Molecular Marker-Assisted Dissection of Quantitative Trait Loci for seven Morphological Traits in Rice (Oryza Sativa L.)

Summary The genetic dissection of morphological traits can helpful to evaluate their potential values as markers for rice genetic improvement. In this study, a RI population derived from a cross from Zhenshan97 and IRAT109 was used to dissect the genetic bases of seven morphological traits such as leaf sheath color (LSC), grain apiculus color (GAC), grain hairiness density (GHD), grain awn length (GAL), ratio of leaf length to width (RLW), leaf erectness (LER) and natural leaf rolling status (NLR). Totally, 26 main-effect QTLs and 22 epistatic QTLs were detected. Of them, 11 main-effect and 3 epistatic QTLs expressed environmental interactions. GAC controlled by a single gene could be regarded as the most useful marker. LSC controlled by two major interacted main-effect QTLs, but with no environmental interaction, is suitable to become morphological marker. LSC will be a very efficient morphological marker for identification of hybrid plants at rice seedling stage when the two major QTLs are introduced into male sterile line and restorer line separately. GHD controlled by a major QTL and a few minor QTLs with comparative low QEIs could also be used as marker. The traits GAL, NLR, RLW and LER, which were controlled by a number of minor effect QTLs and affected by environmental conditions could not be used as marker. But the QTLs with large effects, such as nrl8, can be targeted for corresponding trait improvement through marker-aided selection in rice breeding.     

Development of synthetic Brassica napus lines for the analysis of “fixed heterosis” in allopolyploid plants

Summary Allopolyploids are widely spread in the plant kingdom. Their success might be explained by positive interactions between homoeologous genes on their different genomes, similar to the positive interactions between different alleles of one gene causing heterosis in heterozygous diploid genotypes. In allopolyploids, such interactions can also occur in homozygous genotypes, and may therefore be called “fixed heterosis”. As to our knowledge, no experimental data are available to support this hypothesis. We propose an experimental approach to quantify “fixed heterosis” in resynthesised Brassica napus and the detection of loci contributing to “fixed heterosis” via comparative QTL mapping in B. napus and its parental species B. rapa and B. oleracea. In order to develop a genetically balanced material, interspecific crosses between 21 Brassica rapa and 16 Brassica oleracea doubled haploid or inbred lines were performed. In total 3485 vital embryos have been obtained from 9514 pollinated buds. The success of interspecific hybridisation was highly depending on the maternal genotype (B. rapa) and ranged from 0 to 1.18 embryos per pollinated bud. For the genetic characterisation of the B. rapa and B. oleracea lines, a dendrogram was constructed based on 273 RAPD markers. Thus a well-characterised material is now available, which is suitable to analyse the effects of “fixed heterosis” and the interactions between homoeologous genes in allopolyploid species.     

Genetics of grain yield and other agronomic characters in t'ef (Eragrostis tef Zucc Trotter). II. The triple test cross

The normal and selfed families of the triple test cross were employed to detect gene action in t'ef for grain yield and other useful agronomic characters in the breeding programme. Cultivars Kay Murri and Fesho were used as L₁ and L₂ testers, respectively. Eight randomly selected cultivars and two released varieties (DZ-01-354 and DZ-01-196) were crossed with the testers L₁, L₂ and L₃ (the F₁ of L₁ × L₂). In the case of the selfed families, 14 cultivars and two released varieties were used for crossing with the testers. The normal families were grown on an Inceptisol developed from volcanic ash whilst the selfed families were grown on a pellic Vertisol at the Debre Zeit Agricultural Research Centre, Ethiopia. The rainfall during the experimental season was 463 mm. Epistasis was detected for grain yield, yield per panicle, panicle weight, plant weight, harvest index, tiller number, panicle length, culm diameter, days to heading and days to maturity in the normal families of the triple test cross (TTC) of t'ef. Similarly the characters grain yield, yield per panicle, panicle weight, plant height, panicle length, days to heading and days to maturity showed epistasis in the selfed families of the TTC. Epistatic interaction was not important for shoot biomass and for harvest index (for the transformed data) in this family. Therefore, both the normal and selfed families of the TTC were in agreement with regard to detecting epistasis for grain yield, yield per panicle, panicle weight, panicle length, days to heading and days to maturity. Significant additive (D) and dominance (H) components were estimated for the characters in both families, although the magnitudes might have been inflated due to epistasis. The dominance component for panicle length was unimportant in both families of the TTC and as a result the additive components were not biased. In general, the additive, dominance and epistatic components were important in t'ef. Since the crop is self-fertilized only the additive and additive × additive terms are important to develop pure breeding varieties. Therefore, selection for superior segregants should start in advanced generations as homozygosity increases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic basis of the evolution of adaptedness in plants

