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The utilization of crop nitrogen (N) status as an in-season diagnosis tool for predicting N needs to maximize grain yield (GY) is a well-established concept in agronomy. However, a cross-species comparison including the characterization of yield components, grain number (GN) and grain weight (GW), to understand the physiological basis behind the GY-crop N status relationship is still missing. The main goal of this study was to perform a cross-species comparison for maize (Zea mays L.), rice (Oryza sativa L.), and wheat (Triticum aestivum L.) of the relationship between crop N status around anthesis as a GY and GY components prediction diagnosis method. A systematic literature search was carried out for these major field crops, the final dataset (comprising 629 observations) consisted of 15 publications including information on i) shoot biomass and plant N concentration or N nutrition index (NNI) values at anthesis, ii) GY, and iii) GN and/or GW. An analysis was conducted to assess the sensitivity (slope of the linear models) of GY, GN, and GW to changes in crop NNI status at anthesis. Notably, the crop N status at anthesis demonstrated a strong relationship between both GY (R2 between 0.66 and 0.93) and GN (R2 between 0.58 and 0.94) across all crops, with a slightly weaker relationship with GW (R2 between 0.30 and 0.83). Considerable uncertainty was observed on the GY and GN sensitivity (S) to N deficiency across all crops. Maize showed the greatest sensitivity of GY to NNI (S = 964 g m−2), with lowest sensitivity for wheat crop (S = 496 g m−2). Regarding GN, rice showed the greatest sensitivity to NNI (S = 23859 GN m−2), whereas maize was less sensitive (S = 2673 GN m−2). While maize exhibited a positive association between NNI and GW (although with considerable uncertainty), this relationship was less evident for rice and wheat crops. Our findings demonstrated that crop N status at anthesis is a better predictor of GY and GN than GW in maize, rice, and wheat. Maize showed the greatest range in observed values for relative GW relative to NNI, highlighting the impact of crop N status on GW determination. These findings contribute to improving the understanding of the importance of achieving adequate crop N status at anthesis as key aspect for yield formation, with implications for both breeding programs and the optimization of on-farm crop N management. • Crop N status at anthesis showed a strong relationship with grain number. • Maize showed the greatest sensitivity of grain yield to NNI at anthesis. • Rice showed the greatest sensitivity of grain number to NNI at anthesis. • Maize showed the greatest responses of grain weight to crop N status at anthesis. [ABSTRACT FROM AUTHOR]

Despite its global significance as a highly nutritious food, the critical period for grain yield and grain protein determination of quinoa has not yet been identified. This study aimed to determine the critical period of grain number, yield, and grain protein of quinoa in contrasting environments of South America. Five experiments were conducted in contrasting South American environments, including Argentina, Chile, Ecuador, and Peru, from latitudes 4°S to 39°S, and between 19 and 2165 m.a.s.l. Treatments consisted of the factorial combination of two quinoa cultivars (except in Peru, where only one genotype was used) and 4–9 shading treatments (50–85% shade) applied over 10–20 days throughout the crop cycle, depending on the site and the length of the crop cycle. We evaluated how GY, its components, and grain protein responded to the reduction of the source-sink ratio at different phenological stages. Yield of unstressed controls varied from 2.2 t ha−1 in Lima to 9.8 t ha−1 recorded in Valdivia. The grain protein concentration ranged between 12.6% in Lima and 16.8% in Loja. The most sensitive yield-determining period was between –26 and 445 °Cd from flowering across genotypes and environments. Grain protein concentration increased by up to 19% when the source of assimilates was reduced after anthesis; however, this was insufficient to compensate for the protein yield that was affected by the reduction in grain yield due to shading. The critical period for quinoa grain yield was determined throughout the flowering and grain-filling stages across genotypes and environments, mainly due to a decrease in both grain number and above-ground biomass. Identifying the critical period provides a useful target for breeding and management strategies to increase the quinoa crop yield. • Shading negatively affects grain setting and yield of quinoa, decreasing biomass and harvest index. • The critical period of grain yield is between –26 and 445 °Cd from flowering in quinoa. • Inter-Andean valley and see level genotypes have differences around the common critical period. • Grain weight is less sensitive to sequential shading than grain number. • Grain protein concentration of quinoa has variable sensitivity to shading. [ABSTRACT FROM AUTHOR]

Wheat is a crop of vital importance for food security. In contrast to the accumulated knowledge for yield determination, the effect of variations in the source/sink (S/S) ratio on grain quality, and its interaction with the genotype and fertilization level, have received little attention. This work aimed to analyze the incidence of S/S ratio changes during post-flowering on grain weight and commercial quality in bread wheat genotypes with contrasting baking aptitude, as well as to evaluate its interaction with early nitrogen-sulfur fertilization. It is hypothesized that modern wheat genotypes bred for high-yield and contrasting baking aptitudes differ in their responses to variations in the availability of assimilates during post-flowering. Rainfed field trials were carried out in the Humid Pampas of Argentina during two years. Six wheat genotypes belonging to different quality groups were used, to which manipulative S/S treatments in post-flowering (shading, defoliation, thinning, trimming) and different levels of nitrogen-sulfur fertilization were applied. Regressions between S/S ratio (growth per grain) and grain variables (grain weight, protein content per grain, protein concentration, and test weight) were analyzed. Grain weight responses ranged from − 42% to + 31% relative to control compared to variations in S/S ratio from − 81% to + 56%, varying with the year and genotype. Relative changes of grain weight and S/S ratio were linearly associated, showing differences in stability (slope range: 0.29–0.80) among genotypes (the lower the slope, the greater the stability). Protein content per grain increased linearly with increases in the S/S relationship only for fertilized crops with N and S. As expected, protein concentration decreased when the S/S ratio increased, while test weight was the opposite. Importantly, responses varied among genotypes and fertilization levels, regardless of baking quality group. Grain weight to S/S ratio after flowering relationships differed between bread wheat genotypes, even within the same quality group, while protein content stability did not differ significantly. Therefore, for the conditions of this study in high-yielding environments in the Humid Pampas, the different protein concentration responses were due to genotypic differences in grain weight stability against variations in assimilates availability during grain filling. Nitrogen-sulfur fertilization early at the crop cycle did not modify the grain weight responses to variations in the S/S ratio, although it increased their influence on the commercial quality parameters. These findings are relevant to genetic improvement for high yield that can increase the co-limitation by source and sinks, and the occurrence of farm adversities that restrict the source capacity during post-flowering. • The impact of source/sink ratio on wheat grain weight and their quality were assessed. • Genotypes differed in their grain weight stability to source/sink ratio changes. • Test weight was more stable for genotypes with the best baking quality. • N-S fertilization increased responses of protein percentage and test weight to source/sink ratio. [ABSTRACT FROM AUTHOR]

