Increases in atmospheric CO₂ had impacts on plant evolution throughout geological times and enabled mass selection of productive crop ancestors. Recent studies suggest that the ongoing CO₂ fertilisation justifies the establishment of breeding programs to develop crops whose yield will profit from the greater availability of carbon without compromising seed quality. It has been shown that old cultivars may respond more strongly to CO₂ enrichment than their modern counterparts. In order to address this issue, old and modern cereal cultivars (wheat, spelt, barley and rye) and ancestors of wheat (Aegilops, einkorn, emmer) were grown at ambient (380 ppm) and expected future (550 ppm) concentrations of CO₂ in growth chambers simulating a seasonal climate typical for south-west Germany. Phenology, senescence, growth, yield formation and seed quality (ash and nitrogen (N) concentrations) were assessed and the CO₂ response ratio (RR, i.e. performance under elevated v. ambient CO₂) of the parameters was evaluated with respect to the year of cultivar release. Across the 32 accessions tested, seed mass increased by 34% under elevated CO₂, whereas seed ash and N concentrations decreased by 8 and 10%, respectively, with large inter- and intra-specific variation. Yields of modern wheat and barley cultivars proved higher than of old cultivars, but only in barley was RR higher in the older cultivars. Some accessions showed deviations from the negative relationship between seed mass and N concentration, rendering them suitable candidates for developing cultivars adapted to high CO₂.

Durum wheat is one of the most important staple food crops, grown mainly in the Mediterranean region where its productivity is drastically affected by salinity. The objective of this study was to identify markers associated with grain yield and its related traits under saline conditions. A population of 114 F₈ recombinant inbred lines (RILs) was derived by single-seed descent from a cross between Belikh2 (salinity-tolerant variety) and Omrabi5 (less salinity tolerant) was grown under non-saline and saline conditions in a glasshouse. Phenotypic data of the RILs and parental lines were measured for 15 agronomic traits. Association of 96 simple sequence repeat (SSR) loci covering all 14 chromosomes with 15 agronomic traits was analysed with a mixed linear model. In total, 49 SSR loci were significantly associated with these traits. Under saline conditions, 12 markers were associated with phenological traits and 19 markers were associated with yield and yield components. Marker alleles from Belikh2 were associated with a positive effect for the majority of markers associated with yield and yield components. Under saline condition, five markers (Xwmc182, Xwmc388, Xwmc398, Xbarc61, and Xwmc177) were closely linked with grain yield, located on chromosomes 2A, 3A, 3B, 4B, 5A, 6B, and 7A. These markers could be used for marker-assisted selection in durum wheat breeding under saline conditions.

Localised supply of phosphorus (P) plus ammonium improves root proliferation and nutrient uptake by plants grown on calcareous soils, but how nitrogen (N) forms (ammonium and urea) and placements affect maize (Zea mays L.) root distribution and nutrient uptake is not fully understood. A soil column study was conducted with four N and P combinations including P plus urea (UP), mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP) and P plus ammonium sulfate (ASP), and two fertiliser application methods (banding in the 10–25 cm layer or mixing throughout the 45-cm soil profile). Shoot N and P content increased by 11–31% and 14–37% in the treatments with banding P plus ammonium (MAP, DAP or ASP) compared with banding UP and the mixing treatments. Shoot N and P uptake rates per root dry weight or root length were higher with banding P plus ammonium than their respective mixing treatments. Banding P plus ammonium increased root-length density in the fertiliser-banded layer compared with banding UP and the mixing treatments. The results show that modifying root spatial distribution by banding P plus ammonium leads to an increase in N and P uptake rates, and consequently enhances nutrient accumulation by maize.

The processes involving pH modification, carboxylate exudation and phosphorus (P) dynamics in the rhizosphere of crops grown in intercropping are poorly understood. Two groups of maize (Zea mays L.) or faba bean (Vicia faba L.) plants (monocropping) or one group of plant of each species (intercropping) were grown between three 1-mm-thick soil layers; the central soil layer is referred to as inter-rhizosphere, and the two outer soil layers are designated sole-rhizosphere. Faba bean intercropped with maize had an 11% increase in shoot biomass and a 15% increase in P uptake compared with monocropped faba bean. The cropping pattern did not significantly influence maize growth. After 4 weeks of growth, faba bean significantly decreased soil pH in both the sole- and inter-rhizosphere in monocropping, but no effects were apparent for the intercropping rhizosphere. The major carboxylates in the rhizosphere of faba bean were malate (18–45 nmol g^–1 soil) and maleate (1.2–2.4 nmol g^–1 soil). Only trace amounts of carboxylates were measured in the rhizosphere of monocropped maize. However, intercropped maize had a high concentration of malate (∼11 nmol g^–1 soil) in both sole- and inter-rhizosphere; the malate was likely exuded by faba bean and was then diffused to the sole-rhizosphere of intercropped maize. The amount of malate exuded by intercropped faba bean was 19% higher than with monocropped plants. The results indicate that diffusion of protons and carboxylates extended the interaction zone between maize and faba bean, and may have contributed to enhancements of P uptake in the intercropping system.

