Quantitative Trait Loci For Height Research Articles

Understanding the genetic control of lodging-associated plant characters in winter wheat (Triticum aestivum L.)

A genetic analysis of plant characters associated with lodging resistance, yield and other agronomic traits was made on two doubled haploid winter wheat populations grown at two UK locations in the 2004/2005, 2005/2006 and 2006/2007 seasons. Wide genetic variation was found for traits that affect lodging, including plant height, components of stem strength (stem diameter, wall width and material strength), components of anchorage strength (spread and depth of the root plate), ear area and shoot number per plant. Heritabilities were estimated for each of the key lodging traits, with plant height having the highest heritability and anchorage traits the lowest values. Six quantitative trait loci (QTL) controlling plant height had individual height effects (2 × the additive effect) of 3–9 cm and taken together, could potentially increase plant height by up to 34 cm. Three of the height QTL were also associated with greater yield or greater thousand grain weight, and three were associated with components of stem strength or anchorage strength. QTL were also identified for each of the measured lodging traits, which were unrelated to height. Individual QTL with the largest estimated effects on lodging resistance were for height, stem diameter, stem material strength, stem failure moment, root plate spread and root plate depth. Diagnostic genetic markers for the most important QTL regions are now required to enable breeders to efficiently combine multiple traits together in a single variety that will increase lodging resistance and yield simultaneously.

QTL mapping for maize resistance and yield under infestation with Sesamia nonagrioides

The Mediterranean corn borer (MCB) is the most important maize insect pest in the Mediterranean region. The main objective was to map quantitative trait loci (QTL) for yield performance under infestation with MCB, resistance and agronomic traits in a maize RIL population derived from an inbred cross European flint × Reid. Six QTL for resistance traits were located: one QTL for tunnel length (bin 9.03; p = 19.8 %), one QTL for stalk lodging (bin 3.07, p = 11.5 %), and four QTL for ear resistance (bins 1.07, 5.03/5.05, and 8.04; p = 25–63 %). Twelve QTL for agronomic traits were located: a QTL for yield under infestation (bin 5.03, p = 15 %); two QTL for grain moisture (bins 1.07 and 8.05); two QTL for days to anthesis (bin 1.07 and 8.05); two QTL for days to silking (bins 8.04 and 10.02); three QTL for plant height (bins 5.04, 8.05 and 9.03); and two QTL for ear height (bins 8.05 and 9.03). No genetic correlations between yield and other traits were observed. The cross validation (CV) approach showed that the estimation biases for QTL for resistance traits were higher than those for agronomic traits. This work stresses the importance of the region 9.03 for controlling corn borer resistance and suggests the presence of QTL with small effect on ear-resistance traits. At the same genomic region, there are also genes that control plant and ear height and future works could elucidate whether these genes are the same or are closely linked. The QTL for yield seem to play an important role in MCB tolerance in this genetic background. Large biases observed for QTL effects by CV were mainly due to the small sample size used and were higher for resistance traits due to their larger genetic complexity. We consider that it is more appropriate to select for grain yield under infestation instead of selecting for resistance traits because resistance to MCB could have unfavorable associations with agronomic traits.

Genes and Quantitative Trait Loci Controlling Biomass Yield and Forage Quality Traits in Perennial Wildrye

ABSTRACTNative perennial grasses have potential as low‐input biomass feedstocks. Basin wildrye [Leymus cinereus (Scribn. & Merr.) Á. Löve] is the largest native grass in western North America but is susceptible to defoliation. Creeping wildrye [Leymus triticoides (Buckley) Pilg.] is a shorter less productive grass with durable rhizomes and higher forage quality. Two creeping wildrye pseudo‐backcross populations derived from interspecific hybrids were used to identify quantitative trait loci (QTL) controlling plant height, rhizome spreading, flowering, postanthesis biomass yield, cellulosic fiber, lignin, and protein traits using a linkage map comprising 376 expressed sequence tags and 423 other DNA markers. Biomass yields of the F1 hybrids and pseudo‐backcross populations were significantly greater than creeping wildrye with some genotypes nearly equal to or greater than basin wildrye. Rhizome spreading and forage quality of the creeping wildrye pseudo‐backcross populations were significantly greater than basin wildrye. Six of nine plant height QTL overlap with biomass QTL. Three flowering QTL detected in both populations overlap with fiber QTL. Plant height and flowering QTL were aligned to genes controlling dwarfing, photoperiod response, and vernalization in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) using the Brachypodium distachyon (L.) P. Beauv. genome reference sequence. Evidence suggests that genetic mechanisms controlling plant height and flowering are conserved among temperate grasses and reveals pathways for improving biomass production and forage quality.

