species, including Ae. umbellulata, Ae. caudata, Ae. tauschii, Ae. speltoides, Ae. sharonensis, Ae. longissima and Ae. geniculata. Translocations carrying genes responsible for useful agronomic traits were developed with Ae. umbellulata, Ae. comosa, Ae. ventricosa, Ae. longissima, Ae. speltoides and Ae. geniculata. A large number of genes were transferred from Aegilops species to cultivated wheat, including those for resistance to leaf rust, stem rust, yellow rust and powdery mildew, and various pests (cereal cyst nematode, root knot nematode, Hessian fly, greenbug). Many molecular markers are linked to these resistance genes. The development of new molecular markers is also underway. There are still many untapped genetic resources in Aegilops species that could be used as resistance sources for plant breeding.     

Identification of QTLs for phosphorus utilization efficiency in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) across P levels

It is necessary to develop maize plants that are productive when grown in phosphorus (P) deficient soils because of the high cost of P supplementation in soils. The shoot phosphorus utilization efficiency, the whole phosphorus utilization efficiency of plant and root/shoot ratio as well as the quantitative trait loci associated with these traits were determined for a F_2:3 population derived from the cross of two contrasting maize (Zea mays L.) genotypes, 082 and Ye107. A total of 241 F_2:3 families were evaluated in replicated trials under deficient and normal phosphorus conditions in 2007 at Southwest University. The genetic map constructed by 275 SSR and 146 AFLP markers spanned 1,681.3 cM in length with an average interval of 3.84 cM between adjacent markers. Phosphorus was determined in harvested plants separated into two portions, roots and shoots with leaves. The sum of the two portions was used as an expression for P in the whole plant. By using composite interval mapping, a total of 5–8 distinct QTLs were identified under deficient and normal phosphorus, respectively. SPUE and WPUE under deficient phosphorus were controlled by one QTL, which was in the interval bnlg1518-bnlg1526 (bins 10.04) on chromosome 10. The loci of QTLs were same for SPUE, WPUE and RSR under normal phosphorus, which were in the interval bnlg1518–bnlg1526 (bins 10.04) and P2M8/a-bnlg1839 (bins10.07) on chromosome 10. Unlike regions conferring phosphorus utilization efficiency and root shoot ratio under normal phosphorus, the region under deficient phosphorus showed that genes controlling phosphorus utilization efficiency or root shoot ratio might be different. These results may be useful to breeding programs in marker assisted selections to identify phosphorus tolerant genotypes. Junyi Chen and Li Xu contributed equally to this work.     

Screening global <Emphasis Type="Italic">Medicago</Emphasis> germplasm for weevil (<Emphasis Type="Italic">Hypera postica</Emphasis> Gyll.) tolerance and estimation of genetic variability using molecular markers

The genus Medicago encompasses many important forage species for both temperate and tropical regions. M. sativa L., commonly known as lucerne, is one of the most important forage species grown worldwide, but its production suffers seriously from weevil (Hypera postica Gyll.) infestation. The aim of this work was to identify species/accessions with tolerance to weevil and their molecular analysis using simple sequence repeat (SSR) markers. After screening 197 global germplasm encompassing 50 Medicago species for weevil tolerance, 22 lines representing 13 species were identified where leaf damage was ≤15% (P ≤ 0.05). In total, 37 accessions of the 22 lines, five Indian lucerne cultivars with leaf damage ≥75% and 10 accessions of the 13 Medicago species with low to high infestation (>25%) were molecularly assessed using 11 SSR markers (5 newly developed) to delineate closest to lucerne lines for breeding. In total, 33 bands were scored. The SAHN clustering using UPGM algorithm resulted into two main clusters supported with high boot strap values and with genetic similarity ranging from 0.33 to 0.96. Two accessions of M. tenoreana were observed closest to Indian lucerne cultivars. The rich variability revealed can be used as potential resource for transferring genes across species. Although the inter-specific hybridization is difficult preposition in genus Medicago largely due to post fertilization barrier, the identified species/accessions can be utilized on priority in breeding programs especially employing biotechnological tools like culturing of fertilized pods, ovule-embryo culture and electroporation.     

