Precise mapping of quantitative trait loci for resistance to southern leaf blight, caused by Cochliobolus heterostrophus race O, and flowering time using advanced intercross maize lines

The intermated B73 × Mo17 (IBM) population, an advanced intercross recombinant inbred line population derived from a cross between the maize lines B73 (susceptible) and Mo17 (resistant), was evaluated in four environments for resistance to southern leaf blight (SLB) disease caused by Cochliobolus heterostrophus race O. Two environments were artificially inoculated, while two were not inoculated and consequently had substantially lower disease pressure. Four common SLB resistance quantitative trait loci (QTL) were identified in all environments, two in bin 3.04 and one each in bins 1.10 and 8.02/3. There was no significant correlation between disease resistance and days to anthesis. A direct comparison was made between SLB QTL detected in two populations, independently derived from the same parental cross: the IBM advanced intercross population and a conventional recombinant inbred line population. Several QTL for SLB resistance were detected in both populations, with the IBM providing between 5 and, in one case, 50 times greater mapping resolution.     

Mapping quantitative trait loci associated with southern leaf blight resistance in maize (Zea mays L.)

Southern leaf blight (SLB) caused by the fungus Cochliobolus heterostrophus (Drechs.) Drechs. is a major foliar disease of maize worldwide. Our objectives were to identify quantitative trait loci (QTL) for resistance to SLB and flowering traits in recombinant inbred line (RIL) population derived from the cross of inbred lines LM5 (resistant) and CM140 (susceptible). A set of 207 RILs were phenotyped for resistance to SLB at three time intervals for two consecutive years. Four putative QTL for SLB resistance were detected on chromosomes 3, 8 and 9 that accounted for 54% of the total phenotypic variation. Days to silking and anthesis–silking interval (ASI) QTL were located on chromosomes 6, 7 and 9. A comparison of the obtained results with the published SLB resistance QTL studies suggested that the detected bins 9.03/02 and 8.03/8.02 are the hot spots for SLB resistance whereas novel QTL were identified in bins 3.08 and 8.01/8.04. The linked markers are being utilized for marker‐assisted mobilization of QTL conferring resistance to SLB in elite maize backgrounds. Fine mapping of identified QTL will facilitate identification of candidate genes underlying SLB resistance.     

Targeted discovery of quantitative trait loci for resistance to northern leaf blight and other diseases of maize

To capture diverse alleles at a set of loci associated with disease resistance in maize, heterogeneous inbred family (HIF) analysis was applied for targeted QTL mapping and near-isogenic line (NIL) development. Tropical maize lines CML52 and DK888 were chosen as donors of alleles based on their known resistance to multiple diseases. Chromosomal regions (“bins”; n = 39) associated with multiple disease resistance (MDR) were targeted based on a consensus map of disease QTLs in maize. We generated HIFs segregating for the targeted loci but isogenic at ~97% of the genome. To test the hypothesis that CML52 and DK888 alleles at MDR hotspots condition broad-spectrum resistance, HIFs and derived NILs were tested for resistance to northern leaf blight (NLB), southern leaf blight (SLB), gray leaf spot (GLS), anthracnose leaf blight (ALB), anthracnose stalk rot (ASR), common rust, common smut, and Stewart’s wilt. Four NLB QTLs, two ASR QTLs, and one Stewart’s wilt QTL were identified. In parallel, a population of 196 recombinant inbred lines (RILs) derived from B73 × CML52 was evaluated for resistance to NLB, GLS, SLB, and ASR. The QTLs mapped (four for NLB, five for SLB, two for GLS, and two for ASR) mostly corresponded to those found using the NILs. Combining HIF- and RIL-based analyses, we discovered two disease QTLs at which CML52 alleles were favorable for more than one disease. A QTL in bin 1.06–1.07 conferred resistance to NLB and Stewart’s wilt, and a QTL in 6.05 conferred resistance to NLB and ASR.     

