Further genetic gains in wheat yield are required to match expected increases in demand. This may require the identification of physiological attributes able to produce such improvement, as well as the genetic bases controlling those traits in order to facilitate their manipulation. In the present paper, a theoretical framework of source and sink limitation to wheat yield is presented and the fine-tuning of crop development as an alternative for increasing yield potential is discussed. Following a top-down approach, most crop physiologists have agreed that the main attribute explaining past genetic gains in yield was harvest index (HI). By virtue of previous success, no further gains may be expected in HI and an alternative must be found. Using a bottom-up approach, the present paper firstly provides evidence on the generalized sink-limited condition of grain growth, determining that for further increases in yield potential, sink strength during grain filling has to be increased. The focus should be on further increasing grain number per m2, through fine-tuning pre-anthesis developmental patterns. The phase of rapid spike growth period (RSGP) is critical for grain number determination and increasing spike growth during pre-anthesis would result in an increased number of grains. This might be achieved by lengthening the duration of the phase (though without altering flowering time), as there is genotypic variation in the proportion of pre-anthesis time elapsed either before or after the onset of the stem elongation phase. Photoperiod sensitivity during RSGP could be then used as a genetic tool to further increase grain number, since slower development results in smoother floret development and more floret primordia achieve the fertile floret stage, able to produce a grain. Far less progress has been achieved on the genetic control of this attribute. None of the well-known major Ppd alleles seems to be consistently responsible for RSGP sensitivity. Alternatives for identifying the genetic factors responsible for this sensitivity (e.g. quantitative trait locus (QTL) identification in mapping populations) are being considered.

The objective of the present study was to determine the optimum plant density of four pigeonpea genotypes, representing early, medium and late maturing types, grown in five contrasting environments in Tanzania. ICPL 86005 (early), Kat 50/3 and QP 37 (medium) and Local (late) were grown at four plant densities (40 000–320 000 plants/ha) in irrigated and rainfed conditions at Ilonga and under rainfed conditions at Kibaha, Selian and Ismani. At maturity, total above-ground biomass and seed yield (SY) were measured. The highest yields were obtained in the irrigated experiment at Ilonga, where the medium/late genotypes produced 25 t biomass/ha and 5·6 t seed/ha. The lowest SY were at Kibaha, 0·58 to 1·76 t/ha, where a severe drought occurred. In nearly all cases the response to density was linear or asymptotic. The response of ICPL 86005 was significantly different from the other three genotypes. The optimum density for SY varied from 37 000 to 227 000 plants/ha in ICPL 86005, compared with 3000 to 101 000 plants/ha in the medium/late genotypes. The highest optimum density was at Selian and Ismani and the lowest at Ilonga and Kibaha, where drought occurred. Optimum densities therefore varied greatly with genotype (duration) and environment, and this variation needs to be considered when planning trials.

Crop yield and optimum nitrogen fertilization rates (Nopt) are often calculated ex post by specific functions of the nitrogen fertilization rate, but in doing this, uncertainties in terms of model choice, annual nitrogen response variations and parameter estimation are neglected. In the present study, Nopt, grain yields, net revenues and N balances were estimated for the three crops of an oilseed rape (OSR)–winter wheat–winter barley rotation. The effects of uncertainties were considered using three different statistical models, estimating an identical Nopt over the years and carrying out Monte-Carlo simulations where model parameters were varied according to their estimated standard errors. The statistical models used were the quadratic (Q) polynomial function, the linear response and plateau (LRP) function and the quadratic response and plateau (QRP) function.

The Q model tended to estimate the highest Nopt values for the three crops, followed by the QRP and the LRP model in an initial ex post analysis. The highest corresponding mean net revenues in the rotation were estimated by the LRP model, followed by the Q and QRP model; mean N balances increased in the order LRP, QRP and Q. In the comparison of the crops, OSR showed the highest N balances followed by wheat and barley. Considering the protein concentration in wheat, Nopt values estimated by the Q model were considerably higher than without the economic effects of grain quality.

