J. S. Swanston

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.

The effects of major genes on quantitatively varying characters in barley. 4. The GPert and denso loci and quality characters

Random inbred lines derived by doubled haploidy and single seed descent were used to demonstrate that the GPert dwarfing gene, as found in cv. Golden Promise, was associated with low thousand corn weight, main-stem, single plant and plot yield and hot water extract, and high milling energy and levels of screenings. Similarly, the denso dwarfing gene was shown to be associated with late heading, low thousand corn weight, main-stem and single plant yield and high levels of β-glucan and screenings. The associations of the GPert locus with main-stem, single plant and plot yield milling energy and screenings, and of the denso locus with main-stem and single plant yield, were shown to be a result of their association with thousand corn weight. The association of the GPert locus with hot water extract was most likley to be due to linkage, and genes controlling the character may be located on barley chromosome 7. The denso gene may also be linked to genes that control heading date, height, screenings and β-glucan but the chromosomal location of the denso gene is unknown. Amongst lines that possess the GPert gene, correlations between characters were such that the probability of producing a line to combine a high level of plot yield and hot water extract with the dwarfing gene was low.

Use of new EST markers to elucidate the genetic differences in grain protein content between European and North American two-rowed malting barleys.

A population comprising 102 doubled haploid lines were produced from a cross between Beka, a barley cultivar widely grown in Spain, and Logan, a north American cultivar with inherently low protein content, a character considered to derive from the cultivar Karl. The intentions were to determine whether low-nitrogen malting barleys could be developed in Spain, and if genetic factors that influenced protein content were similarly expressed in widely diverse environments, i.e. northeastern Spain and eastern Scotland. An extensive map comprising 187 molecular markers was developed. Expressed sequence-tagged-derived markers were used in addition to anonymous simple sequence repeats to determine the potential for identifying candidate genes for quantitative trait loci (QTLs), and 22 such markers were mapped for the first time. There was transgressive segregation for both yield and protein content, and the gene for low protein from Logan was not expressed in the Scottish environment. In 2002, high yield was associated with earlier heading date in Spain, while late heading at the Scottish site was associated with greater lodging and lower thousand-kernel weight. These appeared to be possible pleiotropic effects of a factor detected on chromosome 2H. Using information from a consensus map, it was shown that this locus on 2H was in the region of the photoperiod response gene Eam6. A QTL explaining 18% of the variation in grain protein content was detected on chromosome 5H in a region in which a gene for nitrate reductase was previously observed. No effect on grain protein was associated with chromosome 6H, which has been suggested as the location of the low protein gene from Karl. However, it is likely that Karl contained more than one genetic factor reducing protein, and we postulate that the gene on 6H may have been lost during the breeding of Logan.

A mutant induced in the malting barley cv Triumph with reduced dormancy and ABA response

Abstract Induced mutants in the barley cultivar Triumph have been screened for reduced dormancy. One line, which germinated readily 2 weeks after harvest, was classified as ABA-insensitive, since it could tolerate a ten-fold increase in ABA, compared to its parent, before germination was inhibited. This mutant, designated TL43, was genotypically similar to Triumph and phenotypically similar under Scottish growing conditions, except for a slightly reduced grain size. In Spain, it showed considerable reductions in both grain yield and plant height, suggesting that it was less widely adapted than its parent. Levels of α-amylase activity were increased at both sites. The mutant appeared to be different from those with ABA insensitivity or altered dormancy previously documented in either barley or Arabidopsis.

Genetical investigations into β-glucan content in barley

SummaryRandom inbred lines produced by doubled haploidy (DH) and single seed descent (SSD) have been used to investigate the genetics of β-glucan (gum) content in barley (Hordeum vulgare). Genetical analyses indicated that gum content is controlled by a simple additive genetic system. Significant negative genetic correlations were observed between β-glucan content, thousand grain weight and height in the DH samples. These correlations were much reduced in the SSD samples and would suggest linkage of the genes controlling these characters. The presence of repulsion linkages could be exploited in a barley breeding programme by producing F1 derived DH to generate recombinants with high thousand grain weight and low β-glucan content. Genetical parameters estimated from DH and F3 samples have successfully been used to predict the number of inbred lines transgressing the parental range for β-glucan content and bivariate combinations involving β-glucan.

Mildew-resistant mutants induced in North American two- and six-rowed malting barley cultivars

Abstract Mildew-resistant mutants were induced with sodium azide in three North American malting barley cultivars, two in the six-rowed Ursula (URS1 and URS2), one in the six-rowed Gertrud (GER1), and one in the two-rowed Prudentia (PRU1). Two of the mutants, URS1 and PRU1, showed complete resistance and were shown to have two new alleles at the mlo locus; these were designated, respectively, mlo31 and mlo32. Mutant URS2, showing partial resistance, was inherited as a dominant gene, but was not an allele at the Mla locus. The mean yield of each mutant was higher than that of its parental line, but yield levels varied across environments, although this was independent of the severity of the mildew attack. Other reasons, for example, the severity of the necrotic lesions in the mutants, may account for yield variations. The malting quality of the GER1 mutant proved similar to that of Gertrud, but both URS1 and URS2 showed lower malt extract than Ursula. This lower extract might be due to the smaller grain size of the mutants that could, in turn, result from necrotic lesions in the leaves, as implied by the effects on grain yield.

Effects on barley grain size, texture and modification during malting associated with three genes on chromosome 1

Abstract Previous studies have suggested that the presence of the three genes waxy ( wx ), short-awned ( lk2 ) and naked ( n ) have an additive effect in increasing β-glucan content. In the genetic background considered in this paper, apparent additive effects were observed in decreasing grain size and increasing water uptake during steeping. Effects of approximately similar magnitude on milling energy and thousand corn weight were observed for wx and lk2 , but these were not consistent across seasons. The waxy gene was associated with a much larger deleterious effect on characters concerned with endosperm modification during malting than lk2 . A combination of wx and n did not demonstrate additive effects on milling energy, hot water extract or cell wall modification. It was postulated that removal of the husk reduced milling energy and facilitated water uptake.

Genetical analysis of a barley mutant with reduced height and increased diastatic power

The United Kingdom produces enough barley grain to meet its needs for animal feed and brewing. The Scottish grain whisky trade, however, imports large quantities of high-diastase barley from Canada (Hayter & Allison, 1975). The breeding of highdiastase cultivars which could be grown in Scotland and so replace these imports has been pursued at the Scottish Crop Research Institute (SCRI).