Grain weight is reported to be a relatively well conserved characteristic across spring barley ( Hordeum vulgare L.) crops that vary in grain number m −2 . Understanding the mechanisms that promote stability in grain weight is important to ensure that efforts to increase grain number beyond current high levels successfully increase yield without compromising grain quality. The aims of this study were to establish 1) whether post-anthesis grain abortion contributes to the stability of grain weight by helping match grain numbers to post-anthesis assimilate supply and 2) whether variations in post-anthesis assimilation per unit grain number affect the heterogeneity of grain weight. Field experiments were conducted in a high-yield potential environment for spring barley in 2011 and 2012. Crops were either shaded post anthesis (a 59% reduction in radiation incident on the crop) to reduce net carbon assimilation or grown unshaded. Grain growth was measured at different spikelet locations on the ear and on different shoots (main shoot and tillers) of the same plant. Shading crops from 14 days after anthesis until harvest maturity reduced yield by 19–20%, mean grain weight (MGW) by 12–16% and harvest index by 5–6%, but did not significantly affect grain number in either year. The magnitudes of these effects were considerably lower than the reduction in radiation imposed by shading suggesting some compensatory adjustment in radiation use efficiency or dry matter partitioning to grain after shading. The rate of grain filling was higher for grains in central spikelets than grains at distal or basal locations on the ear. Shading reduced the rate of grain filling to a similar extent (23–27%) at most locations evaluated on the ear, but had no effect on the duration of grain filling. In spite of the comparable effects of shading on grain growth across different spikelet positions and hierarchy of shoots, crops harvested after shading tended to have a more variable individual grain weight (larger interquartile range and coefficient of variation) than crops that were unshaded. The results show that post-anthesis grain abortion does not contribute to the stability of MGW in spring barley. Moreover, low levels of post-anthesis radiation in crops of large grain number m −2 (sink capacity) can increase heterogeneity of grain weight, which may have negative consequences for grain quality. [ABSTRACT FROM AUTHOR]

Availability of nitrogen and water are major constraints for crop yield, and their interactions are manyfold. Yield gap analysis in rainfed systems commonly uses water-limited yield potential (Y w ) as a benchmark; benchmarking against nitrogen-limited yield potential (Y N ) is less common. The aim of this study was to benchmark wheat yield against Y N in winter-rainfall regions of Australia. We established experiments, and sampled both farmers’ fields and National Variety Trials spanning wide ranges of soils, management practices, and water supply (seasonal rainfall + irrigation) from 153 to 759 mm in South Australia, and from 178 to 428 mm in Western Australia. We measured yield, quantified crop nitrogen nutrition index (NNI) at stem elongation, anthesis or both, derived boundary functions relating Y N and NNI, calculated yield gaps as the difference between Y N and actual yield, and explored the associations between yield gaps and environmental, crop and agronomic factors. In South Australia, NNI at anthesis ranged from 0.45 to 1.45 and yield from 0.9 to 8.9 t ha −1 ; in Western Australia NNI at stem elongation ranged from 0.27 to 1.16 and yield from 1.0 to 7.1 t ha −1 . Bi-linear boundary functions were fitted with a linear Y N – NNI phase up to a NNIx threshold (0.95 ± 0.134 in South Australia, 0.87 ± 0.145 in Western Australia), and a plateau reflecting yield potential (7.8 ± 0.38 t ha −1 in South Australia, 6.5 ± 0.52 t ha −1 in Western Australia). Similar bi-linear boundaries, with congruent NNIx (≈0.9), were found for grain number and shoot biomass at maturity. In South Australia, water supply explained 54% of the yield gap, which declined linearly from about 6 t ha −1 to zero with increasing water availability. Further, the yield gap correlated negatively with carbon isotope discrimination at anthesis, a direct measure of crop water status. In Western Australia, the direct association between yield gap and rainfall was weak, but there was an indirect agronomic link, where low seeding rate in low rainfall environments contributed to low biomass at stem elongation, which in turn explained a large part of the yield gap. In two out of five National Variety Trials, where the aim is comparing the yield of current and emerging varieties, crops were nitrogen deficient. This is a potential source of bias as some varieties were above and others below the NNIx threshold of nitrogen sufficiency. Supply of nitrogen in varietal comparisons needs attention. The approach advanced in this paper can be applied to benchmark yield against crop nitrogen status and identify causes of yield gaps, and for in-season quantification of crop nitrogen status to assist fertiliser decisions directly, or indirectly as a reference for spectral indices. [ABSTRACT FROM AUTHOR]

Grain weight (GW) is an important component of grain yield and quality of sunflower and the improvement of this trait has been proposed as an aim for breeding of this crop. There is strong evidence suggesting the pre-flowering period as key to determining GW in different crops; however, the key traits and mechanisms controlling GW during this phase are still largely unknown in sunflower. This study conducted a detailed survey of how the pre-flowering period determines grain growth dynamics by assessing the early developmental process during the growth of reproductive organs and the sensitivity of GW, grain number (GN) and grain oil concentration to different source–sink manipulations immediately before flowering. Two experiments were carried out under field conditions in two growing seasons. In Exp. 1 two sunflower oilseed hybrids contrasting in GW (Alybro and SG) were sown at the Experimental Station of the Universidad Austral de Chile in Valdivia (39°47′S, 73°14′W), Chile. In Exp. 2, the same hybrids plus a confectionery genotype (RHA) were evaluated in the Experimental Station where two source–sink treatments were performed: a control (without manipulation) and a shading treatment starting 16 days previous to anthesis, i.e. during the R2-R5 period. Crop development, average and individual GW, GN and oil concentration of grains were assessed at harvest. Also, flower and grain traits and their dynamics were measured from early reproductive stage (ovary at R3) to harvest in different grain positions from the capitulum (e.g., fresh and dry weight and dimensions of grains, pericarp and embryo and grain oil concentration). GW was significantly affected by genotype and shading treatments imposed at pre-anthesis, but no statistical effect of the lower source–sink ratio was found on GN. Contrary to GW, grain oil of oilseed genotypes was highly conservative under the source–sink reduction in our study. Positive associations were found between final GW and: ovary weight at R3, at anthesis (R5), ovary growth rate, grain dimensions and water content. Final GW also showed a linear association with ovary growth rate. This study is the first to evaluate the ovary weight from the early development stage and the ovary growth rate during the pre-anthesis period in sunflower and the effect of source reduction at pre-anthesis on grain oil concentration, supporting the importance of the maternal tissues on the setting of potential and actual GW in sunflower. [ABSTRACT FROM AUTHOR]

