Genetic and environmental control of dormancy in white-grained wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Grain dormancy in wheat is an important component of resistance to preharvest sprouting and hence an important trait for wheat breeders. The significant influence of environment on the dormancy phenotype makes this trait an obvious target for marker-assisted-selection. Closely related breeding lines, SUN325B and QT7475, containing a major dormancy QTL derived from AUS1408 located on chromosome 4A, but substantially different in dormancy phenotype, were compared with a non-dormant cultivar, Hartog, in a range of controlled environments. As temperature increased, dormancy at harvest-ripeness decreased particularly for QT7475. The dormancy phenotypes of reciprocal F₁ grains involving all possible combinations of Hartog, QT7475 and SUN325B were also compared in two environments with different temperatures. The results were consistent with the presence of QTL in addition to 4A in SUN325B, compared with QT7475, at least one of which was associated with the seed coat. Genetic analysis of a doubled haploid population derived from SUN325B × QT7475 identified a highly significant QTL located on chromosome 3BL, close to the expected position of the mutant allele of the red seed coat colour gene in white-grained wheat, R-B1a. When the lines in the population were grouped according to the parental alleles at marker loci flanking the 3B QTL, the dormancy phenotype frequency distribution for the SUN325B group was shifted towards greater dormancy compared with the QT7475 group. However, significant variation for dormancy phenotype remained within each group. Lines representing the extremes of the range of phenotypes within each group maintained their relative ranking across seven environments consistent with the presence of another unidentified QTL contributing to dormancy in SUN325B.     

QTL analysis for thousand-grain weight under terminal drought stress in bread wheat (<Emphasis Type="Italic">Triticum</Emphasis><Emphasis Type="Italic">aestivum</Emphasis> L.)

Grain yield under post-anthesis drought stress is one of the most complex traits, which is inherited quantitatively. The present study was conducted to identify genes determining post-anthesis drought stress tolerance in bread wheat through Quantitative Trait Loci (QTLs) analysis. Two cultivated bread wheat accessions were selected as parental lines. Population phenotyping was carried out on 133 F_2:3 families. Two field experiments and two experiments in the greenhouse were conducted at IPK-Gatersleben, Germany with control and post-anthesis stress conditions in each experiment. Thousand-grain weight was recorded as the main wheat yield component, which is reduced by post-anthesis drought stress. Chemical desiccation was applied in three experiments as simulator of post-anthesis drought stress whereas water stress was applied in one greenhouse experiment. Analysis of variance showed significant differences among the F_2:3 families. The molecular genetic linkage map including 293 marker loci associated to 19 wheat chromosomes was applied for QTL analysis. The present study revealed four and six QTLs for thousand-grain weight under control and stress conditions, respectively. Only one QTL on chromosome 4BL was common for both conditions. Five QTLs on chromosomes 1AL, 4AL, 7AS, and 7DS were found to be specific to the stress condition. Both parents contributed alleles for drought tolerance. Taking the known reciprocal translocation of chromosomes 4AL/7BS into account, the importance of the short arms of homoeologous group 7 is confirmed for drought stress.     

QTL mapping for developmental behavior of plant height in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