Regular segregation of four recessive marker genes among maternal haploids in maize

The objective of the study was to investigate whether a population of maternal haploid plants represents a random gametic array. Four inbred lines of maize (A619, MK01, 092 and 19‐3‐3) were used in the present study. These were crossed with line TO carrying four recessive genes: brown midrib (bm2), liguleless (Ig1), white endosperm (g1) and golden plant (g1). Maternal haploids were produced from the F ¹ hybrids, using a haploid‐inducing pollinator line. Segregation of haploids for the marker genes was estimated under field conditions. The observed segregation data agreed with the expected 1:1 ratio. It is concluded that no segregation distortion occurred during the production of maternal haploids.     

Pyramiding of thermosensitive genetic male sterility (TGMS) genes and identification of a candidate tms5 gene in rice

Three thermosensitive genetic male sterility (TGMS) genes – tms2, tgms and tms5 – were pyramided using linked microsatellite markers. Three TGMS donors, Norin PL 12 (tms2), SA2 (tgms) and DQ200047-21 (tms5) were utilized in generating crosses from which two-gene and three-gene pyramids possessing the RM11 allele of Norin PL 12, RM257 allele of SA2 and RM174 allele of DQ200047-21 were selected. All selected progenies were male-sterile at sterility-inducing conditions. In addition, rice SF21 was identified as a candidate tms5 gene because of its complete linkage with RM174. The 4,200-bp region was amplified from the TGMS line M105S and the two ends were sequenced. In silico analysis of partial nucleotide sequences showed that the region is similar to the SF21 pollen-specific gene of Arabidopsis and Helianthus. The M105S tms5 sequence was also compared to the SF21 sequence from the International Rice Genome Sequencing Project (IRGSP) database.     

Meta-QTL analysis and identification of candidate genes related to root traits in maize

Maize root system architecture determines key functions of uptake of water and nutrients in plants. A large number of quantitative trait loci (QTLs) of root-related traits have been found in different populations of maize. Identification of consistent QTLs across diverse genetic backgrounds could be instrumental on marker-assisted selection of traits and identification of candidate functional genes. In this study, 20 published papers were investigated regarding on reported results of QTLs related to root traits of maize, and in total 428 individual QTLs for 23 root-related traits were used for meta-analysis, resulting in 53 Meta-QTLs (MQTLs) retrieved over ten maize chromosomes. Among these MQTLs regions, in total 45 maize homologs were considered as candidate genes affecting maize root traits by comparing with 7 genes from rice and 36 genes from Arabidopsis. Three maize genes (GRMZM5G813206, GRMZM2G167220 and GRMZM2G467069) identified from MQTL_8-5 could play important roles on lateral root and crown root development of maize. Two of the MQTLs, i.e. MQTL_7-2 and MQTL_9-1, involved in nitrogen (N) and phosphorus (P) stress responses and both of them with small physical distance (less than 3 Mb), could be used for abiotic stress improvement of maize root traits. These MQTLs and candidate genes will be helpful for future gene cloning and marker-assisted selection in maize.     

Diallel analyses reveal the genetic control of resistance to ascochyta blight in diverse chickpea and wild Cicer species

Ascochyta blight is a major fungal disease affecting chickpea production worldwide. The genetics of ascochyta blight resistance was studied in five 5 × 5 half-diallel cross sets involving seven genotypes of chickpea (ICC 3996, Almaz, Lasseter, Kaniva, 24B-Isoline, IG 9337 and Kimberley Large), three accessions of Cicer reticulatum (ILWC 118, ILWC 139 and ILWC 184) and one accession of C. echinospermum (ILWC 181) under field conditions. Both F₁ and F₂ generations were used in the diallel analysis. The disease was rated in the field using a 1–9 scale. Almaz, ICC 3996 and ILWC 118 were the most resistant (rated 3–4) and all other genotypes were susceptible (rated 6–9) to ascochyta blight. Estimates of genetic parameters, following Hayman’s method, showed significant additive and dominant gene actions. The analysis also revealed the involvement of both major and minor genes. Susceptibility was dominant over resistance to ascochyta blight. The recessive alleles were concentrated in the two resistant chickpea parents ICC 3996 and Almaz, and one C. reticulatum genotype ILWC 118. The wild Cicer accessions may have different major or minor resistant genes compared to the cultivated chickpea. High narrow-sense heritability (ranging from 82% to 86% for F₁ generations, and 43% to 63% for F₂ generations) indicates that additive gene effects were more important than non-additive gene effects in the inheritance of the trait and greater genetic gain can be achieved in the breeding of resistant chickpea cultivars by using carefully selected parental genotypes.     

