Quantitative Trait Loci For Seed Dormancy Research Articles

Detection of loci controlling seed dormancy on group 4 chromosomes of wheat and comparative mapping with rice and barley genomes

Three quantitative trait loci (QTLs) controlling seed dormancy were detected on group 4 chromosomes of wheat (Triticum aestivum L.) using 119 doubled haploid lines (DHLs) derived from a cross between AC Domain and Haruyutaka. A major QTL, designated QPhs.ocs-4A.1, was identified within the marker interval between Xcdo795 and Xpsr115 in the proximal region of the long arm of chromosome 4A. Two minor QTLs, QPhs.ocs-4B.2 on 4B and QPhs.ocs-4D.2 on 4D, were flanked by common markers, Xbcd1431.1 and Xbcd1431.2 in the terminal region of the long arms, suggesting a homoeologous relationship. These three QTLs explained more than 80% of the total phenotypic variance in seed dormancy of DHLs grown in the field and under glasshouse conditions. The AC Domain alleles at the three QTLs contributed to increasing seed dormancy. Comparative maps across wheat, barley and rice demonstrated the possibility of a homoeologous relationship between QPhs.ocs-4A.1 and the barley gene SD4, while no significant effects of the chromosome regions of wheat and barley orthologous to rice chromosome 3 region carrying a major seed dormancy QTL were detected.

Inheritance and fine mapping of a major barley seed dormancy QTL

A major barley seed dormancy locus, SD1, was previously identified along with three others by quantitative trait locus (QTL) analysis in a Steptoe×Morex mapping population. Located in the centromere region of barley chromosome 7 (5H), SD1 shows the largest and most consistent effect on dormancy. Steptoe contributes the dormancy allele at SD1. The objective of this study was to determine the inheritance of and a more precise map location for SD1. A segregating population was designed and generated by marker assisted mating in which only SD1 segregated. The segregation ratio suggested a single Mendelian gene in which the dormancy allele is dominant to the non-dormancy allele at SD1. In addition, near isogenic lines (NIL) for the SD1 chromosome region were generated by molecular marker assisted backcrossing. Statistical analysis of germination percentages of these NIL revealed that there may be a gene cluster of at least three genes in the SD1 locus region. The dormancy locus, presumably SD1 or a part of the SD1 complex, was resolved into a ≈4.4 cM region.

Individual Locus Effects on Dormancy during Seed Development and After Ripening in Barley

Genetic control of seed dormancy in barley (Hordeum vulgare L.) has been studied recently by means of quantitative trait loci (QTL) mapping. Four QTL, designated SDI to SD4, were found associated with about 75% of the phenotypic variation for dormancy in ‘Steptoe’/ ‘Morex’ crosses. The objective of this study was to investigate the individual effects of seed dormancy(SD) QTL and the nature of their epistatic interactions on dormancy during seed development and after ripening. Six F1‐derived doubled haploid lines from Steptoe/Morex crosses, selected on the basis of the flanking marker alleles for the four SD QTL, and the two parents were grown under greenhouse conditions. The same lines and four additional doubled haploid lines from the same cross were also grown in a field experiment. Genotypic dependence of onset, maintenance, and release of dormancy was studied. To assess dormancy, germination tests of excised embryos from fresh and artificially dried seed were conducted during seed development. All genotypes showed a similar pattern of germination of excised embryos. Since no differences in the time of dormancy inception were found, this phenomenon does not seem to be controlled by the SD QTL. Rather, the SD QTL were involved in the release of dormancy at the end of the development process and during after ripening. The presence of the Steptoe allele at SD1 on chromosome 7 (5H) kept precocious germination to a minimum until the end of the seed development process. On the basis of the dormancy profiles at after ripening, genotypes could be classified as affecting early, intermediate, and late dormancy release. These groups were genotypically dependent. A model for allele interactions among the SD QTL was developed.

Mapping quantitative trait loci controlling seed dormancy and heading date in rice, Oryza sativa L., using backcross inbred lines

To detect quantitative trait loci (QTLs) controlling seed dormancy, 98 BC1F5 lines (backcross inbred lines) derived from a backcross of Nipponbare (japonica)/Kasalath (indica)//Nipponbare were analyzed genetically. We used 245 RFLP markers to construct a framework linkage map. Five putative QTLs affecting seed dormancy were detected on chromosomes 3, 5, 7 (two regions) and 8, respectively. Phenotypic variations explained by each QTL ranged from 6.7% to 22.5% and the five putative QTLs explained about 48% of the total phenotypic variation in the BC1F5 lines. Except for those of the QTLs on chromosome 8, the Nipponbare alleles increased the germination rate. Five putative QTLs controlling heading date were detected on chromosomes 2, 3, 4, 6 and 7, respectively. The phenotypic variation explained by each QTL for heading date ranged from 5.7% to 23.4% and the five putative QTLs explained about 52% of the total phenotypic variation. The Nipponbare alleles increased the number of days to heading, except for those of two QTLs on chromosomes 2 and 3. The map location of a putative QTL for heading date coincided with that of a major QTL for seed dormancy on chromosome 3, although two major heading-date QTLs did not coincide with any seed dormancy QTLs detected in this study.