The rust diseases have plagued cereal cultivation from the early days of domestication. Biblical accounts report on the plight of Hebrews resulting from severe rust epidemics, while the ancient Greeks and Romans made offerings to the corn god, Robigus in attempts to defeat these devastating diseases (McIntosh et al. 1995). Man's approaches to fighting plant disease have changed since the time of the Romans, but still the fight continues. While we may have won many battles, the war is not yet over.

Heritable variation is at the heart of the process of evolution. However, variation is restricted in breeding for uniform crop populations using the pedigree line approach. Pedigree lines are successful in agriculture because synthetic inputs are used to raise fertility and control weeds, pests and diseases. An alternative method promoted for exploring the value of variation and evolutionary fitness in crops is to create composite cross populations. Composite cross populations are formed by assembling seed stocks with diverse evolutionary origins, recombination of these stocks by hybridization, the bulking of F1 progeny, and subsequent natural selection for mass sorting of the progeny in successive natural cropping environments. Composite cross populations can provide dynamic gene pools, which in turn provide a means of conserving germplasm resources: they can also allow selection of heterogeneous crop varieties. The value of composite cross populations in achieving these aims is dependent on the outcome of mass trials by artificial and natural selection acting upon the heterogeneous mixture. There is evidence to suggest that composite cross populations may be an efficient way of providing heterogeneous crops and of selecting superior pure lines for low input systems characterized by unpredictable stress conditions.

The UK rural economy is increasingly driven by consumption-based demands rather than by productive land use. Such demands have been an influence on rural land use for many hundreds of years, but a range of factors, including greater wealth and mobility, have reinforced a long-standing trend for the rural economy to be consumption driven. A number of recent economic analyses and more anecdotal sources are used to furnish evidence of the importance of new consumption demands. It is argued that such demands may impact directly on land markets through land purchase for amenity, etc. and indirectly through bringing affluent people into closer proximity to diversified business opportunities. It is argued that these new economic realities are the dominant drivers of economic change and that their recognition might suggest new approaches to the support of strategies to deliver more sustainable rural development.

Sorghum is grown the world over for both human and animal consumption. Recently, the increase in grain production has slowed; simultaneously, its marketability has declined. Grain size is one of the most important determinants of grain yield and market price in India. One important factor responsible for the decline in consumption of sorghum in India is the inferior quality of rainy season produce. Consumers prefer post rainy season sorghums as the grains are bold, round and lustrous in appearance. Any improvement in the quality of rainy season sorghum grain would help it to fetch higher market prices.

In the present study, the genetics of important grain quality characteristics such as grain size, grain shape and lustre were studied using two crosses based on elite sorghum lines 463B and AKMS 14B, and a germplasm line, IS 17600, during 2001 at the National Research Centre for Sorghum, Hyderabad, India. Generation mean analysis and frequency distribution studies revealed that grain size is governed by dominant genes that are polygenic in nature. Predominance of dominance and epistatic interactions in both crosses indicates that selection for higher grain size would be more effective if the dominance and epistatic effects are first reduced by a few generations of selfing. Biparental mating is suggested for developing homozygous bold grain lines. Round grain shape is governed by a single dominant gene and grain lustre by two complementary recessive genes. The study suggested that developing a sorghum hybrid with bold, round grain is feasible provided either of the parents has bold and/or round grain. However, for the hybrid to be lustrous, both parents need to be lustrous and homozygous for the alleles conferring grain lustre at a common locus. With the possibility of development of sorghum hybrids with bold, round and lustrous grain, there is scope for improvement in consumer preference of rainy season sorghum grain.

The objective was to explore, in lines derived from a bread wheat (Triticum aestivum L.) cultivar, the association of grain yield with carbon isotope discrimination (Δ) and ash content (Ash) determined in both flag leaf and kernel. Divergent selection within the cv. Nestos, based on individual plant yield under very low density (11547 plants/ha), produced 20 lines. Progeny evaluation was conducted in two sites of Northern Hellas (Greece) at both low (11547 plants/ha) and high (5000000 plants/ha) density. The results showed significant differences between lines for grain yield, Δ and Ash. However, only the conclusions on grain yield were similar in low and high density, perhaps because the selection criterion under low density was grain yield. This, combined with the lack of any strong relationship of grain yield with either Δ or Ash, failed to confirm the usefulness of these physiological traits as indirect selection criteria, when the within-cultivar variation for grain yield is exploited. The possible association of grain yield with Δ and Ash appeared to be influenced by various factors such as drought, level of grain yield and altitude. Results also showed that less plant-to-plant variability, as expressed by the coefficients of variation (CV) of single-plant yields, was associated with decreased drought response and higher yield stability. The less stressed lines were those that used water more conservatively till anthesis and maintained a high photosynthetic rate during grain filling.

Seed yield and seed quality determine much of the value of rice (Oryza sativa L.) crops to the producers. The effects of genotype and environment on seed yield and quality were investigated using 12 rice genotypes grown during 3 years (2000–2003) at four different sowing dates in India, where detailed environmental data were collected. Yield, seed weight, proportion of seed setting and quality in terms of potential seed longevity, proportion of discoloured seeds, seed leachate conductivity and percentage germination were evaluated. The results were subjected to analysis of variance and the influence of environmental factors was evaluated by correlation analysis. Analysis of variance suggested that proportion of seed setting, seed leachate conductivity, potential seed longevity, percentage seed germination and proportion of seed discoloration were influenced more by environmental effects than by genotypic effects. In contrast, yield, panicle number, seed weight, and proportion of high-density grains were influenced more by genotypic than by environmental effects. The significant interaction effects of genotype and environment for all characteristics were attributed to differential resistance of genotypes to lodging (caused by increased plant height, low radiation and excessive rain at the time of grain filling) and were associated with fewer panicles harvested, lower seed setting and lower seed weight. Correlation analysis suggested that warm weather conditions with high solar radiation and without excessive rains during grain filling stage gave the best rice seed yield with high quality.