Identification of quantitative trait loci controlling resistance to gray leaf spot disease in maize

Breeding maize for gray leaf spot (GLS) resistance has been hindered by the quantitative nature of the inheritance of GLS resistance and by the limitations of selection under less than optimumal disease pressure. In order to identify the quantitative trait loci (QTLs) controlling GLS resistance, a cross was made between B73 (susceptible) and Va14 (resistant) to generate a large F₂ population. Six GLS disease assessments were made throughout the disease season for over 1000 F₂ plants in 1989, and for 600 F₂-derived F₃ lines replicated in two blocks in 1990. RFLP analysis for78 marker loci representing all ten maize chromosomes was conducted in 239 F₂ individuals including those with the extreme GLS disease phenotypes. The GLS disease scores of the three field evaluations, each averaged over six ratings, were separately used for the interval mapping in order to determine the consistency of the QTL effects. The heavy GLS disease pressure, meticulous disease ratings, and large population size of this study afforded us the sensitivity for detecting QTL effects. QTLs located on three chromosomes (1, 4, and 8) had large effects on GLS resistance, each explaining 35.0–56.0%, 8.8–14.3%, and 7.7–11.0% of the variance, respectively. These three QTL effects were remarkably consistent across three disease evaluations over 2 years and two generations. Smaller QTL effects were also found on chromosomes 2 and 5, but the chromosome-5 effect might be a false positive because it was not repeatable even in the same location. The chromosome-1 QTLs had the largest effect or highest R² reported for any quantitative trait to-date. Except for the chromosome-4 gene, which was from the susceptible parent B73, the resistance alleles at all QTL were derived from Va14. The resistance QTLs on chromosomes 1 and 2 appear to have additive effects, but those on chromosomes 4 and 8 are dominant and recessive, respectively. Significant interaction between the QTLs on chromosomes 1 and 4 was detected in all three evaluations. Cumulatively, the four QTLs identified in this study explained 44, 60, and 68% of the variance in F₂, and in F₃ replications 1 and 2, respectively.     

Inheritance of resistance against northern leaf blight of maize using conventional breeding methods

Maize (Zea mays L.) is one of the important cereal crops along with wheat and rice worldwide. The purpose of this study was to use classical genetic approaches to assess the resistance of various maize parents and hybrids to the northern corn leaf blight (NCLB) disease in two different locations in Egypt. Eight parents, 28 F1, and 2 check hybrids were evaluated. The analysis of variance showed high significant variations between maize parents and their hybrids for the studied parameters and NCLB disease, besides there are significant variations between both locations. Results of maize parents showed that Sids 63, Giza 602, and Giza 628 cultivars exhibited the highest values and were resistant to NCLB in both locations comparing with Nubaria 39 and Gemmiza 18 that were susceptible to NCLB disease. Concerning the maize hybrids, analysis of variance and mean squares of growth characters in both locations indicated high significant variations between the maize hybrids including the check hybrids. When combined between the two locations for current parameters against NCLB, the data pointed that the Sakha location values for maize hybrids were much closed to the combining data in parents and the hybrids detected high resistance to this disease comparing with Nubaria location. All tested maize lines (38 lines), including parents and hybrids were classified as follows, two lines were rated as 1 (highly resistant), three were rated as 2 (resistant), sixteen were rated as 3 (moderate resistant), eight were rated 4 (moderately susceptible) and nine were rated 5 (susceptible). The data explaining that the crossing between high resistant maize cultivars produced high levels of resistance to NCLB disease. Therefore, our results verified that classical breeding could efficiently increase the resistance levels of maize germplasm against NCLB disease by developing new cultivars with superior performance in terms of grain yield, disease resistance and grain quality.     

Interval mapping of genes for quantitative resistance of maize to Setosphaeria turcica,cause of northern leaf blight,in a tropical environment

Quantitative trait loci (QTL) involved in the resistance of maize to Setosphaeria turcica, the causal agent of northern leaf blight, were located by interval mapping analysis of 121 F_2:3 lines derived from a cross between Mo17 (moderately resistant) and B52 (susceptible). A linkage map spanning 112 RFLP loci with 15 cM mean interval length was constructed, based on marker data recorded in a previous study. Field tests with artificial inoculation were conducted at three sites in tropical mid- to high-altitude regions of Kenya, East Africa. Host-plant response was measured in terms of incubation period, disease severity (five scoring dates), and the area under the disease progress curve (AUDPC). Heritability of all traits was high (around 0.75). QTL associated with the incubation period were located on chromosomes 2S and 8L. For disease severity and AUDPC, significant QTL were detected in the putative centromeric region of chromosome 1 and on 2S, 3L, 5S, 6L, 7L, 8L and 9S. On 2S the same marker interval which carried a gene enhancing latent period was also associated with reduced disease severity of juvenile plants. QTL on chromosomes 3L, 5S, 7L and 8L were significant across environments but all other QTL were affected by a large genotype x environment interaction. Partially dominant gene action for resistance as well as for susceptibility was prevailing. Single QTL explained 10 to 38% of the phenotypic variation of the traits. All but the QTL on chromosomes 1, 6 and 9 were contributed by the resistant parent Mo17. On chromosome 8L a QTL mapped to the same region as the major race-specific gene Ht2, supporting the hypothesis that some qualitative and quantitative resistance genes may be allelic.Abbreviations AUDPC area under the disease progress curve - CIMMYT International Maize and Wheat Improvement Center - KARI Kenya Agricultural Research Institute - NCLB northern corn leaf blight - QTL quantitative trait locus/loci     