In order to consider uncertainties in annual nitrogen response, an ex ante Nopt over the years was determined by maximizing the cumulated net revenues over all years in the rotation. Ex ante Nopt was higher as the mean of the ex post Nopt values for the QRP and LRP model. Average grain yields and net revenues were lower, N balances were higher. Running the Monte-Carlo simulations, ex post Nopt was obtained by 10 000 generated functions in each year and ex ante Nopt by 50 000 generated functions of years 1996, 1997, 1998, 1999 and 2002. This led to an increase in Nopt especially for the LRP model, while effects on the estimation of Nopt by the Q model were rather small. For the LRP model, corresponding mean net revenue decreased and mean N balance rose. In contrast, due to marginal changes in Nopt, the consideration of uncertainties in the estimations had only a small effect on net revenue and N balance in the Q model.

In general, all kinds of uncertainty tended to increase Nopt but this effect was much higher for the LRP model as compared to the Q model. This increase in Nopt was associated with decreasing net revenues and increasing N balances. Exceptionally in OSR using the Q model, however, the ex ante approaches considering uncertainty led to slightly lower Nopt values compared to the ex post value.

The low activity and the competing reactions catalysed by Rubisco are major limitations to photosynthetic carbon assimilation in C3 plants; the present paper considers how these limitations can be overcome. The limitations could be most effectively addressed by introducing Rubisco with a higher catalytic rate and/or better able to discriminate between gaseous substrates. Although enzymes with desirable characteristics are available, technical advances are required before their potential can be realized in major crop plants. Significant improvements could be achieved also by increasing the concentrations of the productive substrates, CO2 and RuBP, at the active site of Rubisco. Critically, it is essential that other environmental and genotype constraints are minimized, to realize the highest photosynthetic potential.

In plant physiology and breeding, it is important to understand the causes of genotype×environment interactions (GEIs) of complex traits such as grain yield. It is difficult to study the underlying sequential biological processes of such traits, their components and other intermediate traits, as well as the main environmental factors affecting those processes. The structural equation models (SEMs) used in the present study allow the external and internal factors affecting GEI of various traits and their interrelations to be accounted for. The study included 86 wheat genotypes derived from three different crosses and evaluated over 3 years. Several attributes, as well as grain yield and yield components, were measured during five crop development stages. Environmental data for the five development stages were averaged. The SEM approach facilitated comprehensive understanding of GEI effects among the different traits, and decomposed the total effects of grain yield components and cross-product covariates on grain yield GEI into direct and indirect effects. External climatic variables were related mostly to main final yield components, and only more intermediate endogenous variables, such as spikes/m2, were affected by minimum temperature and radiation in the early stages of plant development.

The objective of the present research was to study the genetic variability for total dry matter (DM) yield, tiller number, heading date and three quality traits, namely content of digestible dry matter (DDM), water-soluble carbohydrate (WSC) and crude protein (CP), in cocksfoot (Dactylis glomerata L.). Twenty-five parents were randomly chosen from a genetically broad-based population, and their respective half-sib (HS) families were generated. Clonally-propagated parents and their HS family seeds were grown as individual plants using a randomized complete block design with two replications in Alborz Research Center, Karaj, Iran, during 2002–04. The results of combined analyses over 2 years showed significant variances between clonal parents for all traits except CP. In the HS generation, between-family variances were only significant for tiller number, heading date and WSC. Clone×year (S2GY) and family×year (S2FY) interactions were significant for all traits except for WSC in HS families. The estimates of broad-sense heritability (h2b) were moderate to high for all traits (h2b=0·37–0·69), except CP. Narrow-sense heritability (h2n) estimates from analyses of progenies and from regression of HS progenies on parents (h2op) were moderate, relatively the same values as h2b for heading date, tiller number and WSC, which suggested that additive genetic variance was the main component controlling these traits. For DM yield and DDM, h2n and h2op estimates were low, whereas h2b estimates were moderate, which suggested that both additive and non-additive gene effects played an important role in the genetic regulation of these traits. Genetic correlations among CP with both WSC and DDM were generally negative, whereas WSC was positively correlated with DDM and tiller number. The genetic correlation among DM yield with DDM was weak and inconsistent and, in general, negative. DM yield had negative and positive correlation with heading date and tiller number, respectively. It was concluded that there was significant variation and moderate heritability for most traits in the cocksfoot populations evaluated to improve yield and quality traits. Selection for high WSC is a means to improve quality in general. The data also indicate that response to combined selection for both DDM and DM yield should be possible. Selection for DDM alone could result in reduction in yield.