A new genetic linkage map of barley (Hordeum vulgare L.) facilitates genetic dissection of height and spike length and angle

Plant height and spike length and angle are important agronomic traits in the production of barley (Hordeum vulgare L.) due to strong correlations with lodging and disease. The objective of this study was to use QTL analysis to identify genetic regions associated with each trait in a recombinant inbred line (RIL) mapping population derived from a cross of Falcon by Azhul. Falcon is a spring six-row hulless feed barley with long spikes displaying obtuse angles, while Azhul is a spring dwarf, six-row hulless food barley with short spikes displaying acute angles. The population was genotyped using SNP, DArT and SSR markers and quantitative trait loci (QTL) were detected on chromosomes 2H (102.8cM, spike length), 3H (89.2cM, plant height and 38.2, spike angle and length), 4H (19.0cM, spike length), and 5H (106.7cM, spike angle). In conclusion, we developed a barley genetic map, which incorporated SNP, DArT and SSR markers, for detection of height and spike length and angle QTL. Three spike angle, one spike length and one plant height QTL were novel and by using comparative genomics we identified possible candidate genes involved in gibberellic acid signaling and auxin- and ethylene-responsive pathways. This knowledge can be used to generate suitable markers for barley breeding improvement.

Expression Levels of LCORL Are Associated with Body Size in Horses

Body size is an important characteristic for horses of various breeds and essential for the classification of ponies concerning the limit value of 148 cm (58.27 inches) height at the withers. Genome-wide association analyses revealed the highest associated quantitative trait locus for height at the withers on horse chromosome (ECA) 3 upstream of the candidate gene LCORL. Using 214 Hanoverian horses genotyped on the Illumina equine SNP50 BeadChip and 42 different horse breeds across all size ranges, we confirmed the highly associated single nucleotide polymorphism BIEC2-808543 (−log10P = 8.3) and the adjacent gene LCORL as the most promising candidate for body size. We investigated the relative expression levels of LCORL and its two neighbouring genes NCAPG and DCAF16 using quantitative real-time PCR (RT-qPCR). We could demonstrate a significant association of the relative LCORL expression levels with the size of the horses and the BIEC2-808543 genotypes within and across horse breeds. In heterozygous C/T-horses expression levels of LCORL were significantly decreased by 40% and in homozygous C/C-horses by 56% relative to the smaller T/T-horses. Bioinformatic analyses indicated that this SNP T>C mutation is disrupting a putative binding site of the transcription factor TFIID which is important for the transcription process of genes involved in skeletal bone development. Thus, our findings suggest that expression levels of LCORL play a key role for body size within and across horse breeds and regulation of the expression of LCORL is associated with genetic variants of BIEC2-808543. This is the first functional study for a body size regulating polymorphism in horses and a further step to unravel the mechanisms for understanding the genetic regulation of body size in horses.

