Detection of quantitative trait loci for agronomic, yield, grain and disease characters in spring barley (Hordeum vulgare L.).

Quantitative trait loci (QTLs) have been revealed for characters in a segregating population from a spring barley cross between genotypes adapted to North-West Europe. Transgressive segregation was found for all the characters, which was confirmed by the regular detection of positive and negative QTLs from both parents. A QTL for all the agronomic, yield and grain characters measured except thousand grain weight was found in the region of the denso dwarfing gene locus. There were considerable differences between the location of QTLs found in the present study and those found in previous studies of North American germ plasm, revealing the diversity between the two gene pools. Thirty-one QTLs were detected in more than one environment for the 13 characters studied, although many more were detected in just one environment. Whilst biometrical analyses suggested the presence of epistasis in the genetic control of some characters, there was little evidence of interactions between the QTLs apart from those associated with yield. QTLs of large effect sometimes masked the presence of QTLs of smaller effect.

Molecular mapping of genes determining height, time to heading, and growth habit in barley (Hordeum vulgare).

A combination of random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers has been used to locate genes controlling important developmental characters in barley. The denso dwarfing gene has been mapped to the long arm of chromosome 3H. Stepwise multiple regression was also used to identify another region of the barley genome (on chromosome 7H), which contributed to variation in height. The denso locus was shown to be associated with delaying time to heading. A protein (WSP2) and an RAPD marker on barley chromosomes 5H and 6H, respectively, were also associated with time to heading. These results are discussed in relation to the genetic analysis of developmentally important traits and the development of dwarfing genes in barley breeding programs.

Identification of RAPD markers linked to a Rhynchosporium secalis resistance locus in barley using near-isogenic lines and bulked segregant analysis.

Three hundred random sequence 10-mer primers were used to screen a pair of near-isogenic lines of barley and their donor parent for markers linked to genes conferring resistance to Rhynchosporium secalis. One primer was identified which reproducibly generated a product, SC10-65-H400, from the donor parent and the Rhynchosporium-resistant near-isogenic line but not from the recurrent parent. Segregation analysis on a barley doubled haploid population and examination of a further three near-isogenic lines, their donor and recurrent parents confirmed that this marker was linked to the Rhynchosporium resistance locus (Rh) on chromosome 3L. The presence or absence of SC10-65-H400 was subsequently used along with the resistance phenotype to identify two groups of individuals in the doubled haploid population which possessed alternative alleles at both loci and defined a genetic interval between these two markers. Based on that information two bulked DNA samples were constructed by combining equal amounts of DNA from five individuals from each group. The two bulks and doubled haploid parental lines were screened with 700 10-mer primers. Seven products were identified which were present in the 'resistant' bulk and parent and were absent in the susceptible samples. Segregation analysis established their association with Rh. In addition co-segregation of the linked markers with a set of chromosome arm specific RFLPs confirmed the location of the Rh locus on the long arm of barley chromosome 3.

Identification of RAPD markers linked to genetic factors controlling the milling energy requirement of barley.

Doubled haploid (DH) populations of barley have been used in combination with PCR-based polymorphic-assay procedures to identify molecular markers linked to genes controlling the milling energy requirement of the grain. Milling energy (ME) is a quantitative trait and locating individual quantitative trait loci (QTLs) involved the construction of bulks by combining DNA from DH families representing the extreme members of the distribution for ME. In addition, the individuals had alternative alleles at theRrn2 locus that has previously been shown to be linked to an ME QTL. The DNA bulks were screened with Randomly Amplified Polymorphic DNA (RAPD) markers and polymorphic amplification products tested for linkage to genes influencing the expression of ME in a DH population. Several markers were identified which are linked to a QTL controlling ME and the recombination fraction determined by maximum likelihood procedures. The results indicate that DHs in combination with RAPDs and bulked segregant analysis provide an efficient method for locating QTLs in barely. Furthermore, this approach is applicable to mapping other QTLs in a range of organisms from which DH or recombinant inbred lines can be extracted.