Summary Adaptedness is both complexly inherited and much affected by environment: consequently the genetic mechanisms that have led to improvements in adaptedness have been difficult to identify and to quantify. Recently it has been shown that marker assisted dissection of adaptedness based on changes in the frequencies of discretely inherited alleles of loci of various kinds (e.g. allozyme, restriction fragment, microsatellite loci) is practicable. I will illustrate marker assisted analysis of the genetic basis of adaptedness with a sample of allozyme data from three species groups, two heavily selfing groups (two wild Avena species and barley) and one outcrossing species (corn, maize). The results lead to three main conclusions: (1) that the single most important genetic mechanism in all three species groups was the assembly of favorable epistatic combinations of alleles of different loci by means of recurring cycles of selection, intercrossing superior selects, and inbreeding to near homozygosity leading to stable superior multilocus genotypes adapted to specific habitats; (2) that exploitation of favorable interactions among alleles of the same locus played a significant role in tetraploid A. barbata and probably also in single-cross maize hybrids; (3) that purifying selection (elimination of deleterious alleles) played a small role in all three species groups. These results indicate that marker alleles provide applied breeders with effective ways to identify, track, and incorporate regions of chromosomes with favorable effects of adaptedness into improved cultivars.     

The inheritance and association of resistance to rust,common bacterial blight,plant habit and foliar abnormalities in Phaseolus vulgaris L.

Summary No antagonistic or synergistic interaction was found between isolates of Uromyces appendiculatus var. appendiculatus and Xanthomonas campestris pv. phaseoli when inoculated to the same plant. A single dominant gene was suggested to control resistance to three isolates of rust in the crosses Pompadour Checa × Chichara and Pompadour Checa × NE W-4. A two-gene model was confirmed for the reaction to the three rust isolates for the crosses Pompadour Checa × GN Tara and Pompadour Checa × San Cristobal; a dominant (Ur _p) gene determined resistance and was epistastic to a dominant gene (Ur _t) for susceptibility. (Ur _t) was expressed only in the presence of recessive (ur _p) alleles. The reaction to common bacterial blight was quantitatively inherited and an association was detected with plant habit but not with rust reaction and leaf variegation. Plants with leaf variegation and crippled growth, were detected in the progeny of the cross Pompadour Checa × GN Tara and were controlled by duplicate recessive genes (mutatorunstable genes) and three genes, acting additively, respectively. The developmental expression of the latter trait varied considerably. Linkage was detected between genes controlling the variegated and the crippling traits.Published as Paper No. 7839, Journal Series, Nebraska Agricultural Experiment Station. Research was conducted under project No. 20-036.     

Present and future of quantitative trait locus analysis in plant breeding

The joint analysis of genotype marker segregation and phenotypic values of individuals or lines enables the detection and location of loci affecting quantitative traits (QTL). The availability of DNA markers and powerful biometric methods has led to considerable progress in QTL mapping in plants. The most obvious applications of QTL analysis seem to be marker‐assisted selection (MAS) in breeding and pre‐breeding and QTL cloning. However, other areas are envisaged where QTL analysis can contribute decisively. These are: the understanding of complex traits such as plant‐pathogen interaction; plant genomics, connecting proteins and regulatory elements of known functions to QTL by candidate gene analysis; and germplasm enhancement through a characterization that allows its efficient utilization. The success in all these applications depends primarily on the reliability and accuracy of the QTL analysis itself. Therefore, the discussion of its limitations will constitute an important part of this review.     