A major QTL for plant height is linked with bloom locus in sorghum [Sorghum bicolor (L.) Moench

Plant height is one of the most important agronomic traits in sorghum with its relevance for biomass, grain yield, fodder and lodging. To understand its genetic basis, the quantitative trait loci (QTL) were identified using a recombinant inbred line (RIL) population consisting of 168 RILs derived from the cross between the two sorghum inbred lines 296B (dwarf) and IS18551 (tall) over six seasons. Two major QTL were identified one each on chromosomes SBI-06 and SBI-07 corresponding to the Dw2 and Dw3 gene loci together accounting 41 % plant height variation. In addition, a morphological bloom trait locus which remained unlinked in the linkage map was found to be significantly linked with plant height in single marker analysis explaining 22 % of the trait variation. By comparing the map positions of Dw1, Dw2 and Dw3, the new locus for plant height linked with bloom is proposed as Dw4 locus. Both SSR and the morphological bloom loci linked with height QTL of the present study can be employed as effective tools in marker-assisted breeding for rapid conversion of selected inbred parent lines either as dwarf seed (male sterile) parents or taller pollinators for hybrid seed industry, or for developing high biomass lines in sweet sorghum for exploitation as high bio-fuel crop.

Genetic map construction and quantitative trait locus (QTL) analysis on growth-related traits in common carp (Cyprinus carpio L.)

Common carp (Cyprinus carpio L.) is one of the most widely distributed freshwater species in the world with important values in aquaculture, however, its quantitative trait loci (QTLs) associated to growth-related traits have been rarely identified. In this study, using F2 populations derived from a cross between Purse red common carp (C. carpio var. wuyuanensis) and Xingguo red common carp (C. carpio var.singuonensis), a genetic linkage map of common carp based on amplified fragment length polymorphisms (AFLP) and microsatellite (SSR) markers was constructed, meanwhile QTL analysis were conducted for growth-related traits. A total of 347 AFLP and 22 SSR markers were assembled on the map, which comprised 50 linkage groups and covered 5608.1cM Kosambi. A total of 25 QTLs were identified for growth-related traits, including four QTLs for body weight, one QTL for total length, four QTLs for standard length, six QTLs for body height, eight QTLs for caudal peduncle length and two QTLs for caudal peduncle height, which explained 0.05 to 61.40% of phenotypic variation. Meanwhile, comparison of linkage maps between common carp and zebrafish was also conducted, providing a new insight into the genetic base of the QTL affecting the growth-related traits. This study will be useful for conducting marker-assisted selection (MAS) breeding programs in common carp. Key words: Cyprinus carpio, F2 populations, amplified fragment length polymorphisms, microsatellite, quantitative traits locus.

Quantitative trait loci (QTL) for Fusarium ELISA compared to QTL for Fusarium head blight resistance and deoxynivalenol content in barley

With 1 figure and 3 tablesAbstractFusarium head blight (FHB) and deoxynivalenol (DON) mycotoxin produced by Fusarium graminearum reduce barley yield and quality worldwide. An enzyme‐linked immunosorbent assay (ELISA) using an antibody specific to Fusarium was proposed as an alternative for measuring FHB instead of counting infected kernels per spike. Cleistogamy (closed flowering) may be an avoidance mechanism for FHB resistance. This study was conducted to determine whether quantitative trait loci (QTL) for Fusarium ELISA were colocated with QTL for FHB, DON, heading date, height and spike density and/or the gene for cleistogamy. Doubled haploid lines from Zhedar 2/ND9712//Foster were tested in ten environments and used to develop a 260‐marker linkage map. QTL analysis located 24 significant regions for the six traits. The effect of cleistogamy on resistance was unclear and environment specific. Of the two QTL located for ELISA, only one corresponded with a QTL for FHB, but large allelic differences in ELISA were found for the regions significantly associated with FHB and DON, indicating that ELISA could be a simpler method to identify lines with FHB resistance and low DON.

Molecular dissection of plant height QTLs using recombinant inbred lines from hybrids between common wheat (Triticum aestivum L.) and spelt wheat (Triticum spelta L.)