The use of physiological traits for indirect selection may help to increase wheat yield potential. Fruiting efficiency (FE, grain number per unit of spike dry weight at anthesis −SDWa-) may be an alternative to increase grain number per unit area (GN), but the possible cross-over genotype (G) × environment (E) interaction and trade-off with SDWa and grain weight (GW) may limit its usefulness. The present paper aimed to determine (i) the degree of G × E interaction of FE at plot, main stem and tiller levels, (ii) the relationship between GN and FE, and (iii) the possible trade-off between FE and (a) SDWa, and (b) GW. Three FE contrasting genotypes (B11 and B19 – high FE, and B2002 – low FE) were grown under different Nitrogen (N) availability at sowing [(i) low – Ni: ca. 50 kg N ha −1 ; (ii) middle −130 kg N ha −1 and (iii) high −200 kg N ha −1 ). Two other treatments were applied within the 200N: (iv) late sowing, i.e. delaying sowing 30 days in relation to optimum date (200N + LS) and (v) shading the canopy during stem elongation (200N + SH). The FE showed G × E interaction (year × genotype and genotype × treatment) but it only explained 13.4% of its variation. The environment (year) had similar impact than the genotype, explaining both ca. 38% of FE variation (19% each). The FE of tiller spikes was higher than that of main stem spikes, but the difference among cultivars was maintained. Thus, canopies of the same genotype with different proportion of main stem and tiller spikes may present different FE value at plot level. Nevertheless, a high correlation (r = 0.82, p < 0.0001) and a close 1:1 relationship was observed between FE at plot level and FE in main stems, for all treatments and cultivars, suggesting that sampling the main stem spikes represents the FE at plot level in dense canopies. A G × E cross-over interaction was observed when the sowing was delayed one month (200N + LS) from the optimum date because B19 reached anthesis later than B2002, exploring higher heat stress index (°Ch > 27 °C) around anthesis, which reduced FE. The correlation of GN with FE was high and significant (r = 0.74, p < 0.00001) for all treatments and for a wide range of SDWa values (from 90 to 188 g m −2 ). The B19, selected as a high FE genotype, showed higher GN than B2002 (selected as a low FE genotype) under all treatments, while B11 (also of high FE) showed similar or higher GN than B2002, depending on treatment. Thus, despite the G × E interaction, the genotypes with higher FE had more GN under a wide range of environments. Nevertheless, the SDWa and GW were negatively correlated with FE (for SDWa r = −0.73 p < 0.005, without considering 200N + SH; and for GW r = −0.48 p < 0.01 for all treatments or r = −0.75 p < 0.08 for genotypes only). Then, special attention should be given to SDWa and GW when selecting for higher FE in a breeding program. [ABSTRACT FROM AUTHOR]

Annual crops accommodate environmental variation through grain number, whereas grain weight is more stable. Grain number is determined in a species-specific window which has been established for many crops, but not for oat. Field trials were established at two sites in southern Australia and in one site in southern Chile where successive, single 14-d shading periods were applied from crop establishment to maturity to identify the developmental window when the crop is most responsive to stress. Three oat varieties were compared in Australia (Mitika, Williams and Wintaroo) and two in Chile (Mitika and Yallara). Unshaded controls yielded from 327 g m −2 in Australia to 747 g m −2 in Chile. The overall pattern of yield response to time of stress was similar to that of wheat; it spanned the period from stem elongation (GS31) to about 10 days after anthesis. In line with theory, most of the yield response was mediated through response in grain number; further, the two environments in Australia where reduction in grain number in response to stress shortly before anthesis was larger, individual grain weight increased with shading. Grains per panicle was more responsive to stress than panicles per m 2 , in contrast to other cereals. The critical period is often assumed to be species-specific. However, our limited comparison of varieties suggests that there might also be varietal differences in oat. Interaction between time of shade and variety was significant for harvest index in all locations. Hence, we propose genotype-dependent response to time of stress is worth exploring. [ABSTRACT FROM AUTHOR]

In order to study the effect of duration of the vegetative period (sowing to floral initiation) on potential yield, sister spring wheat semi-dwarf cultivars, Yecora and Cajeme, the latter having an extra vernalization sensitive allele (Vrn-A1v) and a photoperiod sensitive one (Ppd-D1b), were grown at 4–5 sowing dates over 5 years under irrigation and high fertility in northwest Mexico (latitude 27°N). In the earliest sowings (late Oct-early Nov) Cajeme had a 20 day longer vegetative period; this delay decreased steadily to 8 days in the latest sowings (mid-late January); anthesis date for Cajeme was, respectively, 17 and 6 days later. Relationships to minimum temperature levels in the vegetative phase strongly suggest that this sowing date by cultivar interaction arises largely because of the difference in vernalization alleles in an environment where there is limited vernalizing cold. Cajeme produced a greater maximum number of shoots, more spikelet nodes per spike, greater green area index, and greater above ground dry matter at anthesis and at physiological maturity. However Cajeme yielded no more than Yecora, even when yield was plotted against anthesis date, tending to have fewer grains/m 2 . A similar conclusion was reached when grains/m 2 were related to preanthesis photothermal quotient, and grain weight to grain filling mean temperature: both cultivars responded similarly although Cajeme had slightly fewer grains/m 2 and heavier kernels, thus weather around flowering dominated determination of these yield components. Some other yield components were also slightly, but significantly, affected by cultivar in a manner independent of flowering date and weather. Thus Cajeme had a significantly higher spike dry matter at anthesis and a significantly lower fruiting efficiency of Cajeme (73.8 versus 84.2 grains/g spike dry matter). It is suggested that the latter was a consequence of the longer vegetative period leading to greater tillering, poorer tiller survival and a more competitive preanthesis canopy, causing poorer floret survival in grain-bearing spikes. The excessive tillering may have been exaggerated by supplying all nitrogen fertilizer at sowing. [ABSTRACT FROM AUTHOR]

Wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.) crops are exposed to warm nights during their growing seasons and this trend is unlikely to change. The aim of this work was to evaluate the effect of higher post-anthesis night temperatures on field-grown crop yield, focusing on final grain weight determination. Experiments combined: (i) two well-adapted crops with similar phenology: bread wheat and two-row malting barley, under (ii) two temperature regimes: ambient and high night temperatures from 10 days after anthesis to physiological maturity during (iii) two contrasting growing seasons in terms of radiation and temperature: late sowing in 2011 and early sowing in 2013. The night temperature increase (ca. 4.1 °C) was achieved using purpose-built heating chambers placed on the crop at 7 pm and removed at 7 am every day during the heating period. Across growing seasons and crops, the average minimum temperature during that period ranged from 14.3 °C to 21.9 °C. Thousand grain weight was reduced by ca. 3% per °C of night temperature increase, similarly for wheat and barley, causing a grain yield reduction of ca. 4% per °C. An accelerated development under high night temperatures led to a shorter effective grain filling period, reducing the final grain weight. The lack of consistent impact on source availability between crops and seasons, measured as senescence and stem water soluble carbohydrates, as well as a similar impact in magnitude and direction on individual grain weight for different grain positions along wheat or barley spikes, suggest that the negative effects of warm nights on grain weight were directly related to processes within the grain itself. [ABSTRACT FROM AUTHOR]

Maize yield has to be increased in the next decades in order to satisfy world demand. This increase has to be achieved in a scenario of climate change particularly characterised by heat stress. Several agronomic and genetic strategies for increased tolerance to high temperatures will be necessary. Some results in other crops showed interactions between high temperature stress and nitrogen (N) availability. To the best of our knowledge, this interaction has not been tested in maize. Therefore, the aim of this study was to explore, under field conditions, whether the magnitude of yield penalty imposed by elevated canopy air temperature around flowering or during early grain filling is affected by N availability. In particular we aimed to (i) quantify the magnitude of yield losses by heat stress around flowering and during early grain filling, (ii) determine whether N fertilisation affects these magnitudes, and (iii) identify whether the effects are indirect (through affecting growth) or directly on the grain set and/or grain growth capacity. Four field experiments were carried out during four consecutive years in NE Spain. The treatments consisted in a factorial combination of one or two hybrids, two or three levels of N fertilisation and three temperature conditions. The temperature treatments consisted of a control (plots grown under natural temperature throughout the growing season) and two treatments in which the temperatures of the canopy were increased in the field for relatively short periods. All experiments were well watered to avoid water stress. The elevated canopy air temperature treatment only increased the maximum temperature in a relatively small magnitude (mean daily temperature was increased at the ears height by c. 1 °C each day of treatment). However, yield penalty imposed by heat stress was in general very noticeable and dramatic when the treatment included the critical period for grain number determination, around silking. The damage was much stronger in the long- than in the short-cycle hybrid. Exposing the plants to elevated canopy air temperature during the critical period reduced harvest index, from values of around 46% in unheated conditions to 20% under elevated canopy air temperature, being the reduction higher under N200 than under N0 fertilisation treatments. As far as we are aware, we showed for the first time in maize grown in field conditions, that the losses in yield in response to elevated canopy air temperature treatment were magnified by the N availability. The effect of N on emphasising the penalties seemed not to be a direct effect of this nutrient but and indirect effect through affecting growth. The effect was through affecting the capacity of the plants to set grains and to a lesser extent to allow grain weight to be maximised; and it was independent of any (potentially additional) effects on either uncoupling anthesis and silking or on pollen amount and viability. [ABSTRACT FROM AUTHOR]