Genetic components of pod shattering in soybean

Half diallel crosses among ten pure breeding lines of soybean were made in 1997 and 1998 to study the inheritance of pod shattering in soybean. Evaluation for pod shattering among F₂ segregating populations was carried out in an oven set at 80 ^°C for 12 hours. Diallel analysis was carried out to estimate genetic parameters and detect presence of non allelic interaction of genes affecting pod shattering. Hayman's diallel analysis indicated significant variation of Wr + Vr and Wr – Vr over arrays, suggesting epistatic gene action. Similarly results from a joint regression coefficient over replications were significantly (p < 0.05) different from unity and zero, suggesting presence of non allelic interaction of genes. The intercept was positive, suggesting partial dominance for the shattering trait. Both general combining ability (GCA) and specific combining ability (SCA) effects were significant (p < 0.05). This revised version was published online in July 2006 with corrections to the Cover Date.     

Fine mapping of a major quantitative trait locus, <Emphasis Type="Italic">qFLL6.2</Emphasis>, controlling flag leaf length and yield traits in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Fine mapping of a quantitative trait locus, qFLL6.2, controlling flag leaf length (FLL) and yield traits in rice was conducted using four sets of near isogenic lines (NILs) that were developed from a common residual heterozygote at F₇ generation of the indica rice cross Zhenshan 97/Milyang 46. Each of the NIL sets consisted of 40 lines that are S₁ progenies of ten maternal homozygotes, ten paternal homozygotes, and 20 heterozygotes differing in a portion of the 1.19-Mb interval RM3414–RM6917 on the short arm of rice chromosome 6. Analysis of phenotypic differences among the three genotypic groups in each NIL set delimited qFLL6.2 to a 62.1-kb region flanked by simple sequence repeat marker RM3414 and sequence-tagged site marker Si2944. This QTL explained 52.73% of the phenotypic variance, and the Zhenshan 97 allele increased FLL by 2.40 cm. Based on data collected from homozygous lines of three of the NIL sets, qFLL6.2 was shown to have major effects on all the three yield traits analyzed, including the number of spikelets per panicle, the number of filled grains per panicle, and grain weight per panicle. A comparison of the different groups revealed that the effect of qFLL6.2 was highly consistent across different genetic backgrounds and environments, providing a good candidate for map-based cloning and investigating the source–sink relationship in rice.     

Two chromosome segments confer multiple potyvirus resistance in maize

Potyviruses cause serious yield losses in maize production worldwide. While the maize dwarf mosaic virus (MDMV) predominates in the USA, sugarcane mosaic virus (SCMV) is a major pathogen in China and Germany. In previous studies, inbred FAP1360A revealed complete resistance against both MDMV and SCMV. Two major SCMV resistance genes, Scmv1 and Scmv2, were located on chromosomes 6 and 3, respectively, in populations derived from crosses with the susceptible inbred line F7. For validation of these results obtained in segregating backcross‐ or F_2:3‐populations, near‐isogenic lines to F7 have been produced after one initial cross to FAP1360A by repeated backcrossing to F7, phenotypic selection for SCMV resistance, and marker‐assisted selection for the Scmv1 and Scmv2 regions from FAP1360A. The near‐isogenic line F7R has been studied in detail both at the genomic level and for resistance to different potyviruses. Based on 112 polymorphic simple sequence repeat markers, F7R received genomic segments introgressed from FAP1360A exclusively in the Scmv1 and Scmv2 chromosomal regions. F7R conferred complete resistance to SCMV and MDMV, but also to zea mosaic virus and to systemic infection by wheat streak mosaic virus. FAP1360A, F7, F7R were not systemically infected by high plains virus. Thus, introgression of Scmv1 and Scmv2 from FAP1360A into F7 was sufficient to generate the first potyvirus multiresistant European Flint line reported so far.     