In wheat, plant height is an important agronomic trait, and a number of quantitative trait loci (QTLs) controlling plant height have been located. In this study, using the conditional and unconditional QTL mapping methods, combined with data from five different growth stages over two years of field trials, the developmental behavior for plant height in wheat was dissected. Nine unconditional QTLs and 8 conditional QTLs were identified, of which 6 were detected by both methods. None of the 11 QTLs was detected at all of the 5 investigated developmental stages, but 7 QTLs were detected at certain stages in both years. Further analysis identified 9 unconditional QTLs at different stages, which could explain the phenotypic variation from 4.81% to 17.35%. It was noteworthy that one major QTL designated QHt-4B-2, which was located on chromosome 4B, was detected on May 18 and 25 in both years, and its genetic contributions to plant height ranged from 13.42% to 16.13%. Moreover, of the 8 conditional QTLs identified, six were detected in both years, in the order of QHt-3B→QHt-4B-1→QHt-4B-2→QHt-4D→QHt-5A and QHt-2B expressed at the same developmental stage. The results indicate that QTL expression during plant height development is selective and in a temporal order.

Mapping QTL for Agronomic Traits on Wheat Chromosome 3A and a Comparison of Recombinant Inbred Chromosome Line Populations

ABSTRACTVariation for wheat (Triticum aestivumL.) grain yield and agronomic traits was used to map quantitative trait loci (QTL) in a ‘Cheyenne’ (CNN) × [CNN (‘Wichita’ 3A)] recombinant inbred chromosome line (RICL) population consisting of 223 CNN(RICLs3A) and 7 check cultivars that were evaluated in six environments in Nebraska during 2005–2007. A chromosome 3A linkage map spanning 106 cM was constructed using 32 microsatellite markers. Composite interval mapping detected 19 QTL for seven agronomic traits that individually accounted for 4.6 to 16.8% of the phenotypic variation. Three small genomic segments, spanning 3.4, 5.3, and 5.3 cM, contained most of the QTL. Two yield QTL were detected in two environments and in data pooled over environments. For grain volume weight, a QTL was detected in five of the six environments while a plant height QTL was detected in all environments. Wichita (WI) alleles contributed to the increased trait values for yield, spikes per square meter, and grain volume weight, while CNN contributed alleles to the increased 1000‐kernel weight, plant height, and anthesis date. Both CNN and WI contained alleles for increased number of kernels per spike. The 223 CNN(RICLs3A) set had greater power to detect QTL than the two smaller subsets—128 CNN(RICLs3A) developed using doubled haploids and 95 CNN(RICLs3A) developed using recombinant monosomic lines. Neither of the subsets performed consistently better than the other in detecting QTL.

Genetic Improvement of Sorghum as a Biofuel Feedstock: I. QTL for Stem Sugar and Grain Nonstructural Carbohydrates

Genetic improvement of sorghum [Sorghum bicolor (L.) Moench] has traditionally focused on a single nonstructural carbohydrate, either grain starch or stem sugar. Sorghum starch and sugar may both be used as feedstocks for biofuel production. To investigate genetic tradeoffs between grain and stem sugar, a population derived from sweet sorghum cultivar Rio and grain sorghum ‘BTx623’ was evaluated for 27 traits related to grain and stem sugar yield and composition. Across three environments, a total of 129 quantitative trait loci (QTL) were identified. Tradeoffs identified between grain and stem sugar yield QTL colocalized with height and flowering time QTL. Most importantly, QTL were identified that increased yield and altered the composition of stem sugar and grain without pleiotropic effects. For example, a QTL on chromosome 3 that explained 25% of the genetic variance for stem sugar concentration did not colocalize with any grain QTL. These results suggest that total nonstructural carbohydrate yield could be increased by selecting for major QTL from both grain and sweet sorghum types. We conclude that altering grain and stem sugar genetic potential for yield traits should lead to greater feedstock improvement than altering composition traits.