The properties of individual grain weight, protein concentration and protein composition contribute to grain quality of wheat. They are known to be affected by genetics, environment and crop management. This paper reports these properties in two dryland field experiments comparing cultivars with similar yield but with contrasting grain weight and number. A large-seeded cultivar, Baviacora, and a small-seeded cultivar, H45, were managed with different nitrogen (N) fertilizer applications and grown in seasons with different rainfall. The aim is to suggest strategies to produce wheat grain of consistently high quality for specified markets, with either pre-harvest or post-harvest management. Individual grain weight and protein concentration varied throughout the spikes of the cultivars and responded to crop management and environment. Protein concentration within a spike was closely correlated with individual grain weight, increasing by 0.05 ± 0.006% per mg of additional grain weight, independent of cultivar or position of grains on the spike. Grain protein composition was related to protein concentration of individual grains but was not as sensitive to individual grain weight. Larger grains were associated with less glutenin per unit of protein, partly offsetting the increase in protein concentration with grain weight. Unextracted polymeric protein (%UPP) was unrelated to grain weight but was negatively related to grain protein concentration in Baviacora. If found to be general, the within-spike relationships between individual grain weight, and the concentrations of grain protein, glutenin and %UPP offer promise for improving grain segregation and post-harvest processing to produce grain of closely defined quality from an unprocessed harvest sample. • Grain protein amount and composition varied with genotype, environment and management. • Within spikes, protein concentration was positively correlated with grain weight. • Glutenin concentration varied with protein concentration of individual grains. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigated the relationships between yield components considering phenotypic plasticity. [•] Grains per m2 and spikes per m2 were coarse regulators while all components may be responsible for fine regulation of yield. [•] We showed that the rankings of responses of yield components depend on the nature of the driver, i.e. genotype or environment. [•] Strong trade-offs between components were found for small changes in yield or in grains per m2 for both environmental and genetic factor. [•] For large changes, trade-offs were weaker, but much stronger for components of yield than of grains per m2, particularly for genetic drivers. [Copyright &y& Elsevier]

Highlights: [•] We studied the responsiveness of source–sink manipulations in wheat and barley grown at four different environments. [•] Grain weight was significantly reduced by shading the whole canopy, but the effect was smaller by shading only the leaves. [•] Spike photosynthesis seemed to have been down-regulated in the controls, as it was increased by shading the leaves. [•] In most cases, significant amounts of water soluble carbohydrates remained unused in the stems at maturity. [•] Wheat and barley seemed not to be source-limited during grain filling, unless are subjected to an extremely severe stress. [ABSTRACT FROM AUTHOR]

Abstract: Previous yield gains in wheat have been achieved through increased expression of grain number per unit area, while fruiting efficiency has also been shown to explain improved grain number. However, combining a high grain number and weight in the same genotype is a difficult task in practical breeding. This study evaluated the progeny of a cross between two elite parents that contrast in grain number and grain weight, as a way to better understand how the two desired traits might be combined to achieve a significant boost in yield. The two parents are both high biomass elite spring wheat lines that achieve high yield through contrasting strategies: Bacanora achieves high grain number with a high density of relatively small spikes. Weebil has a lower density of larger spikes in which larger grain size is expressed. The specific objectives of this research were: (i) to evaluate grain yield performance of DH lines and parents over two seasons, (ii) to identify promising physiological traits explaining high yield performance and (iii) to determine whether these traits are also expressed at the low plant densities. Two experiments were carried out under field conditions in southern Chile where the highest yield potential of wheat has ever been recorded. In Exp. 1 the performance of the 105 spring wheat DH lines, their parents and a Chilean spring cultivar (Pandora-INIA) with similar phenology were assessed together. Results showed that it is possible to increase yield potential by combining high grain number and grain weight, thereby reducing the trade-off between both components. 42 and 50% of the DH lines showed transgressive segregation in S1 and S2, respectively. 3 and 4% of the DH lines yielded between 15,000 and 16,000kgha−1. Grain yield was highly correlated with above-ground biomass (R 2 =0.78, p <0.0001 in S1 and R 2 =0.77, p <0.0001 in S2) and grain number (R 2 =0.69, p <0.0001 in S1 and R 2 =0.71, p <0.0001 in S2), whereas no correlation was found with either harvest index or grain weight. In Exp. 2, the high-yielding DH lines selected from Exp. 1 showed on average 45% higher grain yield (p <0.01) than the Chilean checks. Differences in yield between the DH lines and the checks were explained by grain number m−2, which was closely related to grain number spike−1 and fruiting efficiency. The latter trait was in line with faster post-anthesis spike dry matter accumulation, explaining in turn the higher radiation use efficiency of the selected DH lines recorded during this period. When comparing yield and its components at different plant densities, grain yield and both main yield components showed strong correlations between environments as a result of increased expression of grains spike−1 (p <0.001) under low plant density that was able to offset the reduction in spike number m−2 (p <0.001). [Copyright &y& Elsevier]

Abstract: Yield differences among wheat cultivars and its responsiveness to resource availability are usually related to grain number per m2, and further increases in grain number are required, but now beyond differences in time to anthesis and plant height (that are mostly optimised in traditional growing regions). The objective of this paper was to determine and quantify differences in yield physiology between different modern well adapted durum wheats grown in contrasting conditions (in addition we also tested if a higher amount of resources due to removal of competition could affect yield through the same determinants to nitrogen (N) availability). Four experiments were carried out during two growing seasons (2008–09 and 2009–2010); all in all under eight different growing conditions (Gc1–Gc8). In the first season four different modern cultivars were used and in the second season we selected the two highest-yielding cultivars, which differed in their responses to N in terms of spike fertility. Yield was closely related to biomass and N uptake due to both growing conditions and genotypic effects in all experiments. The existence of variation among modern cultivars in these yield determinants is relevant as further increases in yield must be achieved beyond further increases in partitioning. Yield differences among cultivars were based on their differences in grains per m2 or average grain weight depending on which cultivars were compared. Overall grain number was related to spike dry weight at anthesis, and no evidences were found for a direct involvement of N in grain number determination, beyond the general effect of N availability on spike dry matter. However, this overall effect was mainly driven by growing conditions whilst differences between genotypes seemed associated with either spike dry weight at anthesis or fruiting efficiency, which varied significantly between cultivars. Interestingly, grain weight was consistently higher in the cultivars with lower fruiting efficiency than in cultivars maximising the number of grains set per unit of spike dry weight at anthesis suggesting a constitutive component for the commonly reported negative relationship between grain weight and grain number. In conclusion, the main differences in yield between modern, well adapted wheats were related to their biomass and N uptake and to the sink-strength during post-anthesis, being this strength increased either by having more grains or grains of potentially greater size, depending on the specific cultivar and as a consequence of a trade-off between fruiting efficiency and grain size. [Copyright &y& Elsevier]