Dissection of the barley 2L1.0 region carrying the 'Laevigatum' quantitative resistance gene to leaf rust using near-isogenic lines (NIL) and subNIL

Partial resistance to leaf rust (Puccinia hordei G. H. Otth) in barley is a quantitative resistance that is not based on hypersensitivity. This resistance hampers haustorium formation, resulting in a long latency period in greenhouse tests. The three most consistent quantitative trait loci (QTL) uncovered in the L94 x 'Vada' mapping population were introgressed by marker-assisted backcrossing into the susceptible L94 background to obtain near-isogenic lines (NIL). We also developed the reciprocal Vada-NIL for the susceptibility alleles of those QTL. The QTL Rphq2 affected latency period of P. hordei more than the QTL Rphq3 and Rphq4. The NIL confirmed the contribution of Rphq2 to partial resistance by prolonging the latency period by 28 h on L94-Rphq2 and shortening the latency period by 23 h on Vada-rphq2. On the basis of flanking restriction fragment length polymorphism-based markers, Rphq2 appeared to be located near the telomeric end of the long arm of chromosome 2H, in a physical region of high recombination, making it the target QTL for map-based cloning. Microscopic observations on the NIL confirmed the nonhypersensitive nature of the resistance conferred by Rphq2. A high-resolution genetic map of the Rphq2 region was constructed using a population of 38 subNIL with overlapping L94 introgressions in Vada background across the region. Rphq2 mapped approximately 2 centimorgans (cM) proximal from the MlLa locus. By bulked segregant analysis and use of synteny with rice, we developed additional markers and fine-mapped Rphq2 to a genetic interval of 0.11 cM that corresponds to a stretch of sequence of, at most, 70 kb in rice. Analysis of this rice sequence revealed predicted genes encoding two proteins with unknown function, retrotransposon proteins, peroxidase proteins, and a protein similar to a mitogen-activated protein kinase kinase kinase (MAP3K). Possible homologs of those peroxidases and MAP3K in barley are candidates for the gene that contributes to partial resistance to P. hordei.     

Durable resistance to two leaf blights in two maize inbred lines

Summary It has been determined that the occurrence of durable resistance as defined by Johnson and Kranz operates in maize inbred lines CM104 and CM105 against the leaf blight pathogens Setosphaeria turcica (= Exserohilum turcicum) and Drechslera maydis (=Cochliobolus heterostrophus), by analyzing data for 16 and 14 years, respectively. Essentially the methodology estimated the longevity of cultivar resistance by determining whether the regression coefficient of linear regression with years of testing and mean disease intensity is zero or not significantly different from zero. The values for both Turcicum Leaf Blight and Maydis Leaf Blight were not significantly different from zero. The resistant inbred lines have been used in hybrid combinations and have the potential to transmit this resistance to progenies in hybrid combinations that are governed by additive gene action.     

Characterization of disease resistance gene-like sequences in near-isogenic lines of tomato

