Despite a significant growth in food production over the past half-century, one of the most important challenges facing society today is how to feed an expected population of some nine billion by the middle of the 20th century. To meet the expected demand for food without significant increases in prices, it has been estimated that we need to produce 70-100 per cent more food, in light of the growing impacts of climate change, concerns over energy security, regional dietary shifts and the Millennium Development target of halving world poverty and hunger by 2015. The goal for the agricultural sector is no longer simply to maximize productivity, but to optimize across a far more complex landscape of production, rural development, environmental, social justice and food consumption outcomes. However, there remain significant challenges to developing national and international policies that support the wide emergence of more sustainable forms of land use and efficient agricultural production. The lack of information flow between scientists, practitioners and policy makers is known to exacerbate the difficulties, despite increased emphasis upon evidence-based policy. In this paper, we seek to improve dialogue and understanding between agricultural research and policy by identifying the 100 most important questions for global agriculture. These have been compiled using a horizon-scanning approach with leading experts and representatives of major agricultural organizations worldwide. The aim is to use sound scientific evidence to inform decision making and guide policy makers in the future direction of agricultural research priorities and policy support. If addressed, we anticipate that these questions will have a significant impact on global agricultural practices worldwide, while improving the synergy between agricultural policy, practice and research. This research forms part of the UK Government's Foresight Global Food and Farming Futures project

SummaryWe report here evidence of the role that the isoform of the eukaryotic translation initiation factor 4G (eIF(iso)4G) plays in naturally occurring resistance in plant/virus interactions. A genetic and physical mapping approach was developed to isolate the Rymv1 locus controlling the high recessive resistance to Rice yellow mottle virus (RYMV) in the rice (Oryza sativa) variety Gigante. The locus was mapped to a 160-kb interval containing a gene from the eIF(iso)4G family. The stable transformation of a resistant line with the cDNA of this gene, derived from a susceptible variety, resulted in the loss of resistance in transgenic plants. The allelic variability of this gene was analysed in three resistant and 17 susceptible varieties from different cultivated rice species or subspecies. Compared with susceptible varieties, resistant varieties present specific alleles, characterized by either amino acid substitutions or short amino-acid deletions in the middle domain of the protein. The structure of this domain was modelled and showed that the substitutions were clustered on a small surface patch. This suggests that this domain may be involved in an interaction with the virus.

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Detailed studies were conducted on three rice cultivars – IG10, an Oryza glaberrima Steudel; Moroberekan, a traditional Oryza sativa L.; and IDSA6, an improved O. sativa L. – in conditions with and without competition from weeds. IG10 suffered less from competition with weeds and suppressed weeds better than the O. sativa cultivars. IG10 accumulated more biomass, produced more tillers, established a higher leaf area index, had higher specific leaf area and, in the earlier stages of growth, partitioned more of its biomass to leaves than the O. sativa cultivars. Without competition from weeds, grain yields did not significantly differ between the cultivars, but IG10 produced higher yields in competition with weeds. The implications of these findings are discussed in relation to the development of rice plants with good weed suppression characteristics.

SUMMARYIron toxicity is a nutrient disorder associated with high concentrations of iron in soil solutions. Deficiencies of other nutrients, such as P, K, Ca, Mg and Zn, have been implicated in its occurrence in rice plants. Field experiments were carried out in 1992 and 1993 in Ivory Coast to evaluate the iron toxicity tolerance of promising rice cultivars available in West Africa, and to provide additional information for selecting breeding materials. Two sites, differing in their potential to cause iron toxicity, were used. Glasshouse and field studies were also conducted to test the role of other nutrients in the occurrence of iron toxicity. The results showed that genetic tolerance to iron toxicity can significantly improve rice production in iron-toxic soils, with some cultivars producing yields in excess of 5 t/ha. The application of N, P, K and Zn in the field decreased the uptake of iron in rice tops, and this can be a significant factor in the iron-toxicity tolerance of the cultivars.

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Genome-wide linkage disequilibrium (LD) was investigated for 198 accessions of Oryza glaberrima using 93 nuclear microsatellite markers. Significantly elevated levels of LD were detected, even among distantly located markers. Free recombination among loci at the population genetic level was shown (1) by a lack of decay in LD among markers on the same chromosome and (2) by a strictly increasing composite likelihood function for the recombination parameter. This suggested that the elevation in LD was due not to physical linkage but to other factors, such as population structure. A Bayesian clustering analysis confirmed this hypothesis, indicating that the sample of O. glaberrima in this study was subdivided into at least five cryptic subpopulations. Two of these subpopulations clustered with control samples of O. sativa, subspecies indica and japonica, indicating that some O. glaberrima accessions represent admixtures. The remaining three O. glaberrima subpopulations were significantly associated with specific combinations of phenotypic traits-possibly reflecting ecological adaptation to different growing environments.

Phosphorus (P) deficiency is one of the major limiting factor for crop production in highly weathered soils in the humid tropics. Field experiments were conducted for two years (1992 and 1993) to determine P response and efficiencies of upland rice cultivars in an Ultisol, low in available P, in the forest zone of Cote d'Ivoire. The rice cultivars tested were selected from a large number of entries tested earlier for acidity tolerance.Grain yields of the cultivars were significantly increased by P application. There was little further response in grain yield at higher rates than 60 kg P ha -1. The rice cultivars differed in agronomic and physiological P efficiencies and the efficiencies were higher at lower rates of R The rooting depths of the cultivars were increased by application of P at the lowest application rate (30 kg P ha-1).The results suggest that P fertilization of soil acidity-tolerant upland rice cultivars can significantly improve the productivity of the Ultisols.