Multi-environment QTL mixed models for drought stress adaptation in wheat

Many quantitative trait loci (QTL) detection methods ignore QTL-by-environment interaction (QEI) and are limited in accommodation of error and environment-specific variance. This paper outlines a mixed model approach using a recombinant inbred spring wheat population grown in six drought stress trials. Genotype estimates for yield, anthesis date and height were calculated using the best design and spatial effects model for each trial. Parsimonious factor analytic models best captured the variance-covariance structure, including genetic correlations, among environments. The 1RS.1BL rye chromosome translocation (from one parent) which decreased progeny yield by 13.8 g m(-2) was explicitly included in the QTL model. Simple interval mapping (SIM) was used in a genome-wide scan for significant QTL, where QTL effects were fitted as fixed environment-specific effects. All significant environment-specific QTL were subsequently included in a multi-QTL model and evaluated for main and QEI effects with non-significant QEI effects being dropped. QTL effects (either consistent or environment-specific) included eight yield, four anthesis, and six height QTL. One yield QTL co-located (or was linked) to an anthesis QTL, while another co-located with a height QTL. In the final multi-QTL model, only one QTL for yield (6 g m(-2)) was consistent across environments (no QEI), while the remaining QTL had significant QEI effects (average size per environment of 5.1 g m(-2)). Compared to single trial analyses, the described framework allowed explicit modelling and detection of QEI effects and incorporation of additional classification information about genotypes.

Susceptibility to Fusarium head blight is associated with the Rht-D1b semi-dwarfing allele in wheat

Fusarium head blight (FHB) is an important disease of wheat worldwide. The cultivar Spark is more resistant than most other UK winter wheat varieties but the genetic basis for this is not known. A mapping population from a cross between Spark and the FHB susceptible variety Rialto was used to identify quantitative trait loci (QTL) associated with resistance. QTL analysis across environments revealed nine QTL for FHB resistance and four QTL for plant height (PH). One FHB QTL was coincident with the Rht-1D locus and accounted for up to 51% of the phenotypic variance. The enhanced FHB susceptibility associated with Rht-D1b is not an effect of PH per se as other QTL for height segregating in this population have no influence on susceptibility. Experiments with near-isogenic lines supported the association between susceptibility and the Rht-D1b allele conferring the semi-dwarf habit. Our results demonstrate that lines carrying the Rht-1Db semi-dwarfing allele are compromised in resistance to initial infection (type I resistance) while being unaffected in resistance to spread within the spike (type II resistance).

Mapping QTLs for Resistance to Frosty Pod and Black Pod Diseases and Horticultural Traits in Theobroma cacao L.

A heterozygous F1 mapping population of cacao (Theobroma cacao L.) was created and evaluated for resistance to frosty pod [caused by Moniliophthora roreri (Cif. and Par.) Evans et al.], and black pod [caused by Phytophthora palmivora (Butl.) Butl.] and for five horticultural traits at CATIE in Turrialba, Costa Rica. The population consisted of 256 F1 progeny from the cross ‘Pound 7’ × ‘UF 273’. Progeny were used to form a linkage map using 180 markers. The linkage map contained 10 linkage groups (LGs), numbered as the LG in the cacao reference map, and was used to locate putative quantitative trait loci (QTL) for resistance to the aforementioned diseases and five horticultural traits. Resistance to frosty pod was measured by internal and external pod resistance. Five QTLs for frosty pod resistance were found on three LGs, 2, 7, and 8, with UF 273 appearing to be the source of resistance. These alleles are being used for scoring progeny in ongoing cooperative marker‐assisted selection projects, and constitute the first QTLs identified for frosty pod resistance. Three QTLs for black pod resistance were found on LG 4, 8, and 10, with the most favorable alleles coming from Pound 7. One QTL was found on LG 4 for average trunk growth rate, and two QTLs for height of first jorquette were identified on LGs 4 and 6. One QTL each for average trunk diameter growth and pod color was found on LG 4.

Seed and agronomic QTL in low linolenic acid, lipoxygenase-free soybean (Glycine max(L.) Merrill) germplasm