The effects of intercropping wheat with faba bean (Denmark, Germany, Italy and UK) and wheat with pea (France), in additive and replacement designs on grain nitrogen and sulphur concentrations were studied in field experiments in the 2002/03, 2003/04 and 2004/05 growing seasons. Intercropping wheat with grain legumes regularly increased the nitrogen concentration of the cereal grain, irrespective of design or location. Sulphur concentration of the cereal was also increased by intercropping, but less regularly and to a lesser extent compared with effects on nitrogen concentration. Nitrogen concentration (g/kg) in wheat additively intercropped with faba bean was increased by 8% across all sites (weighted for inverse of variance), but sulphur concentration was only increased by 4%, so N:S ratio was also increased by 4%. Intercropping wheat with grain legumes increased sodium dodecyl sulphate (SDS)-sedimentation volume. The effect of intercropping on wheat nitrogen concentration was greatest when intercropping had the most deleterious effect on wheat yield and the least deleterious effect on pulse yield. Over all sites and seasons, and irrespective of whether the design was additive or replacement, increases in crude protein concentration in the wheat of 10 g/kg by intercropping with faba bean were associated with 25–30% yield reduction of the wheat, compared with sole-cropped wheat. It was concluded that the increase in protein concentration of wheat grain in intercrops could be of economic benefit when selling wheat for breadmaking, but only if the bean crop was also marketed effectively.

Wheat is grown on 210 million ha throughout the world producing approximately 600 million tonnes of grain (10 year average; FAO 2005) and providing on average one fifth of the total calorific input of the world's population (FAO 2003). For some regions such as North Africa, Turkey and Central Asia, wheat provides half of total dietary energy intake. Of the cultivated wheat area, half is located in less developed countries where there have been steady increases in productivity since the green revolution, associated with genetic improvements in yield potential, resistance to diseases and adaptation to abiotic stresses (Reynolds & Borlaug 2006a, b) as well as better agronomic practices (Derpsch 2005). Nonetheless, challenges to wheat production are still considerable, especially in the developing world, not only because of increased demand but also because of the increased scarcity of water resources (Rosegrant 1997; WMO 1997), ever more unpredictable climates (Fischer et al. 2002), increased urbanization and loss of good quality land away from agriculture (Hobbs 2007), and decreased public sector investment in agriculture and rural affairs (Falcon & Naylor 2005). To meet demand in a sustainable way, more resources are required to breed a new generation of genetically improved cultivars as well as implement resource-conserving agronomic management practices.