Abstract: CIMMYT hexaploid spring wheat (Triticum aestivum L.) germplasm has played a global role in assisting wheat improvement. This study evaluated four classes of CIMMYT germplasm (encompassing a total of 273 lines), along with 15 Australian cultivars (Oz lines) for grain yield, yield components and physiological traits in up to 27 environments in Australia''s north-eastern region, where terminal drought frequently reduces grain yield and grain size. Broadly-adapted CIMMYT germplasm selected for grain yield had greater yield potential and improved performance under drought stress, being up to 5% greater yielding in High-yielding (mean yield 429gm−2) and 4–10% greater yielding than adapted Oz lines in Low-yielding environments (mean yield 185gm−2). Whilst maintaining statistically similar harvest index and spikes m−2 compared to broadly-adapted Oz lines across all environments, sets of selected CIMMYT lines had greater canopy temperature depression (0.18–0.27°C), dry weight stem−1 (0.20–0.37g), increased grains spike−1 (0.8–3.4 grains), grain number m−2 (ca. 20–800 grains), and maturity biomass (56–83gm−2). Compared to selected Oz lines, broadly-adapted CIMMYT lines had a smaller reduction in Low compared to High-yielding environments for these traits, especially dry weight stem−1, such that CIMMYT lines had ca. 25% and 10% greater dry weight stem−1 than the Oz lines in Low- and High-yielding environment groups, respectively. Broadly-adapted CIMMYT germplasm also had slightly higher stem water soluble carbohydrate concentration at anthesis (ca. 6mgg−1), which contributed to their higher grain weight (ca. 0.5mggrain−1), and maintained an agronomically appropriate time to anthesis and plant height. Thus current CIMMYT germplasm should be useful donor sources of traits to enrich breeding programs targeting variable production environments where there is a high probability of water deficit during grain filling. However, as multiple traits were important, efficient introgression of these traits in breeding programs will be complex. [Copyright &y& Elsevier]

Abstract: In water-saving rice culture, yield is unstable because spikelet number per unit area and grain weight fluctuate according to water availability. In this study, we investigated the factors that determine grain weight in aerobic culture. We grew four rice varieties in non-puddled, unsaturated (aerobic) soils with a soil water potential at 20-cm depth kept above −60kPa and in continuously flooded culture in two years. We found a significant variety×water interaction in grain weight in 2009: weights under aerobic culture were 6% and 13% larger than under flooded culture in Sasanishiki and IRAT109, respectively, versus 4% and 10% smaller in Habataki and Takanari. There was no significant variety×water interaction in grain weight in 2010. Sink activity (grain sucrose synthase activity) and source capacity (biomass production and nonstructural carbohydrate content in vegetative tissue) per plant during ripening were higher under aerobic culture than under flooded culture in both years. However, an excessive increase in spikelet number per unit area in Takanari under aerobic culture in 2009 reduced the source capacity per spikelet and single husk size, decreasing grain weight. In 2010, frequent soil drying under aerobic culture during the late reproductive period (around 20 days preceding heading) reduced single husk size, thereby decreasing grain weight. We found that sink activity and source capacity per plant could be both higher under aerobic culture during the ripening period, producing larger grain weight at a soil water potential above–40kPa at a 20-cm depth relative to those under flooded culture. In contrast, greater drying under aerobic culture during the late reproductive period reduced single husk size, thereby reducing grain weight. [Copyright &y& Elsevier]

Abstract: Foliar diseases are the main biotic restriction reducing yield in wheat crops affecting both, grain number and/or grain weight, depending on developmental stage at which infection occurs (pre- or post-anthesis, respectively). Grain weight reductions due to foliar diseases were widely reported in the literature mostly associated with decreases on radiation interception during the grain filling period. However, different evidences in wheat showed variations on grain weight responses when fungicide was applied during the grain filling period, probably associated with the timing of fungicide application or with the amount of available resources per grain set when fungicides are applied. The present study was designed to determine the causes of grain weight reduction due to foliar diseases complex (including leaf rust, Septoria leaf blotch and tan spot) in wheat crops growing under contrasting agronomic and environmental conditions (i.e. different years, locations, cultivars and N supply). The experiments were carried out during 4 years under field conditions in different locations of Argentine and France. Five different commercial wheat cultivars were sown on early and late sowing dates; and two contrasting N availability and two fungicide treatments (protected and unprotected) were applied. Grain number was not affected by foliar diseases as their appeared after anthesis. Grain weight was strongly, poorly or not affected by foliar diseases and was not associated individually with both, the sink size and the source size. However, when the grain weight response due to fungicide application was plotted against the healthy area absorption per grain (HAAG), a significant negative association (r 2 =0.81; p <0.0001) was found for the Argentine experiments. When the HAAG was corrected by the grain weight potential (HAAGW) all experiments conduced in Argentine and in France fit well to a common negative linear regression (r 2 =0.74, p <0.0001) for the relationship between grain weight variation and HAAGW demonstrating that grain weight potential is an important feature to consider in diseases control programs. Foliar diseases forced the crop to use the accumulated reserved increasing the utilization rate of the water soluble carbohydrates (WSCUR), depleting as a consequence the water soluble content at physiological maturity (WSCPM) in all experiments. The association between WSCUR and the healthy area absorption per grain corrected by grain weight of healthy crops (HAAGW) suggest that foliar diseases in wheat cause source limitation, forcing to the crop to use the WSC reserve which could be insufficient to fill the grains previously formed. [Copyright &y& Elsevier]

Abstract: Several studies have been conducted to evaluate the response of crops, especially temperate cereals, to different source–sink ratios during grain filling. However, there is much less information about temperate legumes and even less work comparing the two. The objective of this study was to evaluate the response of both grain yield and grain nitrogen concentration of wheat (Triticum aestivum L.), narrow-leafed lupin (Lupinus angustifolius L.) and pea (Pisum sativum L.) to similar source reduction during grain filling. Two field experiments were conducted in a high yielding environment of Southern Chile. In experiment 1 wheat and narrow-leafed lupin were grown for two consecutive years. Experiment 2 evaluated wheat and pea on two sowing dates. In both experiments a reduction in the source–sink ratio was imposed by using black nets that intercepted 90% of the incident solar radiation from the commencement of the linear dry matter accumulation to physiological maturity. Grain yield was differentially (p <0.01) decreased by the source reduction in lupin (98%), wheat (63%) and pea (26%). Given that these experiments were carried out in a high yielding environment, the higher response of wheat relative to previous studies supports the hypothesis that the higher the yield potential, the higher the source sensitivity of this crops during the grain filling period. On the other hand, source reduction positively affected (p <0.05) grain nitrogen concentration in wheat (66%) and pea (18%) but negatively affected lupin (40%). The higher sensitivity of grain yield compared to that of grain nitrogen yield was the cause of the positive effect of the lower source–sink ratio recorded in wheat and pea. In contrast, source shortage in lupin decreased grain nitrogen concentration probably as result of the quick response of grain growth to source limitation. The contrasting sensitivities of lupin, wheat and pea to source reduction during grain filling prevent us to see grain yield and quality response of these crops as separate groups, i.e. temperate cereals vs. temperate legumes. [Copyright &y& Elsevier]