Linolenic acid and seed lipoxygenases are associated with off flavours in soybean products. F5 recombinant inbred lines (RILs) from a cross between a low linolenic acid line (RG10) and a seed lipoxygenase-free line (OX948) were genotyped for simple sequence repeats (SSR), random amplified polymorphic DNA (RAPD), sequence-tagged sites (STS), and cleaved amplified polymorphic sequence (CAPS) markers and evaluated for seed and agronomic traits at 3 Ontario locations in 2 years. One hundred twenty markers covering 1247.5 cM were mapped to 18 linkage groups (LGs) in the soybean composite genetic map. Seed lipoxygenases L-1 and L-2 mapped as single major genes to the same location on LG G13-F. L-3 mapped to LG G11-E. This is the first report of a map position for L-3. A major quantitative trait locus (QTL) associated with reduced linolenic acid content was identified on LG G3-B2. QTLs for 12 additional seed and agronomic traits were detected. Linolenic acid content, linoleic acid content, yield, seed mass, protein content, and plant height QTL were present in at least 4 of 6 environments. Three to 8 QTLs per trait were detected that accounted for up to 78% of total variation. Linolenic acid and lipoxygenase loci did not overlap yield QTL, suggesting that it should be possible to develop high-yielding lines resistant to oxidative degradation by marker-assisted selection (MAS).

QTL analysis of quality traits in the spring wheat cross RL4452 × ‘AC Domain’

AbstractWheat grain quality is a complex group of traits of tremendous importance to wheat producers, end‐users and breeders. Quantitative trait locus (QTL) analysis studied the genetics of milling, mixograph, farinograph, baking, starch and noodle colour traits in the spring wheat population RL4452/‘AC Domain’. Forty‐seven traits were measured on the population and 99 QTLs were detected over 18 chromosomes for 41 quality traits. Forty‐four of these QTLs mapped to three major QTL clusters on chromosomes 1B, 4D, and 7D. Fourteen QTLs mapped near Glu‐B1, 20 QTLs mapped near a major plant height QTL on chromosome 4D, and 10 QTLs mapped near a major time to maturity QTL on chromosome 7D. Large QTLs were detected for grain and flour protein content, farinograph absorption, mixograph parameters, and dietary fibre on chromosome 2BS. QTLs for yellow alkaline noodle colour parameter L* mapped to chromosomes 5B and 5D, while the largest QTL for the b* parameter mapped to 7AL.

Linkage analysis of quantitative traits for obesity, diabetes, hypertension, and dyslipidemia on the island of Kosrae, Federated States of Micronesia.

Obesity, diabetes, hypertension, and heart disease are highly heritable conditions that in aggregate are the major causes of morbidity and mortality in the developed world and are growing problems in developing countries. To map the causal genes, we conducted a population screen for these conditions on the Pacific Island of Kosrae. Family history and genetic data were used to construct a pedigree for the island. Analysis of the pedigree showed highly significant heritability for the metabolic traits under study. DNA samples from 2,188 participants were genotyped with 405 microsatellite markers with an average intermarker distance of 11 cM. A protocol using loki, a Markov chain Monte Carlo sampling method, was developed to analyze the Kosraen pedigree for height, a model quantitative trait. Robust quantitative trait loci for height were found on 10q21 and 1p31. This protocol was used to map a set of metabolic traits, including plasma leptin to chromosome region 5q35; systolic blood pressure to 20p12; total cholesterol to 19p13, 12q24, and 16qter; hip circumference to 10q25 and 4q23; body mass index to 18p11 and 20q13; apolipoprotein B to 2p24-25; weight to 18q21; and fasting blood sugar to 1q31-1q43. Several of these same chromosomal regions have been identified in previous studies validating the use of loki. These studies add information about the genetics of the metabolic syndrome and establish an analytical approach for linkage analysis of complex pedigrees. These results also lay the foundation for whole genome scans with dense sets of SNPs aimed to identifying causal genes.