Ethiopian mustard (Brassica carinata) genotypes with different contents of oleic acid (C18:1) in the seed oil could be useful for food and industrial applications. The objectives of the present research were to study the inheritance of high C18:1 in the seed oil of different lines of Ethiopian mustard and its relationship with erucic acid content (C22:1). The low C18:1/high C22:1 mutant line L-1806, the high C18:1/high C22:1 mutant line L-482, the high C18:1/low C22:1 mutant line L-2890 and the low C18:1/very high C22:1 mutant line L-1630 were isolated after a chemical mutagen treatment of C-101 seeds (about 94 g C18:1/kg and 450 g C22:1/kg). The high C18:1/zero C22:1 line L-25X-1 was obtained by interspecific crosses of Ethiopian mustard with rapeseed and Indian mustard. Plants of lines L-2890×C-101, L-482×L-2890, L-1630×L-25X-1, L-1630×L-2890 and L-482×L-1806 were reciprocally crossed and F2 and the BC1F1 generations were obtained. Cytoplasmic effects were not observed in any of the crosses. The segregation pattern in F2 and BC1F1 populations differed in the crosses studied. The inheritance of C18:1 content in crosses segregating for this fatty acid was that expected for one (crosses between L-482×L-1806), two (L-2890×C-101) or three (L-1630×L-2890, L-1630×L-25X-1 and L-482×2890) loci. Oleic acid segregation indicated control of accumulation by two segregating genetic systems, one acting on chain elongation from C18:1 to C22:1 and the other involving desaturation from C18:1 to linoleic acid (C18:2). Accumulations of C18:1 and C22:1 were influenced by the same loci (M1, M2, E1 and E2), which control the chain elongation steps leading from C18:1 to C22:1. In addition, C18:1 was influenced by one additional locus (tentatively named OL) involved in control of desaturation of C18:1 to form C18:2. The genetic constitution of the parent lines would be OlOlE1E1E2E2m1m1m2m2 for L-2890, OlOlE1E1E2E2M1M1M2M2 for C-101, ololE1E1E2E2M1M1M2M2 for L-1630, OlOle1e1e2e2M1M1M2M2 for L-25X-1, ol1ol1E1E1E2E2M1M1M2M2 for L-482 and Ol1Ol1E1E1E2E2M1M1M2M2 for L-1806. Transgressive recombinants were obtained from the cross L-1630×L-25X-1, with about three-fold increase of the C18:1 content of the parents (>643 g/kg) and free of C22:1 content, which represent a high potential for commercial exploitation.

Field-average based recommendations have been a common practice for nitrogen (N) rate recommendations. The problem is that, even when the same amount of N fertilizer is applied at the recommended rate, yields differ from year to year, the result being poor use efficiency. Reduced fertilizer use efficiency can result in unnecessary costs to producers, especially with a likely price of US$ 1·10 per kilogram of N fertilizer anticipated within the next few years, largely due to rising oil and natural gas prices. It has been estimated that by the year 2025 the consumption of N fertilizer will increase by 60–90%, with two-thirds of this being applied in the developing world. In light of this, methods that increase N use efficiency and profitability of farms, while reducing environmental impact, are no longer simply commendable but required in developing countries. The present review assesses the temporal variability in winter wheat with respect to N nutrition and presents improved methods, including the calibration stamp (CS), N-rich strips (NRS) and ramped calibration strips (RCS) to overcome this variability. These methods can be used either as visual tools or along with NDVI handheld sensors for accuracy. Unlike the CS and NRS, the RCS method is designed to include more pre-plant N rates in strips to improve top-dress N estimation. Hypotheses as backgrounds to these methods have been developed and tested in the USA and Mexico. However, the simplicity of these technologies suggests that many farmers in both developed and developing countries can readily apply them.

The introduction and use of herbaceous legumes may contribute to agricultural intensification, especially in the context of sustainable crop and livestock production systems. In the context of evaluating different legume species for these systems in moist savanna zone of West Africa, the present study involved the evaluation of 46 accessions of Lablab purpureus (L.) Sweet between 2000 and 2002 at Samaru, Zaria in the northern Guinea savanna of Nigeria to identify accessions with the potential to contribute to grain or forage production and those with the potential for multiple use. Grain yields (0·6–2·4 t/ha) with a mean seed crude protein and phosphorus content of 25·3 and 0·46 g/kg, respectively, were obtained. Dry matter yields (leaf: 0·3–3·1, stem: 0·2–4·6, root: 0·03–0·3 t/ha) were produced between 40 and 140 days after planting. Within this same period up to 1152 kg shoot crude protein/ha, equivalent to 184 kg N/ha, were recorded for accessions. Ten accessions that may contribute to grain production, eight accessions that may contribute to forage production and six accessions with drought tolerance were identified. Some white-seeded accessions (Grif 1246, ILRI 4612 and PI 183451) with good grain and forage yield and high-protein content have the potential to provide more and higher quality food for people and feed for livestock. The observed potential to contribute to grain production for protein-rich food, feed for livestock and green manure for soil N improvement suggests lablab may be an acceptable legume option for use in cereal-legume-livestock systems in the moist savanna zone of West Africa.