A recombinant inbred line (RIL) population with 305 lines derived from a cross of Hanxuan 10 × Lumai 14 was used to identify the dynamic quantitative trait loci (QTL) for plant height (PH) in wheat (Triticum aestivum L.). Plant heights of RILs were measured at five stages in three environments. Total of seven genomic regions covering PH QTL clusters on different chromosomes identified from a DH population derived from the same cross as the RIL were used as the candidate QTLs and extensively analyzed. Five additive QTLs and eight pairs of epistatic QTLs significantly affecting plant height development were detected by unconditional QTL mapping method. Six additive QTLs and four pairs of epistatic QTLs were identified using conditional mapping approach. Among them, three additive QTLs (QPh.cgb-1B.3, QPh.cgb-4D.1, QPh.cgb-5B.2) and three pairs of epistatic QTLs (QPh.cgb-1B.1–QPh.cgb-1B.3, QPh.cgb-2A.1–QPh.cgb-2D.1, QPh.cgb-2D.1–QPh.cgb-5B.2) were common QTLs detected by both methods. Three QTLs (QPh.cgb-4D.1, QPh.cgb-5B.3, QPh.cgb-5B.4) were expressed under both drought and well-water conditions. The present data are useful for wheat genetic manipulations through molecular marker-assisted selection (MAS), and provides new insights into understanding the genetic mechanism and regulation network underlying the development of plant height in crops. Our result in this study indicated that combining unconditional and conditional mapping methods could make it possible to reveal not only the stable/conserved QTLs for the developmental traits such as plant height but also the dynamic expression feature of the QTLs.     

Grain dormancy in fixed lines of white-grained wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) grown under controlled environmental conditions

Pre-harvest sprouting (PHS) in wheat (Triticum aestivum L.) can be a significant problem, causing deleterious effects on grain quality. However, the adverse impacts of PHS can be reduced by introgressing genes controlling grain dormancy into white-grained bread wheat. Screening for grain dormancy typically involves germination testing of harvest-ripe grain grown in a glasshouse or field. However, the more uniform environmental conditions provided by temperature controlled glasshouses (i.e. controlled environmental conditions—CEC) may provide significant benefits for the assessment of grain dormancy. In this study, the dormancy phenotype of grain grown under CEC incorporating an extended photoperiod, was compared with 2 years of data from field grown material. Four dormant double haploid lines (derived from SW95-50213 and AUS1408) and two locally adapted non-dormant cultivars EGA Gregory and EGA Wills were compared in three replicated experiments grown under CEC (22 ± 3°C and 24 h photoperiod). The germination response of harvest-ripe grain was examined to assess the expression of grain dormancy. Two measures of germination, the predicted time to 50% germination (G ₅₀) and a weighted germination index, both clearly differentiated dormant and non-dormant lines grown under CEC. In addition, levels of grain dormancy were similar to field-grown plants. These results demonstrated that CEC with an extended photoperiod can be used for rapid and reliable characterisation of grain dormancy in fixed lines of bread wheat.     

Germination characters and early seedling growth of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) genotypes under salt stress conditions

Screening of wheat genotypes as salt tolerance through seed germination and early seedling growth is crucial for their evaluation. Seeds of 20 wheat genotypes were germinated in Petri dishes on a sand bed irrigated with saline (15 dS m_-1) and control solutions for 10 days and also tested at different salinity levels (control, 4, 6, 8, and 10 dS m^-1) which were artificially developed in the soil for 30 days. At 10 days, germination percentage, rate of germination, co-efficient of germination, germination vigor index, shoot length, root length, and seedling dry weight were found to be affected due to salinity. Salt tolerance index (STI) for seedling dry weight maintained a significant positive correlation with rate of germination, germination vigor index, shoot length, and root length, which indicates that these parameters could be used as selection criteria for screening wheat genotypes against salt stress. Significant differences in shoot length, root length, and seedling dry weight in 30-day-old seedlings were observed among selected wheat genotypes as well. From the overall observation of germination characters and early seedling growth, it was concluded that the wheat genotypes including Gourab, Shatabdi, Bijoy, Prodip, BARI Gom 26, BAW 1186, and BAW 1189 showed better salt tolerance as compared to others.     