 We examined near-isogenic lines (NILs) carrying either of the tomato mosaic virus (ToMV) resistance genes Tm-1 and Tm-2 for sequences homologous to the isolated disease-resistance genes. DNA fragments were amplified from the genomic DNA of the NILs by the polymerase chain reaction (PCR) using primers designed on the basis of sequences of certain domains conserved among some disease-resistance genes. Of ten PCR products cloned, five were identified as having homology to either of the two classes of disease-resistance genes. The first class encoded proteins containing leucine-rich repeats (LRRs) and a nucleotide-binding site (NBS), such as the RPS2 gene in Arabidopsis and the N gene in tobacco. The second class encoded proteins containing a C-terminal membrane anchor but no NBS, such as the Cf 2 and Cf 9 genes in tomato. In Southern hybridization of the genomic DNAs of the NILs carrying either Tm-1 or Tm-2 and their parental NIL carrying neither of these resistance genes, multiple bands could be detected with most of the clones used as probes. This suggests that the genomes of the NILs contain multiple copies of sequences homologous to some of the known disease-resistance genes. No evidence was obtained to show that the Tm-1 and/or Tm-2 loci encode either class of protein, since no polymorphic band patterns between the NILs were detected by Southern hybridization. Received: 15 August 1997 / Accepted: 2 September 1997     

The durable wheat disease resistance gene Lr34 confers common rust and northern corn leaf blight resistance in maize

Maize (corn) is one of the most widely grown cereal crops globally. Fungal diseases of maize cause significant economic damage by reducing maize yields and by increasing input costs for disease management. The most sustainable control of maize diseases is through the release and planting of maize cultivars with durable disease resistance. The wheat gene Lr34 provides durable and partial field resistance against multiple fungal diseases of wheat, including three wheat rust pathogens and wheat powdery mildew. Because of its unique qualities, Lr34 became a cornerstone in many wheat disease resistance programmes. The Lr34 resistance is encoded by a rare variant of an ATP‐binding cassette (ABC) transporter that evolved after wheat domestication. An Lr34‐like disease resistance phenotype has not been reported in other cereal species, including maize. Here, we transformed the Lr34 resistance gene into the maize hybrid Hi‐II. Lr34‐expressing maize plants showed increased resistance against the biotrophic fungal disease common rust and the hemi‐biotrophic disease northern corn leaf blight. Furthermore, the Lr34‐expressing maize plants developed a late leaf tip necrosis phenotype, without negative impact on plant growth. With this and previous reports, it could be shown that Lr34 is effective against various biotrophic and hemi‐biotrophic diseases that collectively parasitize all major cereal crop species.     

Limits on the reproducibility of marker associations with southern leaf blight resistance in the maize nested association mapping population

Background

A previous study reported a comprehensive quantitative trait locus (QTL) and genome wide association study (GWAS) of southern leaf blight (SLB) resistance in the maize Nested Association Mapping (NAM) panel. Since that time, the genomic resources available for such analyses have improved substantially. An updated NAM genetic linkage map has a nearly six-fold greater marker density than the previous map and the combined SNPs and read-depth variants (RDVs) from maize HapMaps 1 and 2 provided 28.5 M genomic variants for association analysis, 17 fold more than HapMap 1. In addition, phenotypic values of the NAM RILs were re-estimated to account for environment-specific flowering time covariates and a small proportion of lines were dropped due to genotypic data quality problems. Comparisons of original and updated QTL and GWAS results confound the effects of linkage map density, GWAS marker density, population sample size, and phenotype estimates. Therefore, we evaluated the effects of changing each of these parameters individually and in combination to determine their relative impact on marker-trait associations in original and updated analyses.

Results

Of the four parameters varied, map density caused the largest changes in QTL and GWAS results. The updated QTL model had better cross-validation prediction accuracy than the previous model. Whereas joint linkage QTL positions were relatively stable to input changes, the residual values derived from those QTL models (used as inputs to GWAS) were more sensitive, resulting in substantial differences between GWAS results. The updated NAM GWAS identified several candidate genes consistent with previous QTL fine-mapping results.

Conclusions

The highly polygenic nature of resistance to SLB complicates the identification of causal genes. Joint linkage QTL are relatively stable to perturbations of data inputs, but their resolution is generally on the order of tens or more Mbp. GWAS associations have higher resolution, but lower power due to stringent thresholds designed to minimize false positive associations, resulting in variability of detection across studies. The updated higher density linkage map improves QTL estimation and, along with a much denser SNP HapMap, greatly increases the likelihood of detecting SNPs in linkage with causal variants. We recommend use of the updated genetic resources and results but emphasize the limited repeatability of small-effect associations.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1068) contains supplementary material, which is available to authorized users.     