Increasing grain legume yields via autumn sowing requires winter-hardy material. Forty-nine pea, 24 faba bean and 11 white lupin cultivars recently released by 29 breeding institutions worldwide were sown in autumn 2002 at Lodi (northern Italy) and Foggia (southern Italy) on two different dates at each location, with the objective of assessing the winter survival of species and cultivars, its consistency across locations and sowing times, its relationship with grain yield and various morphophysiological traits and the implications for selection. The winter seasons were representative for the sites and had 54 frost days and −7·3°C absolute minimum temperature in Lodi, and 8 frost days and −3·4°C absolute minimum temperature in Foggia. The species differed in optimal sowing time at each location. Mild winter temperatures, preventing a sufficient hardening against late frosts, led to higher proportions of plants killed over winter in Foggia than in Lodi (0·17 v. 0·12 for pea; 0·20 v. 0·16 for faba bean; 0·34 v. 0·11 for lupin). Variation in winter mortality was much larger within species than among species. Winter mortality and grain yield of cultivars were inversely correlated (r=−0·49, −0·43 and −0·74 for entry means over locations of pea, faba bean and lupin, respectively). The consistency across environments of genotype winter mortality, estimated by genetic correlations, was high across sowing times and low across locations for faba bean, moderate across sowing times and fairly low across locations for pea, and always fairly high for lupin. A visual cold tolerance score was always related to better winter survival. Winter survival tended to correlate with larger seeds in faba bean and lupin, and was associated with later flowering in lupin. A rosette-like winter growth habit (defined by lower height/number of leaves ratio of seedlings in January) was correlated with winter survival in all species (after partialling out the influence of seed size in faba bean and lupin). The optimal index of indirect selection for low winter mortality included the cold tolerance score, the seedling height/number of leaves ratio and the seed size for faba bean, the first two of these variables for pea, but only the first variable for lupin. The gain in predicted efficiency over direct selection was high for faba bean (29%) and modest for pea and lupin (⩽10%).

Cassava (Manihot esculenta Crantz) is one of the two most important food crops in sub-Saharan Africa. This area accounts for most of the root harvest worldwide, followed by Asia and Latin America – the centre of origin for Manihot species. In Africa and Latin America, cassava is mostly used for human consumption, while in Asia and parts of Latin America it is also used commercially for the production of animal feed and starch-based products. Cassava is regarded as a crop adapted to drought-prone environments, where cereals and other crops do not thrive, and it also grows well in poor soil. There are about 100 wild Manihot species, which provide an important genetic endowment for cassava breeding. Professional cassava breeding started in the 20th century and was spurred on by increasing population demands. The main breeding goals are high yield per unit area, particularly in marginal or pest-prone environments. The most notable results from cassava breeding are seen today in sub-Saharan Africa, where it has been transformed from a poor man's crop to an urban food, and in Southeast Asia, where it has changed from a subsistence crop to an industrial cash crop. Long-term research by many international and national partners has led to breeding high-yielding cassava cultivars that increased crop yields up to 40%. Manipulation of genes from wild species has led to new cultivars that resist prevailing diseases and pests, allowing the avoidance of large-scale famine in sub-Saharan Africa. Cassava improvement continues to tap genetic variation through conventional breeding (including the use of wild species) and biotechnology, because many pathogens still take their toll and occasionally epidemics affect farmer fields significantly. However, new sources of variation are needed to genetically enhance the nutritional quality of this important food crop in Africa and other areas in the tropics of the developing world.