The effect of semi-dwarf genes on root system size in field-grown barley

Root system size (RSS) was measured in 12 diverse barley genotypes and 157 double-haploid lines (DHs), using electric capacitance. The parents of the DHs, Derkado and B83-12/21/5, carry different semi-dwarfing genes, sdw1 and ari-e.GP, respectively. Estimates of RSS were taken in the field thrice during plant development: stem elongation (RSS1), heading (RSS2) and grain filling (RSS3). The 12 barley genotypes were assessed over 3 years and at two or three locations each year; the DH mapping population was assessed at two locations in 2002. Among the 12 barley genotypes, those with the semi-dwarf genes had greater RSS values in all 3 years (28.9, 24.6 and 15.0% in years 1, 2 and 3, respectively) compared to non-semi-dwarf controls. The DH population showed transgressive segregation on both sides of the parent means, indicating polygenic control of RSS. Quantitative trait loci (QTLs) for RSS were found on five of the seven chromosomes: 1H, 3H, 4H, 5H and 7H and these were compared with previously mapped agronomic traits. The TotalRSS QTL on 3H was associated with sdw1 and QTLs for height, plant yield and plant weight. The RSS3 QTL on 5H was associated with ari-e.GP and QTLs for height, plant yield, plant weight, harvest index and tiller number. The RSS3 QTL on 7H was also associated with a TotalRSS QTL and QTLs for plant weight and harvest index. Other RSS QTLs were not associated with any other trait studied. RSS is considered to be a polygenic trait linked to important traits, in particular to yield. The study highlights the effects of semi-dwarfing genes and discusses the potential for breeding for root traits.

Genetic Components of Resistance to Stalk Tunneling by the European Corn Borer in Maize

Identification of the genes conferring resistance to European corn borer (ECB) [Ostrinia nubilalis (Hubner)] is an important step in understanding how resistance is expressed and whether different sources of maize (Zea mays L.) germplasm can be combined to enhance protection. The locations of genes for resistance to ECB tunneling have been reported but are inconsistent across studies. The objectives of this study were to map and characterize quantitative trait loci (QTL) for resistance to tunneling in De811 and compare these with related studies and with QTL for anthesis and ear height. Inbred De811 (resistant) was crossed to susceptible inbred B73 to produce a population of 147 F 3 lines. The population was artificially infested and evaluated in three environments. The F 3 lines were genotyped at 88 restriction fragment length polymorphism (RFLP) loci to facilitate QTL mapping with composite interval mapping (CIM). Seven QTL for ECB tunneling were detected on chromosomes 1, 3, 4, 5, and 8, associated with 42% of the phenotypic variation. The F, exhibits partial dominance for resistance but only one QTL with dominant gene action was observed. An F 3 population of B73 x B52 that was evaluated in the same environments facilitated comparisons of genetic heterogeneity between inbreds De811 and B52. Only one QTL for tunneling was common between the populations, indicating that the two inbreds may contribute different genes for resistance in crosses with B73. This information could be useful for combining the favorable alleles of De811 and B52.

Improvement of hybrid yield by advanced backcross QTL analysis in elite maize.

We applied an advanced backcross breeding strategy to identify quantitative trait loci (QTLs) of agronomic importance in a cross between two elite inbreds of maize, RD6502 (Mo17-type recurrent parent) and RD3013 (Iodent donor parent). Two hundred and four BC(2) families were scored at 106 SSR, 15 AFLP, and 38 Heartbreaker (MITE) loci. BC(2) testcrosses (TC) with B73 were phenotyped at six locations in the Midwest and N.Y. We detected four grain yield, six grain moisture, and three plant height QTLs at which the RD3013 allele had a favorable effect ( p < 0.05). All four yield QTLs were selected as target introgressions in the development of BC(3)TC families. As predicted by BC(2)TC analysis, BC(3)TC entries containing introgressions at yld3.1 and yld10.1 significantly outperformed non-carrier entries by 11.1% (15.6 bu/A at one location) and 6.7% (7.1 bu/A averaged across two locations), respectively, in replicated Midwestern trials ( p < 0.05). Detection of yld10.1 effects in the BC(2)TC by spatial analysis (i.e., incomplete block, response surface, autoregressive, moving average or autoregressive moving average), but not by conventional single point analysis or interval mapping, indicated the utility of local environmental control for QTL mapping in unreplicated maize progeny. This work demonstrated that the advanced backcross QTL method can be applied to identify and manipulate useful QTLs in heterotic inbreds of elite maize. Genetic gains by this approach can be coupled with the maintenance and selection of favorable epistatic gene complexes by traditional hybrid breeding for maize improvement.