Lesley Fish

A Genetic Framework for Grain Size and Shape Variation in Wheat

Using large-scale quantitative analysis, this work reveals that grain shape and size are independent traits in both modern and primitive wheat and are under the control of distinct genetic components. Moreover, the phenotypic diversity in grain morphology found in modern commercial wheat is the result of a recent and severe bottleneck. Grain morphology in wheat (Triticum aestivum) has been selected and manipulated even in very early agrarian societies and remains a major breeding target. We undertook a large-scale quantitative analysis to determine the genetic basis of the phenotypic diversity in wheat grain morphology. A high-throughput method was used to capture grain size and shape variation in multiple mapping populations, elite varieties, and a broad collection of ancestral wheat species. This analysis reveals that grain size and shape are largely independent traits in both primitive wheat and in modern varieties. This phenotypic structure was retained across the mapping populations studied, suggesting that these traits are under the control of a limited number of discrete genetic components. We identified the underlying genes as quantitative trait loci that are distinct for grain size and shape and are largely shared between the different mapping populations. Moreover, our results show a significant reduction of phenotypic variation in grain shape in the modern germplasm pool compared with the ancestral wheat species, probably as a result of a relatively recent bottleneck. Therefore, this study provides the genetic underpinnings of an emerging phenotypic model where wheat domestication has transformed a long thin primitive grain to a wider and shorter modern grain.

Mapping genes for flowering time and frost tolerance in cereals using precise genetic stocks

The development of comprehensive genetic maps based on molecular markers has increased the power of genetical analysis immensely in the last few years. Characters previously recalcitrant to analysis, such as abiotic stress responses, are now amenable, and individual major genes and QTL mediating the variation can be identified. This has allowed the development of strategies for stress amelioration by adjusting the timing of the life cycle and introducing genes which enable the plant to tolerate stress. These strategies are illustrated here by showing how genes for vernalization response and cold tolerance on chromosomes 5A and 5D of wheat have been identified and located. Additionally, their relationships to genes in other species, such as barley and rice can be characterised through comparative mapping approaches, leading to strategies for their isolation using rice genomic tools.

Development of consistently crossable wheat genotypes for alien wheat gene transfer through fine-mapping of the Kr1 locus

Breeders can force sexual hybridisation between wheat and related grass species to produce interspecific hybrids containing a dihaploid set of wheat and related chromosomes. This facilitates the introgression of desirable genes into wheat from the secondary gene pool. However, most elite European wheat varieties carry genes that suppress crossability, making the transfer of novel traits from exotic germplasm into elite wheat varieties difficult or impossible. Previous studies have identified at least five crossability loci in wheat. Here, the crossability locus with the largest effect, Kr1 on chromosome arm 5BL, was fine-mapped by developing a series of recombinant substitution lines in which the genome of the normally non-crossable wheat variety ‘Hobbit sib’ carries a recombinant 5BL chromosome arm containing segments from the crossable variety ‘Chinese Spring’. These recombinant lines were scored for their ability to cross with rye over four seasons. Analysis revealed at least two regions on 5BL affecting crossability, including the Kr1 locus. However, the ability to set seed is highly dependent on prevailing environmental conditions. Typically, even crossable wheat lines exhibit little or no seed set when crossed with rye in winter, but show up to 90% seed set from similar crosses made in summer. By recombining different combinations of the two regions affecting crossability, wheat lines that consistently exhibit up to 50% seed set, whether crossed in the UK winter or summer conditions, were generated, thus creating a very important tool for increasing the efficiency of alien wheat transfer programmes.

Physiological traits influencing hardness and vitreosity in wheat grain

ABSTRACT Of the 2 million ha of wheat grown annually in the UK, about 700,000 ha are grown on drought-prone soils. With predicted climate change, the frequency of summer droughts is likely to increase. By mapping genes controlling improved end-use quality under stress, the objective is to provide UK plant breeders with information on genes, and selection methods for traits conferring more stable end-use quality under drought-stress conditions. A mapping population of 48 doubled haploid lines and their parents (Beaver & Soissons), has been investigated over two seasons (2002 and 2003 harvest years), on a drought-prone, loamy sand at ADAS Gleadthorpe. The different lines were grown both with, and without irrigation, in fully replicated field experiments, to examine the differential response of the lines to drought. Physiological assessments were made throughout the season, and yield determined at grain maturity. Hand harvested grain was assessed for mealiness (=100-vitreosity), hardness, grain size, grain weight, grain protein content and measurements made of gel protein quality. The initial observations suggest that the effect of drought was to reduce grain size, increase grain crude protein concentration, and to increase vitreosity of the grain. At the same time, grain protein quality was improved, and grain hardness increased under drought conditions. New QTL have been identified and further work is ongoing to understand the interactions between genotype and environment on grain quality in these lines.