Tropical pasture systems are typically dominated by C₄ grasses growing on nitrogen (N) deficient soils. Under these conditions, N₂-fixing legumes should have a competitive advantage, yet low legume contents are often reported in these systems. This work investigates whether below-ground competition for phosphorus (P) is limiting the ability of legumes to compete in swards of C₄ grasses when grown in a sand matrix. The external P requirement of a subtropical legume (butterfly pea, Clitoria ternatea L.) and a C₄ grass (buffel grass, Cenchrus ciliaris L.) were initially determined in a P-response experiment. Four rates of P (4.6–78.2 mg P kg^–1 of Colwell P) were subsequently selected to investigate the growth response of the butterfly pea when grown with and without competition from a sward of N-deficient buffel grass. Shoot dry matter was determined over successive cuts and P uptake determined at the final harvest at 72 days. Buffel grass dominated the mixed swards and reduced the shoot dry matter production of the butterfly pea by >50% relative to the pure swards. A significant difference in the soil P response curve and shoot P uptake of butterfly pea was not detected between pure swards and those with competition from buffel grass. The ability of C₄ grasses to acquire and convert resources (i.e. light, water and nutrients) more efficiently into shoot dry matter is likely to be a major factor resulting in grass-dominated pastures in tropical systems.

Three major simple sequence repeat (SSR) groups were identified in a global collection of 164 oilseed Brassica rapa based on allelic diversity at loci: SSR group 1 (south Asia, predominantly from India, Pakistan, and Nepal); SSR group 2 (predominantly southern and eastern Europe with mostly winter and semi-winter types); and SSR group 3 (northern Europe, mostly from Germany, and many of unknown origin). Nine outliers from several regions were placed in a fourth SSR group, which had the highest allelic diversity per accession of all SSR groups. Analysis of molecular variance of SSR data supported four groups but indicated that genetic variance within populations was high (84%) compared with variance between populations. Flowering habit was classified as winter, spring or semi-winter type, and pollination control as self-incompatible or self-compatible. These phenotypes were distributed across each of the three SSR groups and outliers, although most SSR group 1 accessions were self-compatible spring types, and winter types were mainly from SSR groups 2 and 3. Two SSR sub-groups were present among Indian accessions, both of which contained brown-seeded types, but only one sub-group contained yellow-seeded types (most likely yellow sarson). Eleven B. rapa accessions were misclassified in genebanks as oilseed types but were re-classified as leafy or root vegetable types, and 12 accessions were misclassified as B. rapa and were shown to be allotetraploid or other Brassica species.

Napier grass (Pennisetum purpureum Schumach.) is an important fodder and relatively drought-tolerant crop in tropical and subtropical regions, especially in developing countries. For this and other species, tools are needed for identifying drought-tolerant cultivars to aid selection for semi-arid environments. We determined tissue water status, carbon assimilation, biomass yield and forage quality for Napier grass cvv. Bana and Atherton grown in bins and subjected to three soil-water supply levels (100, 50 or 25% of field capacity) in glasshouses set at either low (15−25°C) or high (25−35°C) temperature regimes, over three growing cycles. Our aim was to explore whether differences in leaf water potential (LWP) and carbon assimilation rates could be reliable indicators of the relative yield potential and forage quality of the two cultivars in environments prone to water and heat stresses.

At the low soil-water supply of 25% and low temperature, Bana had lower (more negative) LWP and relative water content (RWC) than Atherton, while at 50% and 100% soil-water supply, Bana had a higher tissue water status. Under the high temperature regime, Bana had consistently more positive LWP and RWC than Atherton, but the differences were not significant. The two cultivars had a similar CO₂ assimilation rate (A) and there were no significant differences in the total dry matter yields over the three growing cycles. Water-use efficiency for above-ground biomass (kg ha^–1 mm^–1) was similar for both cultivars and was 28.5–35.1 under the low temperature regime and 16.9–22.9 under the high temperature regime. Neutral detergent fibre (NDF) was often higher for Bana at low water supply and low temperature than for Atherton, but the trend was reversed under the high temperature regime. Digestibility was generally improved under water-stressed conditions, and there was a positive correlation between NDF and both LWP and RWC measured at midday, but only under the low temperature regime. We conclude that LWP, RWC and A, alone or together, are inadequate for selecting cultivars for dry and hot environments, because cultivars may differ in other mechanistic responses to water stress and high temperatures.

Ecological studies often suggest that natural grasslands with high species diversity will grow more biomass and leach less nitrogen (N). If this diversity effect also applies to fertilised and irrigated pastures with controlled removal of herbage, it might be exploited to design pastures that can assist the dairy industry to maintain production while reducing N leaching losses. The purpose of this study was to test whether pasture mixtures with a high functional diversity in ryegrass traits will confer on the system higher water- and N-use efficiency. The hypothesis was tested using a process-based model in which pasture mixtures were created with varying levels of diversity in ryegrass traits likely to affect pasture growth. Those traits were: the winter- or summer-dominance of growth, the ability of the plant to intercept radiation at low pasture mass, and rooting depth. Pasture production, leaching and water- and N-use efficiency were simulated for management typical of a dairy pasture. We found that the performance of the diverse ryegrass–clover mixtures was more strongly associated with the performance of the individual components than with the diversity across the components. Diverse pasture mixtures may confer other benefits, e.g. pest or disease resistance and pasture persistence. The testing here was within a selection of ryegrasses, and the greater possible diversity across species may produce different effects. However, these results suggest that highly performing pastures under fertilised and irrigated grazed conditions are best constructed by selecting components that perform well individually than by deliberately introducing diversity between components.