Effects of genotype and environment on N uptake and N partition in organically grown winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) in Germany

Differences among six winter wheat varieties regarding N efficiency (NE) and its components were assessed in field trials in four locations over 3 years under conditions of organic farming (OF). N uptake and utilization efficiency, redistribution of N vs. direct N uptake during grain filling, N uptake in three periods (tillering, stem elongation/heading and grain filling) and the quantity of mineralized N during the same sub-periods were determined. Significant differences for these traits and significant interactions among varieties and environments could be detected for NE and its components. Limiting N availability during grain filling was typical for the more extensive organic environments. Under these conditions, differences of NE could be attributed to differences in pre-anthesis uptake and in translocation from vegetative tissues to the developing grain. Pre-anthesis uptake contributed more to N efficiency than translocation efficiency. Under more favourable conditions, differences became more evident and were mainly due to direct uptake during grain filling. This confirms, that different varieties are necessary in different environments and that breeding may contribute to improve baking quality to a certain extent. However, utilization of mineralized N is still unsatisfactory in OF systems in Germany. More N efficient varieties alone will help only little to resolve this problem; this can be achieved only by also improving the cropping systems.     

Mapping the <Emphasis Type="Italic">compactum</Emphasis> locus in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) and its relationship to other spike morphology genes of the Triticeae

The spikes of club wheat are significantly more compact than spikes of common wheat due to the action of the dominant allele of the compactum (C) locus. Little is known about the location of C on chromosome 2D and the relationship between C and to other spike-compacting genes. Thus, a study was undertaken to place C on linkage maps and a chromosome deletion bin, and to assess its relatedness to the spike compacting genes zeocriton (Zeo) from barley and soft glume (Sog) from T. monococcum. Genetic mapping was based on recombinant inbred lines (RILs) from a cross between the cultivars Coda (club) and Brundage (common) and F₂ progeny from a cross between the club wheat Corrigin and a chromosome 2D substitution line [Chinese Spring (Ae. tauschii 2D)]. The C locus was flanked by Xwmc144 and Xwmc18 in the RIL population and it was completely linked to Xcfd116, Xgwm358 and Xcfd17 in the F₂ population. C could not be unambiguously placed to a chromosome bin because markers that were completely linked to C or flanked this locus were localized to chromosome bins on either side of the centromere (C-2DS1 and C-2DL3). Since C has been cytogenetically mapped to the long arm of chromosome 2D, we suspect C is located in bin C-2DL3. Comparative mapping suggested that C and Sog were present in homoeologous regions on chromosomes 2D and 2A^m, respectively. On the other hand, C and Zeo, on chromosome 2H, did not appear to be orthologous.     

QTL associated with heat susceptibility index in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) under short-term reproductive stage heat stress

Heat stress adversely affects wheat production in many regions of the world and is particularly detrimental during reproductive development and grain-filling. The objective of this study was to identify quantitative trait loci (QTL) associated with heat susceptibility index (HSI) of yield components in response to a short-term heat shock during early grain-filling in wheat. The HSI was used as an indicator of yield stability and a proxy for heat tolerance. A recombinant inbred line (RIL) population derived from the heat tolerant cultivar ‘Halberd’ and heat sensitive cultivar ‘Cutter’ was evaluated for heat tolerance over 2 years in a controlled environment. The RILs and parental lines were grown in the greenhouse and at 10 days after pollination (DAP) half the plants for each RIL received a three-day heat stress treatment at 38°C/18°C day/night, while half were kept at control conditions of 20°C/18°C day/night. At maturity, the main spike was harvested and used to determine yield components. A significant treatment effect was observed for most yield components and a HSI was calculated for individual components and used for QTL mapping. QTL analysis identified 15 and 12 QTL associated with HSI in 2005 and 2006, respectively. Five QTL regions were detected in both years, including QTL on chromosomes 1A, 2A, 2B, and 3B. These same regions were commonly associated with QTL for flag leaf length, width, and visual wax content, but not with days to flowering. Pleiotropic trade-offs between the maintenance of kernel number versus increasing single kernel weight under heat stress were present at some QTL regions. The results of this study validate the use of the main spike for detection of QTL for heat tolerance and identify genomic regions associated with improved heat tolerance that can be targeted for future studies.     