A significant proportion of wheat (Triticum aestivum L.) yield increases achieved at the farm level in the past can be attributed to improved crop management practices. The important role of crop management practices in increasing the yield potential in wheat sustainably is illustrated with recent research findings from North Dakota. In the dryer regions, no-till and crop rotations significantly improve yield and protect the productivity of the soil. Intensifying management in the wetter regions through increased plant populations and by nitrogen timing did not increase yield in 2005 while fungicide applied at flowering for scab control did. In one study genotype interacted with management, with the most disease-tolerant genotypes producing the highest yield when treated with fungicides. Identifying and exploiting positive genotype by management interactions offers a potential avenue for increasing yield potential in wheat in the future. Identifying or developing crop management practices that hold potential for synergistically improving the yield of genotypes is a significant challenge. Imposing management practices that hold promise for improving yield sustainably on breeding material during the selection process has scope for identifying genotypes with greater yield potential at the farm level when these management practices are employed.

Identification of plant cultivars efficient for nitrogen (N) uptake and utilization may contribute to the improvement of crop yield potential in areas of low-N (LN) availability. Three cycles of full-sib recurrent selection were applied on a LN pool-yellow (LNP-Y) maize population to improve its level of tolerance to low soil N in the savannah ecosystem. The progress after three cycles of selection was evaluated for two years (2000 and 2001). The objectives of the study were to classify the cycles in relation to response to N levels under field conditions and to investigate the progress in selection for improved grain yield and other agronomic traits at two N levels, LN (30 kg N/ha) and high-N (HN, 90 kg N/ha). The experiment was conducted under field conditions at the LN screening site of the Institute for Agricultural Research, Samaru, in the northern Guinea savannah of Nigeria. The experimental design consisted of randomized complete blocks with three replications. The aboveground biomass and grain at harvest were analysed for total N content. The results indicated differences in plant population response to N levels. Mean grain yield ranged from 2·5 t/ha in cycle 1 to 2·7 t/ha in cycle 3 under LN and from 4·2 t/ha in cycle 1 to 4·3 t/ha in cycle 3 under HN. The observed gains were 4·8% per cycle under LN and 1·4% per cycle under HN. Nitrogen use efficiency (NUE) traits, viz. N uptake efficiency and N utilization efficiency were positively affected by selection. Gains for N utilization efficiency were 6·3% per cycle at LN and 9·1% per cycle at HN, while observed gains for NUE were 3·9% at LN and 1·4% per cycle at HN. However, N utilization efficiency was identified as the most important component of NUE for selecting cycles of selection in population development. Total N content and N utilization efficiency were significantly correlated with each other at LN, and had a significant, positive, direct effect on grain yield. Grain yield was positively correlated with N content and N utilization efficiency at both N levels. Also, a significant positive correlation was observed at LN between 300 kernel weight and N utilization efficiency. N utilization efficiency was correlated with ears/plant at HN and negatively correlated with anthesis-silking interval (ASI). The present study revealed that selection for improved productivity under LN stress conditions could be further enhanced by simultaneously selecting for high grain yield performance based on N utilization efficiency and on secondary traits, such as ears/plant, 300 kernel weight, and reduced ASI.

Since the 1970s, the delivered sugar yield per hectare has risen at an average annual rate of 0·111 t/ha, while the sugar yield in the official variety trials has increased at an average annual rate of 0·204 t/ha. These increases are usually considered to be the result of improvements in varieties and in beet agronomy. The present paper considers the possible impact of recent changes in climate on UK sugar yields by using the Broom's Barn Crop Growth Model and daily weather data collected over the last 30 years. Simulations of sugar yield using weather in eastern England since 1976 increased by an average annual rate of 0·139 t/ha, which accounted for about two thirds of the rate in the official variety trials. This increase was not an artefact of the accuracy of weather recording but it was, in part, accounted for by the trend to earlier sowing. Although it was not statistically significant, the earlier sowing trend was associated with an increase of 0·025 t/ha per year and was an indirect effect of the climate change. The annual deviations from these trends have not tended to become significantly bigger or smaller over the three decades. The model is not variety-specific, so it makes no allowance for variety improvements during the last 30 years. Clearly, varieties have improved so the implication must be that some of the changes in agronomy have tended to decrease the yields significantly. The changes in agronomic practice most likely to be responsible are the extension of the crop processing campaign, leading to greater post-harvest storage losses, and a decrease in the irrigated area.