Use of selection with recurrent backcrossing and QTL mapping to identify loci contributing to southern leaf blight resistance in a highly resistant maize line

B73 is a historically important maize line with excellent yield potential but high susceptibility to the foliar disease southern leaf blight (SLB). NC292 and NC330 are B73 near-isogenic lines (NILs) that are highly resistant to SLB. They were derived by repeated backcrossing of an elite source of SLB resistance (NC250P) to B73, with selection for SLB resistance among and within backcross families. The goal of this paper was to characterize the loci responsible for the increased SLB resistance of NC292 and NC330 and to determine how many of the SLB disease resistance quantitative trait loci (dQTL) were selected for in the development of NC292 and NC330. Genomic regions that differentiated NC292 and NC330 from B73 and which may contribute to NC292 and NC330s enhanced SLB resistance were identified. Ten NC250P-derived introgressions were identified in both the NC292 and NC330 genomes of which eight were shared between genomes. dQTL were mapped in two F_2:3 populations derived from lines very closely related to the original parents of NC292 and NC330—(B73rhm1 × NC250A and NC250A × B73). Nine SLB dQTL were mapped in the combined populations using combined SLB disease data over all locations (SLB AllLocs). Of these, four dQTL precisely colocalized with NC250P introgressions in bins 2.05–2.06, 3.03, 6.01, and 9.02 and three were identified near NC250P introgressions in bins 1.09, 5.05–5.06, and 10.03. Therefore the breeding program used to develop NC292 and NC330 was highly effective in selecting for multiple SLB resistance alleles. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Characterization and fine-mapping of a resistance locus for northern leaf blight in maize bin 8.06

As part of a larger effort to capture diverse alleles at a set of loci associated with disease resistance in maize, DK888, a hybrid known to possess resistance to multiple diseases, was used as a donor in constructing near-isogenic lines (NILs). A NIL pair contrasting for resistance to northern leaf blight (NLB), caused by Setosphaeria turcica, was identified and associated with bin 8.06. This region of the maize genome had been associated in previous studies with both qualitative and quantitative resistance to NLB. In addition, bins 8.05–8.06 had been associated with quantitative resistance to several other diseases, as well as resistance gene analogs and defense response gene homologs. To test the hypothesis that the DK888 allele at bin 8.06 (designated qNLB8.06 _DK888 ) conditions the broad-spectrum quantitative resistance characteristic of the donor, the NILs were evaluated with a range of maize pathogens and different races of S. turcica. The results revealed that qNLB8.06 _DK888 confers race-specific resistance exclusively to NLB. Allelism analysis suggested that qNLB8.06 _DK888 is identical, allelic, or closely linked and functionally related to Ht2. The resistance conditioned by qNLB8.06 was incompletely dominant and varied in effectiveness depending upon allele and/or genetic background. High-resolution breakpoint analysis, using ~2,800 individuals in F₉/F₁₀ heterogeneous inbred families and 98 F₁₀/F₁₁ fixed lines carrying various recombinant events, delimited qNLB8.06 _DK888 to a region of ~0.46 Mb, spanning 143.92–144.38 Mb on the B73 physical map. Three compelling candidate genes were identified in this region. Isolation of the gene(s) will contribute to better understanding of this complex locus.     

Evaluation of fall armyworm resistance in maize germplasm lines using visual leaf injury rating and predator survey

After examining ear-colonizing pest resistance, 20 maize lines from the USDA- ARS Germplasm Enhancement of Maize （GEM） Program were evaluated for whorl-feeding fall armyworm （FAW） （Spodopterafrugiperda） resistance using 4 maize inbred lines as the resistant and susceptible controls. Both FAW injury ratings at 7- and 14-d after infestation, and predator abundance and diversity at whorl stage （V6-V8） were recorded in 2009 and 2010. The survey of the diversity and abundance of predators in each experimental plot were conducted 7 d after the FAW infestation. Of the 20 germplasm lines examined, 3 of them （i.e., entries 9, 15, and 19 that were derived from tropical maize germplasm lines were originated from Uruguay, Cuba, and Thailand, respectively） were identified as the best FAW-resistant germplasm lines using the leaf injury ratings and predator survey data. In addition, the abundance and diversity of the predators were greater in 2010 than in 2009, which might have caused the low level of the FAW injury ratings on all lines examined in 2010. The 2-year data showed that the FAW injury ratings were negatively correlated to the predator abundance and diversity, which is also influence by genotype × environment interactions. The findings suggested that tropical germplasm is an important source of native resistance to the FAW and the corn earworm. At the same time, the maize genotype x environment interaction （e.g., predator attractiveness, and varying weather conditions） should be included in the multiple-year evaluations of insect and disease resistance of maize germplasm lines under field conditions.     