Genetic loci linking improved heat tolerance in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) to lower leaf and spike temperatures under controlled conditions

Heat stress adversely affects wheat production in many regions of the world and is particularly detrimental during reproductive development. The objective of this study was to identify novel quantitative trait loci (QTL) associated with improved heat tolerance in wheat (Triticum aestivum L.) and to confirm previous QTL results. To accomplish this, a recombinant inbred line (RIL) population was subjected to a three-day 38°C daytime heat stress treatment during early grain-filling. At maturity, a heat susceptibility index (HSI) was calculated from the reduction of three main spike yield components; kernel number, total kernel weight, and single kernel weight. The HSI, as well as temperature depression (TD) of the main spike and main flag leaf during heat stress were used as phenotypic measures of heat tolerance. QTL analysis identified 14 QTL for HSI, with individual QTL explaining from 4.5 to 19.3% of the phenotypic variance. Seven of these QTL co-localized for both TD and HSI. At all seven loci, the allele for a cooler flag leaf or spike temperature (up to 0.81°C) was associated with greater heat tolerance, indicated by a lower HSI. In a comparison to previous QTL results in a RIL population utilizing the same source of heat tolerance, seven genome regions for heat tolerance were consistently detected across populations. The genetic effect of combining three of these QTL, located on chromosomes 1B, 5A, and 6D, demonstrate the potential benefit of selecting for multiple heat tolerance alleles simultaneously. The genome regions identified in this study serve as potential target regions for fine-mapping and development of molecular markers for more rapid development of heat tolerant germplasm.     

Cytogenetic Diversity of Korean Hexaploid Wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) with Simple Sequence Repeats (SSRs) by Fluorescence <Emphasis Type="Italic">In Situ</Emphasis> Hybridization

Chromosomes of Korean hexaploid wheat were investigated to compare the chromosomal karyotype for cytogenetic diversity. Chromosomal karyotyping was done with in situ hybridization using two types of simple sequence repeats (SSR)s, (AAG)₅ and (AAC)₅ labeled with tetramethyl-rhodamine-5-dUTP and fluorescein-12-dUPT as a fluorescence, respectively. The two SSRs as cytogenetic markers revealed that the cytogenetic characteristics of the wheat chromosomes were remarkably a B genome. In this study, the chromosomal karyotype of Keumkang, a Korean hexaploid wheat cultivar, was the A, B, and D genomes used as a cytogenetic reference. The expressed signals from the two SSRs showed a difference in the chromosomal karyotype of chromosome 1B among the Korean hexaploid wheat. The distribution pattern and the degree of condensation for the (AAG)₅ and (AAC)₅ signals on the short arm of chromosome 1B were different in the Korean hexaploid wheat shown in descending order: Keumkang > Joeun > Johan > Olgeuru. Olgeuru had a lower level of distribution and condensation for the two SSRs signals compared to the other Korean hexaploid wheat. In the A genome, chromosome 7A showed an unbalanced expression of the (AAG)₅ signal on the distal region of the short and long arms in several Korean hexaploid wheat while Joeun, a Korean hexaploid wheat, showed a definite (AAG)₅ signal on the distal region of each arm of chromosome 7A. Among the Korean hexaploid wheat, Shinmichal1, a Korean hexaploid waxy wheat, had a chromosome with a unique expression pattern for (AAG)₅ and (AAC)₅ compared the other Korean hexaploid wheat. Those cytogenetic differences identified in this study are useful as an indicator to improve the cytogenetic diversity in the Korean wheat breeding program.     

An approach to DNA polymorphism screening in <Emphasis Type="Italic">SBEIIa</Emphasis> homeologous genes of polyploid wheat (<Emphasis Type="Italic">Triticum</Emphasis> L.)