Simple models that can forecast yield loss from weed seedling density at crop emergence are useful tools for both research and practice. In 1985 Cousens presented the rectangular hyperbolic curve as a solution to this problem for the one-weed species case (Cousens 1985a). To address the multi-weed species case, the present theoretical paper investigates two published models and develops a third model, termed ‘recursive density equivalents’. The models were analysed and evaluated based on their biological rationale and using already published data. The earlier models were both found to rely on biologically unrealistic assumptions. The new model avoided additional assumptions, providing a neutral method of summarizing the Cousens curves for many species. Recursive density equivalents were found to be additive in a more intuitive fashion than the ‘density equivalents’ introduced earlier. An over-estimation bias was found to be inherent in the earlier density equivalents model, increasing with species richness. The new model corrected for this bias when checked against one year's field data but for another year, both models over-estimated markedly. All three models were found to be too simple to accommodate all possible modes of intra- and inter-specific competition, yet the new model is an improvement, as it agrees better with the biological principles of crop-weed competition.

Flax fibre for industrial purposes differs from that for linen production, although the agronomic factors that influence fibre development and which factors are most important for industrial fibre production have still to be defined. A description of variations in the performance of fibre flax varieties is also necessary as current guidance relates to the European market rather than the UK. Field trials were sown in 2002 and 2003 at the Henfaes Research Centre in north Wales, investigating 29 and 26 varieties, respectively, of European fibre flax and dual-purpose flax varieties. In 2002 a nitrogen treatment was included in the trial with two treatments, 40 kg/ha and 80 kg/ha. Varieties were evaluated for 20 agronomic and fibre production variables, and the differences between the varieties were analysed using analysis of variance (ANOVA) and principal components analysis (PCA). The higher nitrogen rate was found to increase crop lodging, although some varieties were found to be more susceptible than others. Environment had a strong influence on crop success, with some varieties showing more year to year stability than others. PCA allowed those varieties that were the highest yielding, highest fibre producers and showed the best stability across the 2 years to be identified. Understanding the agronomic results presented and discussed here is important if fibre flax production is to become economically viable in the UK.

The objective of the study was to determine the in vivo relationship between the long-term administration of recombinant bovine somatotropin (rbST), circulating levels of IGF-I and insulin, mammary blood flow and other variables relevant to milk synthesis, in crossbred, Holstein cattle. Ten first-lactation, non-pregnant, crossbred, Holstein dairy cattle were divided into two groups of five animals each; an experimental group and a control group. Animals in each group were fed with rice straw, treated with 5 kg urea dissolved in 100 litres water per 100 kg dry rice straw as the source of roughage. Four consecutive study periods were carried out in each group. These consisted of a pretreatment period (45 days postpartum before lactation peak) and three treatment periods during early lactation (105 days postpartum), mid-lactation (165 days postpartum) and late lactation (225 days postpartum). During the treatment periods, animals that had completed 60 days of lactation were injected subcutaneously at fortnightly intervals with 500 mg of recombinant bovine somatotropin (rbST) (POSILAC, Monsanto, USA) in the experimental group, while animals in the control group were injected subcutaneously at fortnightly intervals with 800 mg of sterile sesame oil, without rbST, as a placebo. During the pretreatment period, there were no significant differences in plasma concentrations of IGF-I, insulin and other parameters between the control group and the experimental group. During the treatment periods, the increase in the concentration of plasma IGF-I in rbST treated animals was significantly higher than in the control animals throughout the lactation period. Plasma glucose, protein and triglyceride concentrations in each group remained stable throughout the study. The total daily dry matter intakes were not significantly different between the groups. Milk yield increased by 20% with rbST treatment and it was 22% greater than that of the control animals receiving placebo in early lactation. Milk yield of rbST treated animals rose to a peak in early lactation and then gradually declined. In late lactation, milk yield of rbST-treated animals decreased by 19% as compared with early lactation. Udder plasma flow and udder blood flow markedly increased with rbST treatment and there were no significant changes in the control animals. The ratio of udder blood flow to the rate of milk production increased in mid- and late lactation in controls and the rbST treated animals. These findings suggest that the short persistency of lactation in rbST treated animals was similar to that in the control animals receiving placebo. Changes in milk production during the progress of lactation in rbST treated animals might not be controlled systemically only but also locally within the mammary gland. The lack of effect of higher plasma IGF-I levels on persistency of lactation in rbST treated animals, may be due to changes in the pattern of IGF-I binding proteins and paracrine production inhibiting IGF-I action.

This group, which is concerned with the applications of mathematics to agricultural science, was formed in 1970 and has since met at approximately yearly intervals in London for one-day meetings. The thirty-seventh meeting of the group, chaired by J. Craigon of The University of Nottingham, was held in the Kohn Centre at the Royal Society, 6 Carlton House Terrace, London on Friday, 8 April 2005 when the following papers were read.