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R A Richards

Publications and source records attributed to R A Richards.

6 recordsLinked to original sources
PubMed2005

Molecular mapping of gibberellin-responsive dwarfing genes in bread wheat.

Opportunities exist for replacing reduced height (Rht) genes Rht-B1b and Rht-D1b with alternative dwarfing genes for bread wheat improvement. In this study, the chromosomal locations of several height-reducing genes were determined by screening populations of recombinant inbred lines or doubled haploid lines varying for plant height with microsatellite markers. Linked markers were found for Rht5 (on chromosome 3BS), Rht12 (5AL) and Rht13 (7BS), which accounted for most of the phenotypic variance in height in the respective populations. Large height differences between genotypes (up to 43 cm) indicated linkage to major height-reducing genes. Rht4 was associated with molecular markers on chromosome 2BL, accounting for up to 30% of the variance in height. Confirming previous studies, Rht8 was linked to markers on chromosome 2DS, whereas a population varying for Rht9 revealed a region with a small but significant height effect on chromosome 5AL. The height-reducing effect of these dwarfing genes was repeatable across a range of environments. The molecular markers developed in this study will be useful for marker-assisted selection of alternative height-reducing genes, and to better understand the effects of different Rht genes on wheat growth and agronomic performance.

Bread↗
PubMed2004

Breeding for high water-use efficiency.

There is a pressing need to improve the water-use efficiency of rain-fed and irrigated crop production. Breeding crop varieties with higher water-use efficiency is seen as providing part of the solution. Three key processes can be exploited in breeding for high water-use efficiency: (i) moving more of the available water through the crop rather than it being wasted as evaporation from the soil surface or drainage beyond the root zone or being left behind in the root zone at harvest; (ii) acquiring more carbon (biomass) in exchange for the water transpired by the crop, i.e. improving crop transpiration efficiency; (iii) partitioning more of the achieved biomass into the harvested product. The relative importance of any one of these processes will vary depending on how water availability varies during the crop cycle. However, these three processes are not independent. Targeting specific traits to improve one process may have detrimental effects on the other two, but there may also be positive interactions. Progress in breeding for improved water-use efficiency of rain-fed wheat is reviewed to illustrate the nature of some of these interactions and to highlight opportunities that may be exploited in other crops as well as potential pitfalls. For C3 species, measuring carbon isotope discrimination provides a powerful means of improving water-use efficiency of leaf gas exchange, but experience has shown that improvements in leaf-level water-use efficiency may not always translate into higher crop water-use efficiency or yield. In fact, the reverse has frequently been observed. Reasons for this are explored in some detail. Crop simulation modelling can be used to assess the likely impact on water-use efficiency and yield of changing the expression of traits of interest. Results of such simulations indicate that greater progress may be achieved by pyramiding traits so that potential negative effects of individual traits are neutralized. DNA-based selection techniques may assist in such a strategy.

Agriculture↗
PubMed2004

Comparative mapping of wheat chromosome 1AS which contains the tiller inhibition gene (tin) with rice chromosome 5S.

The capacity to tiller is a key factor that determines plant architecture. Using molecular markers, a single major gene reducing tiller number, formally named the tiller inhibition gene ( tin), was mapped to the short arm of chromosome 1A in wheat. We identified a tightly linked microsatellite marker ( Xgwm136) that may be useful in future marker-assisted selection. The tin gene was mapped to the distal deletion bin of chromosome 1AS (FLM value 0.86) and wheat ESTs which were previously mapped to the same deletion bin were used to identify 18 closely related sequences in the syntenic region of rice chromosome 5. For a subset of wheat ESTs that detected flanking markers for tin, we identified closely related sequences within the most distal 300 kb of rice chromosome 5S. The synteny between the distal chromosome ends of wheat 1AS and rice 5S appeared to be disrupted at the hairy glume locus and seed storage protein loci. We compared map position of tin with other reduced tillering mutants characterised in other cereals to identify possible orthologous genes.

Chromosome Mapping↗
PubMed2000

Selectable traits to increase crop photosynthesis and yield of grain crops.

The grain yield of cereals has almost doubled this century as a result of genetic manipulation by plant breeding. Surprisingly, there has been no change in the rate of photosynthesis per unit leaf area to accompany these increases. However, total photosynthesis has increased as a result of an increase in leaf area, daily duration of photosynthesis or leaf area duration. There remain substantial opportunities to continue to improve total photosynthesis and crop yield genetically using conventional breeding practices. Selectable traits are discussed here in the context of increasing total above-ground biomass under favourable conditions. Opportunities exist to alter crop duration and the timing of crop development to match it better to radiation, temperature and vapour pressure during crop growth, and to increase the rate of development of early leaf area to achieve rapid canopy closure. The importance of these traits will depend on the environment in which the crop is grown. Increases in crop photosynthesis through breeding are also likely to come via indirect means. Selection for a high and sustained stomatal conductance during the period of stem elongation is one way. Increasing assimilate allocation to the reproductive primordia so as to establish a large potential sink should also indirectly increase total crop photosynthesis. Evidence in the major grain crops suggests that by anthesis the capacity for photosynthesis is high and that photosynthesis is not limiting during grain filling. To use this surplus capacity it is suggested that carbon and nitrogen partitioning to the reproductive meristem be increased so as to establish a high potential grain number and the potential for a large grain size. It is then expected that additional photosynthesis will follow, either by a longer daily duration of photosynthesis or by an extended leaf area duration.

Biomass↗