The non-transgenic manipulation of starch properties in common wheat (Triticum aestivum L.) generally implies combining mutant alleles of the particular gene copies in all three subgenomes (A, B and D). The redundancy of the hexaploid wheat chromosome set substantially complicates the identification of recessive mutations and breeding. Nevertheless, naturally occurring or induced genetic polymorphism has already been successfully exploited for the production of waxy (GBSSI-deficient) and elevated amylose (SSIIa-deficient) wheats. However, in order to achieve the amylose content above 50% of wheat endosperm starch, it may be necessary to inactivate the starch branching enzyme (SBEIIa) isoforms, as the RNAi repression results and gene expression data strongly suggest. The identification of null SBEIIa alleles and their combination in a single genotype is therefore a promising approach to the production of non-transgenic high-amylose wheat; however, wheat SBEIIa polymorphism has not been characterized as of yet. In order to develop an approach to SBEIIa mutation screening, we sequenced the SBEIIa central region (exons 9–12) from the three subgenomes of common wheat cv. Chinese Spring and the A genome of diploid einkorn T. monococcum. The genome-specific primers were developed that amplify the exons downstream from intron 11 selectively from each homeologous gene. Using a single-stranded DNA conformation polymorphism (SSCP) approach, we screened 60 wheat cultivars, landraces, and rare species for naturally occurring SNPs in exons 12, 13 and 14 of the three SBEIIa homeologs. In total, 13 SNPs were discovered in the A and B wheat genomes. Two of these SNPs affect the amino acid sequences of SBEIIa isoforms and may change the enzyme functional properties. The presence of restriction site polymorphism at SNP positions enables their easy genotyping with CAPS assays. Our results indicate that the mining for naturally occurring sequence polymorphism in starch biosynthesis genes of wheat can be successfully performed at the DNA level, providing the starting point for a search for SBEIIa mutants at a larger scale.     

A simple,rapid and reliable bioassay for evaluating seedling vigor under submergence in <Emphasis Type="Italic">indica</Emphasis> and <Emphasis Type="Italic">japonica</Emphasis> rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Submergence is a major stress causing yield losses particularly in the direct-seeded rice cultivation system and necessitates the development of a simple, rapid and reliable bioassay for a large scale screening of rice germplasms with tolerance against submergence stress. We developed two new bioassay methods that were based primarily on the seedling vigor evaluated by the ability of fast shoot elongation under submerged conditions, and compared their effectiveness with two other available methods. All four bioassay methods using cultivars of 7 indica and 6 japonica types revealed significant and consistent cultivar differences in seedling vigor under submergence and/or submergence tolerance. Japonica cultivars were more vigorous than indica cultivars, with Nipponbare being the most vigorous. The simplest test tube method showed the highest correlations to all other methods. Our results suggest that seedling vigor serves as a submergence avoidance mechanism and confers tolerance on rice seedlings to flooding during early crop establishment. A possible relationship is discussed between seedling vigor based on fast shoot elongation and submergence tolerance defined by recovery from submergence stress.     

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.     

Positive or negative effects on dough strength in large-scale group-1 chromosome deletion lines of common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

We studied the seed storage protein composition and dough strength of chromosome deletion (CD) lines involving group-1 chromosomes. The presence or absence of genes and protein bands corresponding to glutenin and gliadin was assessed by using locus-specific DNA markers, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and acid-polyacrylamide gel electrophoresis (A-PAGE). In this study, we were able to map the physical positions of several glutenin and gliadin genes in detail. Dough strength was evaluated by SDS sedimentation volume and protein content. We found that protein composition affected dough strength. The absence of chromosome arm 1AL, which carries the truncated glutenin gene Glu-A1c, significantly increased dough strength, although the protein composition did not change when the size of the deleted chromosome region was varied. In contrast, the presence of chromosome arm 1DL, which carries Glu-D1a (the gene for glutenin subunits 2 and 12), significantly increased dough strength. We did not find any known seed storage protein loci in any of the other chromosomal regions that significantly affected dough strength.     