Abstract: We present a simple generic framework to quantify source–sink relationships during grain filling, by using a determinate growth function which has a unique property, namely being able of explicitly describing the time for the end of a growth process. This model framework was applied to analyze these relationships in plants of six wheat (Triticum aestivum L.) genotypes grown in pots in climate-controlled greenhouses under two temperature regimes (day/night: 20/15 and 25/20°C). The function accurately described the sigmoid pattern of grain growth (sink activity), as its modified form did for the reversed sigmoid shape of flag-leaf area (source capacity), during grain filling. The six genotypes differed significantly in grain number as well as in grain yield, ranging from 54 to 81 grains and from 2.67 to 4.52g DM per culm, respectively, when grown at 20/15°C. Biomass and grain yield were significantly reduced by a rise of 5°C. Grain nitrogen contents raised from 2.1 to 2.6% as a consequence of less carbon accumulation resulting in lower grain weights at the high temperature. On average, a rise of 5°C in temperature reduced the duration of grain growth by 12 days (>30%), and increased the growth rate from 1.32 to 1.67mggrain−1 d−1 (20%). Genotypic differences in grain-filling duration were also larger than in rate of grain growth. The genetic variation in the flag-leaf area duration (a proxy for the capacity for intercepting radiation and photosynthesis) was positively associated with sink size. Model analysis showed that whether or not the timing for the cessation of grain filling and for the end of post-anthesis source activity was synchronized depended on temperature. The quantitative approach yielded parameters that characterize genotypic differences of post-anthesis source and sink capacity in responding to environmental variables. [Copyright &y& Elsevier]

Abstract: In wheat, the ability to store and remobilise large amounts of stem water soluble carbohydrates (WSC) to grain constitutes a desirable trait to incorporate into germplasm targeted to regions with frequent terminal drought. The main aim of this paper was to examine the relationships between WSC storage, grain number and grain weight across several environments. A small set of recombinant inbred lines (2–4) contrasting in stem WSC were grown in six field trials where water availability, sowing date and/or N level were manipulated, with line yields ranging from 400 to 850gm−2 across experiments. Biomass, N and WSC concentration (WSCc, mgg−1 dry weight) and amount (WSCa, gm−2) were monitored. A resource-oriented area-based model [Fischer, R.A., 1984. Growth and yield of wheat. In: Smith, W.H., Bante, S.J. (Eds.), Potential Productivity of Field Crops Under Different Environments. International Rice Research Institute, Los Baños, pp. 129–154] and intrinsic rates of organ growth were used to investigate the consequences on grain number of potential competition between spike and stem around flowering. Early sown irrigated trials allowed consistent genotypic discrimination for WSCc and WSCa. High WSC lines had similar or higher yields compared to low WSC lines. High WSC lines had consistently lower grain number m−2 linked to a lower number of spikes and stems m−2, higher individual grain weight under irrigated or more limited conditions, and individual stems with less structural biomass. The changes in plant type associated with the high WSC phenotype, mainly fewer stems and a high individual grain weight, may contribute to its moderate yield advantage despite the lower grain number m−2. A model based on resource capture per unit area around flowering was not sufficient alone to explain the differences between lines in grain number m−2. We propose that linking a resource-based model with additional understanding of controls of crop morphology would improve the prediction of differences in yield components in related genetic material. [Copyright &y& Elsevier]

Abstract: Bread wheat has been frequently characterised as sink-limited during grain filling but the degree of sink-limitation could vary with the contribution of breeding in increasing the number of grains per unit land area. This hypothetical change in the level of sink-limitation due to breeding has been insufficiently documented. Two source–sink manipulation experiments under field conditions with three released cultivars and an advanced breeding line representing important steps in wheat breeding in the Mediterranean area of Spain were conducted in order to quantify whether genetic improvement of grain yield in Mediterranean wheat modified the source–sink balance during grain filling, and how it affected grain weight and post-anthesis photosynthetically active radiation intercepted by the crop (IPAR) and radiation use efficiency (RUE). Average grain weight of control and trimmed spikes during grain filling was not significantly affected by halving the number of growing grains in the two oldest cultivars, but it was significantly increased in the most modern line, and had an intermediate response in the intermediate cultivar. In those cases in which a certain degree of source-limitation during grain growth occurred the magnitude of the response reflected a co-rather than a source-limitation. Considering grains from different positions within the spikes the smaller (distal) grains responded more markedly than the larger (proximal) grains. No differences in post-anthesis IPAR were found between the trimmed and control sub-plots for any of the genotypes. However, trimming the spikes reduced post-anthesis RUE, a fact corroborated by a simultaneous reduction in leaf net photosynthetic rate at noon. It seems that bread wheat breeding has tended to reduce the strength of the sink-limitation during post-anthesis even under Mediterranean conditions, and consequently the most modern line presented a sort of co-limitation. [Copyright &y& Elsevier]

Abstract: Low phytic acid (LPA) crops have recently been considered as a potential way to combat nutritional and environmental issues related to seed phytic acid phosphorus (PA-P). Although, a number of LPA mutant lines have been developed in various crops, they are often featured with lower grain yield and seed viability compared with wild type (WT) parents. We recently developed several LPA mutant lines in rice with PA-P reductions varying from 33.8% to 63.6%. In this study, the performance of grain yield and seed viability of these mutants were investigated. Four of the five mutant lines had 12.5–25.6% reductions in grain yield compared to the corresponding WT parental lines. The reduction in grain weight, varying from 5.4% to 10.7%, was found to be the main causative factor of yield reduction. Similarly, LPA mutants had inferior seed viability to their corresponding WT parent varieties; all mutant lines had a significantly lower simplified vigour index (seed germination rate×seedling dry weight) than their parents, with reductions of 7.8–26.3%, although some mutant lines had similar germination rates as their WT parents. The two mutant lines, which had similar germination rates as their WT parent, however, had significantly lower field emergence rates. More pronounced differences of simplified vigour index were observed after artificial aging treatments between four LPA lines from their WT parents, implying that LPA rice seeds were more susceptible to storage than WT. The yield and yield-related traits of F2 plants and F3 lines from three crosses were evaluated; the results showed that while LPA was associated with significantly lower grain yield and grain weight than WT sibs, there were also LPA plants and lines that out-performed WT controls. These results implied that the negative effect of LPA mutations on grain yield might be reduced or minimized through cross and selection breeding. The implications of these findings were discussed with regard to LPA rice breeding and potential commercial production. [Copyright &y& Elsevier]