Additive and epistatic effects of allelic variation at the high molecular weight glutenin subunit loci in determining the bread-making quality of breeding lines of wheat

Summary The relation has been studied between the high molecular weight glutenin (HMWg) subunit alleles and the bread-making quality of 226 lines of winter wheat (T. aestivum L.), grown in The Netherlands. The lines represented a wide range of genetic backgrounds, and had not been selected for quality, in contrast to the established varieties used by other authors.The variation in HMWg subunit genotypes accounted for about 20% of the total variation in loaf volume among the lines. Most important was the allelic variation at the Glu-D1 locus. The Glu-D1 allele encoding the subunits 5+10 was superior to its allelic counterpart, encoding 2+12. The difference in average of loaf volume between groups of lines containing 5+10 or 2+12 was negatively related with protein content of the flours. When protein content was below 9.2%, no effect of allelic variation at the Glu-D1 locus was present. Epistatic effects between the Glu-I loci also contributed to the variation in loaf volume of the lines: i.e. the effect of allelic variation at Glu-A1 and Glu-B1 depended on the allele present at the Glu-D1. The contribution of the epistatic effects was about half the contribution of the additive effects, and should therefore be included in predictive models for bread-making quality.     

The cell biology of plant transformation: Current state,problems, prospects and the implications for the plant breeding

Summary The DNA delivery systems which are routinely used to introduce genes into crop plants are Agrobacterium tumefaciens, electroporation and particle bombardment. The differences and similarities between these different transformation techniques are outlined. The influence of the cell biological approach, and more specifically the impact of the state of the plant cell at the moment of transformation, on the genotype and phenotype of the regenerated transgenic plant is analysed. In this respect phenomena such as position effects, gene silencing, co-suppression, epistasis, co-transformation and somaclonal variation are discussed. The relevance of these factors for plant breeders is discussed.     

Heterosis and epistasis in rapeseed estimated from generation means

Summary Heterosis and epistasis in spring oilseed rape (Brassica napus L.) was analysed by comparing generation means for ten agronomic traits. Parents, F₂, F₃ and F₆ generations of four crosses with Swedish and French material were investigated. The F₂ was 11% higher in yield, earlier in flowering time, and slightly later in maturation when compared with the parents. Randomly derived single seed descent lines had an 8% lower yield, were later flowering and maturing than the parents in F₆. This poorer average performance of recombinant lines is explained by the loss of favourable epistatic interactions present in the parents.     

水稻苗期耐高Cu2+胁迫的QTL定位和上位性分析

用珍汕97B/密阳46构建RIL群体及其遗传图谱,对其种子采用沙培法育苗和培养,试验设置2个高浓度(100.mg/L和200.mg/L)Cu2+胁迫处理,以处理20.d后的幼苗相对根长(%)和相对苗高(%)作为苗期耐Cu2+胁迫指标,并用于QTL定位分析。结果表明,试验共检测到苗期耐Cu2+胁迫的主效应QTL.4个,以相对根长为指标,检测到qRCC(r)6(100.mg/L)和qRCC(r)9(200.mg/L),以相对苗高为指标,也检测到qRCC(s)1-2(100.mg/L和200mg/L)和qRCC(r)6-1(200.mg/L),有效基因分散于双亲中。试验还检测到苗期耐Cu2+胁迫的上位性互作8对,以相对根长为指标时,检测到2对互作;以相对苗高为指标时,检测到6对上位性互作。表明水稻苗期耐高浓度Cu2+胁迫,其上位性互作也起到较为重要作用。