Confirmation of the relationship between plant height and Fusarium head blight resistance in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) by QTL meta-analysis

Fusarium head blight (FHB) is a serious wheat disease all over the world. In this study, the relationships between plant height (PH) and FHB were investigated across the whole wheat genome by QTL meta-analysis from fifty-six experiments. Coincident meta-QTL (MQTL) for PH and FHB were found on chromosomes 2D, 3A, 4B, 4D and 7A. Rht-B1, Rht-D1, Rht8, MQTLs P7 and P26 were consistent with FHB MQTLs. The meta-analysis results confirmed the negative associations of Rht-B1, Rht-D1, and Rht8 with FHB resistance. The associations of PH and FHB resistance on chromosomes 3A and 7A have not been reported and need further investigation. These regions should be given attention in breeding programs. MQTLs derived from several resistance sources were also observed. Some FHB MQTLs for different types of resistance overlapped. These findings could be useful for improving wheat varieties with resistance to FHB.     

Allelic variation and composition of HMW-GS in advanced lines derived from d-genome synthetic hexaploid / bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

The objective of this study was to identify allelic variations at Glu-1 loci of wheat (Triticum aestivum L.) advanced lines derived from hybridization of bread wheat and synthetic hexaploid wheats (2n = 6x = 42; AABBDD). Locally adapted wheat genotypes were crossed with synthetic hexaploid wheats. From the 134 different cross combinations made, 202 F₈ advanced lines were selected and their HMW-GS composition was studied using SDS-PAGE. In total, 24 allelic variants and 68 HMW-GS combinations were observed at Glu-A1, Glu-B1, and Glu-D1 loci. In bread wheat, the Glu-D1 locus is usually characterized by subunits 1Dx2+1Dy12 and 1Dx5+1Dy10 with the latter having a stronger effect on bread-making quality. The subunit 1Dx5+1Dy10 was predominantly observed in these advanced lines. The inferior subunit 1Dx2+1Dy12, predominant in adapted wheat germplasm showed a comparative low frequency in the derived advanced breeding lines. Its successful replacement is due to the other better allelic variants at the Glu-D1 locus inherited in these synthetic hexaploid wheats from Aegilops tauschii (2n = 2x = 14; DD).     

Genetic variation in drought tolerance at seedling stage and grain yield in low rainfall environments in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Genetic architecture of seedling drought tolerance is complex and needs to be better understood. To address this challenge, we developed a protocol to identify the most promising drought-tolerant genotypes at the seedling stage in winter wheat. A population of 146 recombinant inbred lines (F₉) derived from a cross between wheat cultivars, ‘Harry’ (seedling drought tolerant) and ‘Wesley’ (seedling drought susceptible) were used in this study. All genotypes were sown in three replications in a randomized complete block design under controlled conditions in a greenhouse. Seven traits were scored and grouped into tolerance traits; days to wilting, leaf wilting, and stay green and survival traits; days to regrowth, regrowth, drought survival rate, and recovery after irrigation. Three selection indices were calculated (1) tolerance index, (2) survival index, and (3) drought tolerance index (DTI). The same set of genotypes were also tested for grain yield in two low rainfall environments for two seasons. High genetic variation was found among all genotypes for all seedling traits scored in this study. Correlations between tolerance and survival traits were weak or did not exist. Heritability estimates ranged from 0.53 to 0.88. DTI had significant phenotypic and genotypic correlations with all seedling traits. Genotypes were identified with a high drought tolerance at the seedling stage combined with high grain yield in low rainfall. Breeding for tolerance and survival traits should be taken into account for improving winter wheat drought tolerance at seedling stage. The selected genotypes can be used for to further improve drought tolerance in high yielding wheat for Nebraska.     

Genetic effects of introgression genomic components from Sea Island cotton (<Emphasis Type="Italic">Gossypium barbadense</Emphasis> L.) on fiber related traits in upland cotton (<Emphasis Type="Italic">G</Emphasis>. <Emphasis Type="Italic">hirsutum</Emphasis> L.)