In seeking better predictions of grain yield under light-limited conditions, shading was applied to field-grown winter wheat cv. Slejpner during each of five consecutive phases (canopy expansion, ear expansion, pre-flowering, grain expansion and grain filling). Absolute measures were taken of solar radiation and its effects on growth in three seasons, at a site where water and nutrient supplies were not limiting. Replicate mobile shades automatically occluded 0·80 of incident light when mean total solar radiation exceeded 250 J/m2 per s. Mean effects over seasons of shading on incident total solar radiation were −296, −139, −78, −157 and −357 MJ/m2 for the five phases respectively, and corresponding effects on shoot dry weight were −236, −184, −58, −122 and −105 g/m2. Estimated efficiency of radiation use after flowering was 1·2 g/MJ unshaded, tending to increase with shading. Shading in all phases reduced grain dry matter yield: mean effects over seasons were −106, −64, −61, −93 and −281 g/m2 for the five consecutive shading periods. Shading from GS31–39 increased mean maximum area of the two top leaves from 2700 to 3100 mm2 per leaf but, with fewer stems, canopy size remained unaffected. This and the next shading, from GS39–55, reduced specific leaf weight from 42 g/m2 by 4 and 3 g/m2 respectively, but effects on shoot dry weight were largely due to stem and ear. By flowering, stem weights, and especially their reserves of water-soluble carbohydrates, had partially recovered. Effects on yield of shading from GS31–39 were explained by a reduction in grains/m2 of 3070 from 26109. Shading from GS39–55 reduced grains/m2 by 4211 due to fewer grains per ear, whilst mean weight per grain increased in compensation. Shading from GS55–61 decreased grains/ear by 2·5. Shading from GS61–71 decreased ear growth and reduced stem weight, and at harvest resulted in 4·3 less grains/ear. Effects of the final shading from GS71–87 were fully explained by a reduction in mean dry weight/grain of 10·3 mg. Except for shading from GS71–87, source- and sink-based explanations of grain yield both proved feasible, within the precision of the measurements. Constraints to accurate comparison of source- and sink-based approaches are identified, and the implications for yield forecasting are discussed.

Sugar beet (Beta vulgaris L.) is one of the most important sugar crops worldwide. Despite the fact that sugar beet crop has high requirements for boron (B), the effect of B applications on seed yield and on seed quality is not known. A 2-year field study was conducted to determine whether soil and foliar B applications during anthesis increase seed set, final seed yield and improve seed quality of sugar beets. Boron solutions were applied at four rates (0, 245, 490 and 735 mg/l of B) as foliar applications and at two rates (1·5 and 3 kg/ha of B) as soil applications to field plots exhibiting no vegetative symptoms of B deficiency. Foliar B application increased the concentration of B in vegetative and reproductive tissues much more than soil application. In addition, foliar B application increased the seed yield by an average of 10% in the first year and by an average of 44% in the second year. The mean seed weight was affected by B application as it was increased in both years. The proportion of larger seeds (>5·00 and 4·5–5·00 mm) increased with increasing application of B. Moreover, seed quality was affected and the proportion of abnormal seedlings was decreased with B application. However, seed vigour was not affected by B application. These data indicate that foliar B application can improve seed yield and seed quality of sugar beet grown for seed production. However, the physiological basis of this effect remains unknown.

The present study was conducted to evaluate the effects of long-term administration of recombinant bovine somatotropin (rbST) on the regulation of body fluids, mammary blood flow (MBF) and other variables relevant to milk synthesis, in crossbred dairy cattle (0·875 of Holstein–Friesian (HF) genes and 0·125 Red Shindi (RS) genes. Ten first lactation, non-pregnant, animals were chosen and divided into the control and experimental groups of five animals each. Four consecutive measurements were carried out in each group beginning on days 45 (pre-treatment), 105, 165 and 225 of lactation. Animals that had completed 60 days of lactation were injected subcutaneously every 14 days with 500 mg of rbST (POSILAC, Monsanto, USA) in the experimental group, while animals in the control group were injected subcutaneously every 14 days with 800 mg of sterile sesame oil, without rbST, as a control. All animals were fed with rice straw treated with 50 g urea/l as the source of roughage in combination with a similar concentrate throughout the experiments. During the treatment periods, the daily dry matter intake (DMI) was numerically greater for rbST-treated animals than for control animals, while the relative values of DMI per kg body weight and water intake showed no differences.