Abstract: In temperate cereals are commonly accepted that determination of grain number (GN) and grain weight (GW) scarcely overlap during the crop cycle. However, the assumption that GW is determined exclusively after anthesis needs to be critically reviewed in the light of reports published over the few years where temperature treatments imposed before anthesis decreased GW of bread wheat. Although these evidences suggest that both GW and GN could be affected by environmental conditions before anthesis little is known about the effect of pre-anthesis temperature on these two main yield components in wheat, barley and triticale at field conditions. In addition, the effect of temperature on GW and GN at different stages prior to anthesis has been scarcely evaluated. The objectives of the current study were: (i) to evaluate the overall response, and specific differences, of GN and GW to pre-anthesis temperature, and (ii) to study the effect of different timings of high temperature at pre-anthesis on GN and GW in wheat, barley and triticale. Three fully irrigated field experiments were carried out in three successive seasons. At each season, a wheat, barley and triticale high yielding cultivar was evaluated at three temperature regimes: control, and two timings of heating before anthesis. During the first and second seasons, the timings of heating were booting-anthesis and heading-anthesis. In the thirst season, the timings were beginning of stem elongation-booting and booting-anthesis. Plots were arranged in a split-plot design with three replicates, where the main plot was assigned to thermal regime and the sub-plots to crop species. To apply heat, transparent chambers equipped with thermostatically controlled electric heaters were used. The thermal regime was controlled by sensors connected to a temperature regulator and recorded using data loggers. Temperature within the chambers was stable across developmental stages, crops, and seasons; it averaged 5.5°C higher than air temperature. Thermal treatments consistently reduced grain yield (p <0.05), the magnitude of the effect ranged between 5 and 52%. The highest effect was found when temperature increased during stem elongation (yield decrease: 46%), lowest when treatments were imposed during heading-anthesis (15%) and intermediate for treatments imposed during booting-anthesis (27%). Most effects of thermal treatments on yield were due to parallel effects on GN. However, thermal treatments significantly (p <0.05) decreased GW during the three seasons. The most effecting treatment on GW was when the crops were heated during the B-A period, i.e. GW decreased up to 23%. [Copyright &y& Elsevier]

Abstract: Multi-location data collected over 30 years in Finland on major cereal crops (spring barley, oat and wheat, and winter wheat and rye) provide an opportunity to characterise variation, interrelation and relative importance of the grain yield determining components, grain number per square meter (GNO) and single grain weight (SGW). In addition to evaluating differences among cereal crops in yield determination, changes among different age groups (AG) were compared. Field experiments were carried out in 1970–2001 at 25 locations in Finland. Grain yield was recorded (at 15% moisture) and SGW (mg) and GNO (numberm−2) determined. Frequencies of different GNO and SGW combinations were analysed for all crops and component means in different yield groups as well as among four AGs. In most cases GNO dominated SGW, representing the major yield component determining grain yield. GNO was highly responsive to favourable growth conditions. The change in GNO was especially high when recurrent, relatively low yield groups were compared, while at higher yields the role of SGW became increasingly important, but did not exceed that of GNO. The degree of GNO domination varied according to crop. Increased grain yield in spring oat and winter rye was associated with higher numbers of set grain, while spring barley and winter wheat responded to yield favouring conditions also through higher SGW. Despite GNO dominated SGW due to its responsiveness to growing conditions, its role in yield improvement was not obvious when the entries (n ≥30) were classified into four AGs. Improvements in grain yield derived from AG were associated with crop-specific GNO and/or SGW changes. [Copyright &y& Elsevier]

Abstract: This study explored whether the average grain weight of wheat tends to be reduced when grain number is increased due to either competition or, to a consistent increase in the relative proportion of grains of smaller weight potential. Three field experiments considering environmental, genetic and environmental×genetic effects on yield and its main components were analysed during the 2003/2004 growing season in two different locations within the Mediterranean area of Catalonia, Spain. The relationship between grain weight and number of grains per unit land area was analysed for both the average of all grains (AGW) and for grains in specific positions of the main-shoot spikes: proximal (CPg) and distal (CDg) grains of central spikelets, and proximal grains of the near apical (APg) and near basal (BPg) spikelets. The proportional contribution of grains per spike for the different grain positions and the relative contribution of spikes per m2 made by the main shoot or tillers were also examined. In the three experiments, AGW was reduced when grain number was increased due to genetic and/or environmental factors. However, the slopes of the straight-lines that represented the negative relationship between grain number and grain weight were lower (less negative) and less significant for CPg (b =−0.20, P >0.20), CDg (b =0.06, P >0.20) and BPg (b =−0.21, P >0.20) than for AGW (b =−0.40, P <0.05). The proportional contribution of distal grains and tiller spikes (both with relatively light grains) were directly related to grain number increases. Therefore, as grain number increased there was a higher proportion of grains of low potential weight. Thus, the average grain weight was concomitantly reduced when grain number increased by increasing the proportion of “small grains” in the canopy independently of any competitive relationship between growing grains. [Copyright &y& Elsevier]

Abstract: In order to quantify the effects, at different stages during grain filling, of alternating day/night high temperature regimes on sunflower grain yield and quality, heads were exposed to high temperatures during 7 or 6 days starting either 10–12 days after anthesis (daa, HT1), 18 daa (HT2) or 24 daa (HT3). Also, heads were exposed to high temperatures for periods of 2, 4 or 6 days in each of HT1 and HT2. Temperatures covered a range of mean daily grain temperature of 20–40°C and peak grain temperatures (i.e., those prevailing during the central 5h of the daylight period) of 26–45°C. High temperature stress for periods of 4 days or longer produced significant (p <0.05) reductions in grain yield and grain quality. Early (HT1) exposure to stress reduced yield by 6%/°C above a mean grain temperature threshold of 29°C; later (HT2+HT3) exposures reduced yield by 4%/°C above a threshold of 33°C. These reductions in yield were attributable to reductions in unit grain weight at all positions (periphery, intermediate, central) on the head, and an increase in the proportion of very small (10–30mg) grains, termed half-full (HF) grains in this paper. In both full and HF grains, stress in either HT1 or HT2 reduced final pericarp weight, associated with fewer number of cell layers and thinner cell walls in the schlerenchyma. High temperatures reduced both the rate and duration of oil deposition in the grain, with the greatest effects being found with early (HT1) exposures. The unsaturation (oleic acid/linoleic acid) ratio of oil from mature grain was altered only when exposure to heat stress overlapped with the cessation of deposition of storage lipids. The effects of duration and intensity of heat stress on relative (to control) grain yield and oil content could be reasonably summarized using a linear response to cumulative hourly heat load calculated with a base temperature of 30°C. We conclude that: (i) 4 days of alternating day/night temperatures resulting in mean daily grain temperatures of >30°C can reduce sunflower grain yield and quality; (ii) the magnitude of these effects is strongly dependent on the timing of exposure and their nature on the grain growth processes active at the time of stress; and (iii) an hourly heat load (base=30°C) provides a useful integrative estimator of the effects of exposure to heat stress on grain yield and oil content for a given phase of grain filling. [Copyright &y& Elsevier]

Brief periods of high temperature have been shown to reduce grain weight and quality in temperate cereals but the nature of sunflower grain growth and oil quality responses to exposure to high temperature are unknown. We examined these issues by exposing the capitulae of plants of cv. HA89 growing at 25 °C to temperatures of ca. 35, 37 and 40 °C for seven consecutive days in each of the three different intervals during grain filling. Final grain weight was reduced (−40%, on average) by temperatures >35 °C during early grain development due to a reduction of the duration of grain growth. Oil grain percentage was also reduced (−30%) by temperatures >35 °C, largely through an increase in the pericarp:embryo ratio, although with extreme temperatures a reduction of embryo oil percentage was also observed. Final oil composition proved to be sensitive to the timing of heat stress. The fatty acid pattern was strongly modified during exposure to heat stress but final oil composition was only altered by exposure to stress in the period from 19 to 26 days after anthesis (daa). Early heat stress allowed partial recovery of oleate desaturase (ODS) activity in the post-stress period, but this recovery did not occur when the ending of exposure to high temperature took place close to the ending of the oil accumulation process. We conclude that the period from 12 to 19 daa showed the greatest sensitivity to heat stress regarding embryo and grain weight responses, whereas the period of greatest sensitivity for oil quality was from 19 to 26 daa. A clear step-change in response to temperature was found, indicating a threshold for grain growth responses at 35 °C. Brief periods of heat stress produced sunflower grain with a lower weight, a greater percentage of pericarp, a lower oil content and an altered fatty acid composition, and hence, of lower commercial quality. [Copyright &y& Elsevier]

