Biomedical subjects

W T Thomas

Publications and source records attributed to W T Thomas.

6 recordsLinked to original sources

PubMed2001

Multi-trait QTL mapping in barley using multivariate regression.

Many studies of QTL locations record several different traits on the same population, but most analyses look at this information on a trait-by-trait basis. In this paper we show how the regression approach to QTL mapping of Haley & Knott (1992) may be extended to a multi-trait analysis via multivariate regression, easily programmed in statistical packages. A procedure for identifying QTL locations using forward selection and bootstrapping is proposed. The method is applied to examine the locations for QTLs for six yield characters (the number of fertile stems, the grain number of the main stem, the main stem grain weight, the single plant yield, the plot yield and the thousand grain weight) in a doubled haploid population of spring barley. Several chromosomal locations with effects on more than one trait are found. The method is also suitable for examining a single trait measured in different years or environments, and is used here to examine data on heading date, a highly heritable trait, and plot yield, a trait with moderate heritability and showing QTL-environment interactions.

Chromosome Mapping↗

PubMed2000

Phenotypic responses of wild barley to experimentally imposed water stress.

Responses to water stress within a population of wild barley from Tabigha, Israel, were examined. The population's distribution spans two soil types: Terra Rossa (TR) and Basalt (B). Seeds were collected from plants along a 100 m transect; 24 genotypes were sampled from TR and 28 from B. Due to different soil water-holding capacities, plants growing on TR naturally experience more intense drought than plants growing on B. In a glasshouse experiment, water was withheld from plants for two periods (10 d and 14 d) after flag leaf emergence. A total of 15 agronomic, morphological, developmental, and fertility related traits were examined by analysis of variance (ANOVA). Ten of these traits were significantly affected by the treatment. A high degree of phenotypic variation was found in the population with significant genotypextreatment and soil typextreatment interactions. Principal component analysis (PCA) was performed using combined control and stress treatment data sets. The first three principal components (pc) explained 88.8% of the variation existing in the population with pc1 (47.9%) comprising yield-related and morphological traits, pc2 (22.9%) developmental characteristics and pc3 (18.0%) fertility-related traits. The relative performance of individual genotypes was determined and water stress tolerant genotypes identified. TR genotypes were significantly less affected by the imposed water stress than B genotypes. Moreover, TR genotypes showed accelerated development under water deficit conditions. Data indicate that specific genotypes demonstrating differential responses may be useful for comparative physiological studies, and that TR genotypes exhibiting yield stability may have value for breeding barley better adapted to drought.

Adaptation, Physiological↗

PubMed2000

The development and application of molecular markers for abiotic stress tolerance in barley.

This article represents some current thinking and objectives in the use of molecular markers to abiotic stress tolerance. Barley has been chosen for study as it is an important crop species, as well as a model for genetic and physiological studies. It is an important crop and, because of its well-studied genetics and physiology, is an excellent candidate in which to devise more efficient breeding methods. Abiotic stress work on cultivated gene pools of small grain cereals frequently shows that adaptive and developmental genes are strongly associated with responses. Developmental genes have strong pleiotropic effects on a number of performance traits, not just abiotic stresses. One concern is that much of the genetic variation for improving abiotic stress tolerance has been lost during domestication, selection and modern breeding, leaving pleiotropic effects of the selected genes for development and adaptation. Such genes are critical in matching cultivars to their target agronomic environment, and since there is little leverage in changing these, other sources of variation may be required. In barley, and many other crops, greater variation to abiotic stresses exists in primitive landraces and related wild species gene pools. Wild barley, Hordeum spontaneum C. Koch is the progenitor of cultivated barley, Hordeum vulgare L. and is easily hybridized to H. vulgare. Genetic fingerprinting of H. spontaneum has revealed genetic marker associations with site-of-origin ecogeographic factors and also experimentally imposed stresses. Genotypes and collection sites have been identified which show the desired variation for particular stresses. Doubled haploid and other segregating populations, including landrace derivatives have been used to map genetically the loci involved. These data can be used in molecular breeding approaches to improve the drought tolerance of barley. One strategy involves screening for genetic markers and physiological traits for drought tolerance, and the associated problem of drought relief-induced mildew susceptibility in naturally droughted fields of North Africa.

Adaptation, Physiological↗

PubMed1995

The Nir1 locus in barley is tightly linked to the nitrite reductase apoprotein gene Nii.

pBNiR1, a cDNA clone encoding part of the barley nitrite reductase apoprotein, was isolated from a barley (cv. Maris Mink) leaf cDNA library using the 1.85 kb insert of the maize nitrite reductase cDNA clone pCIB808 as a heterologous probe. The cDNA insert of pBNiR1 is 503 bp in length. The nucleotide coding sequence could be aligned with the 3' end of other higher plant nitrite reductase apoprotein cDNA sequences but diverges in the 3' untranslated region. The whole-plant barley mutant STA3999, previously isolated from the cultivar Tweed, accumulates nitrite after nitrate treatment in the light, has very much lowered levels of nitrite reductase activity and lacks detectable nitrite reductase cross-reacting material due to a recessive mutation in a single nuclear gene which we have designated Nir1. STA3999 has the characteristics expected of a nitrite reductase apoprotein gene mutant. Here we have used pB-NiR1 in RFLP analysis to determine whether the mutation carried by STA3999 is linked to the nitrite reductase apoprotein gene locus Nii. An RFLP was identified between the wild-type barley cultivars Tweed (major hybridising band of 11.5 kb) and Golden Promise (major hybridising band of 7.5 kb) when DraI-digested DNA was probed with the insert from the partial barley nitrite reductase cDNA clone, pBNiR1. DraI-digested DNA from the mutant STA3999 also exhibited a major hybridising band of 11.5 kb after hybridisation with the insert from pBNiR1.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

PubMed1993

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.

Base Sequence↗

PubMed1992

Association between rDNA alleles and quantitative traits in doubled haploid populations of barley.

Doubled haploids (DH) were generated from reciprocal F1 hybrids which were heterozygous for alleles at the Nor-H3 locus on chromosome 5H of barley. The r-DNA alleles did not deviate significantly from the expected 1:1 ratio and the DH progenies were classified into two groups based on the allelic constitution of the Nor-H3 locus. The DHs were grown in a randomized, replicated field experiment and a range of agronomic and quality traits were recorded. The Nor-H3 locus was associated with a significant portion of the genetic variation for: yield, thousand corn weight, water sensitivity and milling energy requirement of the grain. However, the magnitude of the differences between groups was dependent on the direction of the cross. The milling energy requirement of the grain was consistently associated with alleles at the Nor-H3 locus. These results are presented in relation to the dynamics of rDNA evolution and variability. The potential of molecular markers in conjunction with doubled haploids to map quantitative traits in barley is also discussed.

Alleles↗