Animals in both groups gained weight throughout the experiment with no significant differences between the groups. Animals receiving rbST for 45 days increased their peak milk yield from 13·4 kg/day per animal during pre-treatment to 15·9 kg/day per animal (18·7% increase) on day 105 of measurement and this peak yield was higher (19·5%) than those of control animals in the same period. Milk yields on days 225 in late lactation of both groups significantly decreased (P<0·05) in comparison with the early and mid-lactating periods. Over the course of the experiment, milk yield of the rbST-treated animals was significantly higher than those of the control animals (P<0·01). The administration of rbST significantly increased MBF (P<0·05) and mammary plasma flow (MPF) (P<0·01). The ratio of MBF to milk yield slightly increased as lactation advanced in both controls and rbST-treated animals. The administration of rbST significantly increased the absolute values of both plasma volume (P<0·01) and blood volume (P<0·05) when compared with the control animals. The control animals showed no significant changes in values of extracellular water (ECW) throughout the course of treatment periods. The rbST-treated animals increased in both the absolute values and the relative (proportion of body weight) values of ECW throughout the experiment (P<0·05). The estimated values of intracellular water (ICW) in both groups showed no significant changes during the course of treatments. There were no significant changes in the water turnover rate (WTO) and the biological half-life of tritiated water in different periods of lactation in both groups. The absolute values of total body water space (TOH) and total body water (TBW) were significantly greater in rbST-treated than control animals (P<0·05). The relative values of both TOH and TBW as a proportion of body weight of control animals decreased, while no alteration was apparent in rbST-treated animals during the course of treatments. These differences were statistically significant (P<0·05). The absolute values of empty body water (EBW) of the control animals showed no significant changes, while animals treated with rbST tended to increase in absolute values of EBW throughout the course of treatments. The effects of these differences were statistically significant (P<0·05). There were no significant changes in relative values of EBW during the course of treatments in both controls and rbST-treated animals. These data demonstrated that the rbST exerts its galactopoietic action in part through increases in TBW, EBW and ECW in association with an increase in MBF, which partitions the distribution of nutrients to the mammary gland for milk synthesis. During this long-term administration of rbST, the stimulant effect for milk yield was less in late lactation despite a higher MBF. The decline in milk yield during rbST treatment without fall in MBF in late lactation must be attributed to a local change within the mammary gland.

The objectives of the present study were to evaluate heterosis for grain yield and yield components in durum wheat, and to assess the prediction potential of amplified fragment length polymorphism (AFLP) based and agronomic trait based genetic distances (GD and MD, respectively) to F1 performance, mid parent heterosis (MPH), and specific combining ability effects (SCA) under well-watered and moisture stress conditions. Six parental genotypes with different responses to moisture stress and their 15 F1 crosses were evaluated for their responses to moisture stress conditions in a glasshouse. Some cross combinations showed significant MPH for grain yield and yield components. The expression of heterosis for grain yield was greater under moisture stress conditions than under well-watered conditions. Cluster analysis of the parental lines based on agronomic performance under stress conditions was similar to cluster analysis result based on AFLP marker profiles. F1 performance was strongly correlated to both SCA effects and MPH under both stress and well water conditions. The correlation between SCA and MPH was very high under both treatment conditions for all traits. Correlation between GD and MD was significant only under stress conditions. Positive correlation was found only for the association between GD v. F1 performance and GD v. SCA effects for harvest index (HI) under well-watered conditions. None of the correlations between MD and SCA effects were significant. The absence of association between GD and heterosis for yield and most agronomic traits implied that heterozygosity per se diversity is not a good predictor of heterosis or F1 performance under both well-watered and stressed conditions.