• We measure yield and protein of shaded lentil in southern Australia and Chile. • The most sensitive period was pod emergence, between 50–126 °Cd after flowering. • Grain number and biomass accounted for most of the variation in yield. • Grain protein concentration varied according to a bi-linear model. • Protein yield tracks grain yield and is partially buffered by late season protein. Lentil is a cool season grain legume produced primarily in the Mediterranean and temperate regions of the world where water and heat stress in critical developmental windows constrain yield. The effect of stress on yield depends on the timing, intensity and duration of stress; here we focus on timing relative to phenological development. To determine the critical period for grain yield and grain protein, we compared unshaded controls and crops exposed to sequential 10–14 d shading periods using two locally adapted varieties at Roseworthy, south-eastern Australia, and Valdivia, southern Chile. Yield of unstressed controls varied from 1 t ha−1 at Roseworthy to 7 t ha-1 at Valdivia, and grain protein from 22.0 % at Valdivia to 27.6 % at Roseworthy. Irrespective of growing conditions, the most sensitive period was at 50–126 °Cd after flowering, around pod emergence. Grain number and biomass accounted for most of the variation in yield. Grain protein concentration varied according to a bi-linear model, with minor reduction (<10 %) before a developmental threshold (i.e. flowering at Valdivia, ∼ 200 °Cd after flowering at Roseworthy) and a linear increase after the threshold. Protein yield tracked grain yield, but the increased grain protein concentration partially buffered the effect of post-flowering stress. [ABSTRACT FROM AUTHOR]

• Source reduction after the beginning of flowering increased seed weight in different windows for winter (15–30 DAF) and spring rapeseeds (0–15 DAF). • Seed weight increased 33 % for winter and 39 % for spring rapeseeds in response to the source-sink reduction. • Seed oil changed very little in response to source reductions after flowering. • Seed protein concentration showed a negative association with oil concentration. • Seed protein concentration was associated positively with seed weight and negatively with seed number. Breeding heavier seeds while maintaining seed number has been proposed as an effective strategy to improve oil crop production. Recent studies assessing rapeseed source-sink (S-S ratio) reduction after flowering suggest a window in the early seed-filling period that can compensate, either partially or totally, for a decrease in the number of seeds. However, little evidence has been reported in relation to the key window for seed plasticity in rapeseed. Furthermore, such studies have only assessed spring rapeseed genotypes and there is a lack of information on winter rapeseed. This study aims to elucidate the occurrence of a narrow window when seed plasticity is greatest, which is hypothesized to occur during the early stages of seed filling after the beginning of flowering in both winter and spring rapeseed genotypes. To asses this hypothesis, two winter and two spring rapeseed hybrids were evaluated under three S-S ratio treatments in two experiments performed in field conditions in Valdivia, Chile. The winter hybrids Trust and Mercedes were assessed under different nitrogen levels, and the spring hybrids Lumen and Solar were assessed using two sowing dates. S-S ratio treatments in both rapeseed genotypes consisted of a control without S-S ratio manipulation, a reduced S-S ratio from the beginning of flowering [BBCH 61] to 15 days after flowering (DAF) and a reduced S-S ratio from 15 to 30 DAF. The S-S ratio was reduced by shading the crop with black nets to intercept 75 % of the incoming solar radiation. Shading treatments decreased seed yield relative to the control between 13 and 42 % for the winter genotypes and from 23 to 44 % for the spring genotypes. The negative effect of shading on seed number under both S-S reduction timings explains the seed yield reduction. Interestingly, different windows of time for seed weight plasticity were found in response to the lower S-S ratio for winter and spring genotypes (i.e., 15–30 and 0–15 DAF, respectively). In the winter-type genotypes, seed weight increased between 28 and 33 % under the 15–30 DAF shading treatment, while seed weight in spring-type genotypes increased from 15 to 39 % during the 0–15 DAF treatment. Seed weight change was almost negligible outside of the sensitivity window as this trait increased only 2% at 0–15 DAF in winter-type genotypes and 7% at 15–30 DAF in spring-type genotypes, across treatments. In parallel, the S-S reduction decreased seed number by 23.6 and 40 %, at the 0–15 and 15–30 DAF treatment, respectively. The study showed statistical differences for seed oil and protein concentration across treatments, but both quality traits remained highly stable to the S-S reduction and showed similar behavior in winter and spring rapeseed types. Seed oil concentration changed little while seed protein concentration was more sensitive to seed weight response. The findings of the present study suggest that seeds per silique and seed weight are determined by the plant assimilate S-S ratio ; therefore, seed number and seed weight determinations overlap as has been demonstrated in other crops like wheat, barley, sorghum and sunflower. [ABSTRACT FROM AUTHOR]

• Oat panicles are highly plastic structures. • Primary and secondary grain numbers are highly correlated across panicle sizes. • Panicle size increases with an increase in leaf number and leaf size. • Seed rate did not affect the weight of primary or secondary grains. The objective of the current investigation was to study the plasticity of the oat panicle together with associated changes in leaf area and grain weight as affected by seed rate and tiller order. Plants (cv. Husky) were sampled from autumn sown seed rate experiments (100, 200, 300, 400, 500 seeds/m2) in 2016 and 2017 after anthesis and separated into their component tillers. The number of primary, secondary and tertiary grains on each whorl of the panicle of each tiller were counted, green leaf area per tiller was measured and, in 2017, the number of green leaves per shoot in addition to leaf length and leaf width were measured. At grain maturity, plants were sampled from three treatments (100, 300, 500 seeds/m2) and separated into their component tillers. The number of primary, secondary and tertiary grains on each whorl were counted and weighed. Primary and secondary grain numbers on all mainstem whorls except the uppermost whorl increased significantly as seed rate decreased, the largest changes being on the bottom whorls. There were also significant increases in green leaf area per stem as seed rate was decreased due to increases both in the number and size of leaves. Grain numbers per whorl decreased significantly with increasing tiller order but green leaf number per stem and leaf area per grain increased with increasing tiller order. The number of secondary grains per panicle was tightly correlated with the number of primary grains per panicle irrespective of seed rate or tiller order. Seed rate had no significant effect on the weight of primary or secondary grains but primary and secondary grain weights were significantly greater on the first tiller compared to the mainstem and second tiller. The oat panicle is a highly plastic organ, the plasticity of the oat panicle contributes to yield stability. Grain weight stability is preserved across a wide range of panicle sizes by changes in leaf area per stem and by the highly stable nature of the relationships between primary and secondary grain numbers and between primary and secondary grain weight. [ABSTRACT FROM AUTHOR]