Doubled haploids in tropical maize: <Emphasis Type="SmallCaps">II</Emphasis>. Quantitative genetic parameters for testcross performance

Single crosses (SC) of elite inbreds and open-pollinated populations (OP) are suitable source germplasm for doubled haploid (DH) line development in hybrid maize breeding, given that they combine a high population mean ([`(x)] \overline{x} ) for testcross performance with adequate response to selection ( \Updelta G \Updelta G ). This is the first study reporting testcross grain yield (TCGY) and dry matter content (TCDMC) evaluations of 131 DH lines developed from ten tropical source germplasm comprising five OP (OP1–OP5) and five SC (SC1–SC5). Gene diversity (d) and the average number of alleles (a <sub>r</sub> ) per locus was estimated for DH lines based on 24 simple sequence repeat markers. Analysis across three environments revealed no significant differences between [`(x)] \overline{x} of OP- and SC-derived DH lines for TCGY and TCDMC. Significant genetic variance for both traits was only detected among OP-derived DH lines which may be explained by a larger number of segregating quantitative trait loci (QTL) as suggested by higher d and a _r values than in SC-derived DH lines. The usefulness criterion ( U = [`(x)] + \Updelta G U = \overline{x} + \Updelta G ) was higher for OP-derived DH lines for TCDMC, but higher for SC-derived DH lines for TCGY. DH lines from OP1, OP2, and OP3 showed high TCGY, suggesting that they may be useful in tropical hybrid breeding. We conclude that tropical OP represent a valuable source of untapped genetic variation that can efficiently be exploited with DH technology for hybrid maize breeding.     

Inheritance of high oleic acid content in safflower

Safflower (Carthamus tinctorius L.) oil with high oleic acid content (>75%) has a great value for both food and non-food uses. The trait has been reported to be environmentally stable and controlled by recessive alleles at one single gene Ol, even though the influence of modifying genes has been suggested. Additionally, germplasm with higher oleic acid content (>85%) has been reported. The objective of the present research was to study the inheritance of high oleic acid content in genetic sources with both levels of high oleic acid content (>75 and >85%, respectively). A genetic study was conducted by crossing the nuclear male-sterile line CL1 (18% oleic acid) and the high oleic acid lines CR-6 (80%) and CR-9 (87%). The evaluation of the F₁ and F₂ seed generations of the crosses CL1 × CR-6 and CL1 × CR-9 indicated that in both cases the high oleic acid trait was controlled by partially recessive alleles at a single locus. The observation of F₂, F₃, and F₄ segregants with high oleic acid phenotype but lower oleic acid levels than the parents revealed the presence of modifying genes affecting the trait. Crosses between the two high oleic acid lines produced no transgressive segregation other than that caused by the mentioned modifying genes, suggesting that the high oleic acid lines CR-6 and CR-9 share the same alleles at the Ol locus. Differences for oleic acid content between both lines were hypothesized to be produced by the accumulation of genes with a minor effect on the trait.     

Mapping QTLs of traits contributing to yield and analysis of genetic effects in tetraploid cotton

Fiber yield and yield components – including lint index (LI), seed index (SI), lint yield (LY), seed cotton yield (SCY) and number of seeds per boll (NSPB) – were investigated on the farm of Huazhong Agricultural University in a population of 69 F₂ individuals and corresponding F_2:3 families derived from a cross between high-fiber-yield Gossypium hirsutum CV Handan 208 and a low-fiber-yield Gossypium barbadense CV Pima 90. On the basis of the genetic map constructed previously from the same population by Lin et al. (Plant Breed., 2005), quantitative trait locus (QTL) analysis was performed with the software QTL Cartographer V2.0 using composite interval mapping method (LOD ≥ 3.0). A total of 21 QTLs were identified, which were located in 15 linkage groups. The number of QTLs per trait ranged from one to seven. Of these QTLs detected, one affecting LI explained 24.3% of phenotypic variation (PV), five influencing SI explained 16.15–39.21% of PV, seven controlling LY explained 13.01–28.35% of PV, and two controlling SCY explained 22.76 and 39.97% of PV, respectively. Simultaneously, the detected six QTLs for NSPB were located on five linkage groups, which individually explained 28.01–38.32% of the total phenotypic variation. The results would give breeders further insight into the genetic basis of fiber yield.