Genetics of leaf blight resistance in wheat

Summary Studies on the genetics of leaf blight caused byAlternaria triticina using generation mean analysis revealed that additive components played a major role, but that dominance components also contributed significantly in controlling the variability for leaf blight resistance in wheat crosses. Furthermore, the additive x additive type of epistasis was predominant in the first three crosses, whereas in the fourth cross additive x dominance (j) and dominance x dominance (1) components of epistasis were most significant. Because of this it may be desirable to follow a simple recurrent selection scheme for higher tolerance, to isolate resistant plants from the segregating populations derived from crosses of parents of diverse origin following the pedigree method of breeding. CPAN-1887 was very tolerant to leaf blight in the present study and should be utilized in hybridization programs to develop leaf-blight-resistant varieties.     

Dissecting quantitative resistance against blast disease using heterogeneous inbred family lines in rice

SHZ-2 is an indica rice cultivar that exhibits broad-spectrum resistance to rice blast; it is widely used as a resistance donor in breeding programs. To dissect the QTL responsible for broad-spectrum blast resistance, we crossed SHZ-2 to TXZ-13, a blast susceptible indica variety, to produce 244 BC₄F₃ lines. These lines were evaluated for blast resistance in greenhouse and field conditions. Chromosomal introgressions from SHZ-2 into the TXZ-13 genome were identified using a single feature polymorphism microarray, SSR markers and gene-specific primers. Segregation analysis of the BC₄F₃ population indicated that three regions on chromosomes 2, 6, and 9, designated as qBR2.1, qBR6.1, and qBR9.1, respectively, was associated with blast resistance and contributed 16.2, 14.9, and 22.3%, respectively, to the phenotypic variance of diseased leaf area (DLA). We further narrowed the three QTL regions using pairs of sister lines extracted from heterogeneous inbred families (HIF). Pairwise comparison of these lines enabled the determination of the relative contributions of individual QTL. The qBR9.1 conferred strong resistance, whereas qBR2.1 or qBR6.1 individually did not reduce disease under field conditions. However, when qBR2.1 and qBR6.1 were combined, they reduced disease by 19.5%, suggesting that small effect QTLs contribute to reduction of epidemics. The qBR6.1 and qBR9.1 regions contain nucleotide-binding sites and leucine rich repeats (NBS-LRR) sequences, whereas the qBR2.1 did not. In the qBR6.1 region, the patterns of expression of adjacent NBS-LRR genes were consistent in backcross generations and correlated with blast resistance, supporting the hypothesis that multiple resistance genes within a QTL region can contribute to non-race-specific quantitative resistance.     

Characterization of heterotic quantitative trait loci in maize by evaluation of near-isogenic lines and their crosses at two competition levels

In a previous study on a maize (Zea mays L.) population of recombinant inbreds derived from B73 × H99, we identified several quantitative trait loci (QTL) for agronomic traits with high dominance-additive ratio. Then, for four of these QTL, we developed families of near-isogenic lines (NILs) homozygous either for the QTL allele from B73 (BB) or from H99 (HH); for two of these QTL, the NILs’ families were produced in two different genetic backgrounds. The present study was conducted to: (1) characterize these QTL for agronomic traits and (2) verify whether their effects were influenced by the genetic background, inbreeding level and plant density (PD). The six NILs’ families were tested across 3 years and in three experiments at different inbreeding levels as NILs per se and their reciprocal crosses (Experiment 1), NILs crossed to related inbreds B73 and H99 (Experiment 2) and NILs crossed to four unrelated inbreds (Experiment 3). Experiment 2 was conducted at two PDs (4.5 and 9.0 plants m⁻²). Results of Experiments 1 and 2 confirmed previous findings as to QTL effects, with dominance–additive ratio superior to 1 for several traits; as a tendency, dominance effects were more pronounced in Experiment 1. The QTL effects were also confirmed in Experiment 3. The interactions involving QTL effects, families and PD were generally negligible, suggesting a certain stability of the QTL. Results emphasize the importance of dominance effects for these QTL, suggesting that they might deserve further studies, using the NILs’ families and their crosses as base materials.