The germplasm with exotic genomic components especially from Sea Island cotton (Gossypium barbadense L. Gb) is the dominant genetic resources to enhance fiber quality of upland cotton (G. hirsutum L., Gh). Due to low efficiency of phenotypic evaluation and selection on fiber quality, genetic dissection of favorable alleles using molecular markers is essential. Genetic dissection on putative Gb introgressions related to fiber traits were conducted by SSR markers with mapping populations derived from a cross between Luyuan343 (LY343), a superior fiber quality introgression line (IL) with genomic components from Gb, and an elite Upland cotton cv. Lumianyan#22 (LMY22). Among 82 polymorphic loci screened out from 4050 SSRs, 42 were identified as putative introgression alleles. A total of 29 fiber-related QTLs (23 for fiber quality and six for lint percentage) were detected and most of which clustered on the putative Gb introgression chromosomal segments of Chr.2, Chr.16, Chr.23 and Chr.25. As expected, a majority of favorable alleles of fiber quality QTLs (12/17, not considering the QTLs for fiber fineness) came from the IL parent and most of which (11/12) were conferred by the introgression genomic components while three of the six (3/6) favorable alleles for lint percentage came from the Gh parent. Validation of these QTLs using an F₈ breeding population from the same cross made previously indicated that 13 out of 29 QTLs showed considerable stability. The results suggest that fiber quality improvement using the introgression components could be facilitated by marker-assisted selection in cotton breeding program.     

Inheritance of red foliage in flowering dogwood (<Emphasis Type="Italic">Cornus florida</Emphasis> L.)

Flowering dogwood (Cornus florida L.) is an ornamental tree valued for its showy white, pink, or red spring bract display and red fall color. A “pseudo” F₂ flowering dogwood population was recently developed from a honeybee mediated cross of ‘Cherokee Brave’ × ‘Appalachian Spring’. The foliage color of 94 “pseudo” F₂ plants segregated into green- and red- leaved phenotypes and was visually rated for color on five spring dates over 3 years (2007–2009). Chi-square analyses of observed segregation of phenotypes indicated that a complementary gene interaction form of epistasis controls foliage color with a 9:7 two gene ratio. We propose the symbols rl ₁ and rl ₂ for the genes controlling this trait.     

RDA derived <Emphasis Type="Italic">Oryza minuta</Emphasis>-specific clones to probe genomic conservation across <Emphasis Type="Italic">Oryza</Emphasis> and introgression into rice (<Emphasis Type="Italic">O. sativa</Emphasis> L.)

Molecular markers have been successfully used in rice breeding however available markers based on Oryza sativa sequences are not efficient to monitor alien introgression from distant genomes of Oryza. We developed O. minuta (2n = 48, BBCC)-specific clones comprising of 105 clones (266–715 bp) from the initial library composed of 1,920 clones against O. sativa by representational difference analysis (RDA), a subtractive cloning method and validated through Southern blot hybridization. Chromosomal location of O. minuta-specific clones was identified by hybridization with the genomic DNA of eight monosomic alien additional lines (MAALs). The 37 clones were located either on chromosomes 6, 7, or 12. Different hybridization patterns between O. minuta-specific clones and wild species such as O. punctata, O. officinalis, O. rhizomatis, O. australiensis, and O. ridleyi were observed indicating conservation of the O. minuta fragments across Oryza spp. A highly repetitive clone, OmSC45 hybridized with O. minuta and O. australiensis (EE), and was found in 6,500 and 9,000 copies, respectively, suggesting an independent and exponential amplification of the fragment in both species during the evolution of Oryza. Hybridization of 105 O. minuta specific clones with BB- and CC-genome wild Oryza species resulted in the identification of 4 BB-genome-specific and 14 CC-genome-specific clones. OmSC45 was identified as a fragment of RIRE1, an LTR-retrotransposon. Furthermore this clone was introgressed from O. minuta into the advanced breeding lines of O. sativa.