Increased Sink Size Research Articles

Effect of high temperature during the late seed filling period on green stem disorder in soybean

ContextGreen stem disorder (GSD) in soybeans is a condition wherein delayed leaf and stem maturation at harvest negatively affects harvest efficiency and seed quality. Biotic and abiotic stresses promote GSD, which is mediated by sink limitations at the flowering and pod setting stages. Previous studies have suggested that high-temperature stress promotes GSD. However, the critical growth period and its mechanisms have not yet been elucidated. ObjectiveThe present study investigated the relationship between temperature and GSD severity in growth chambers and fields. MethodsThe study was conducted in two parts. First, the effects of high temperature on GSD (30/25 ℃, day/night) at different growth stages were analyzed in growth chambers. Second, field experiments were conducted to verify the relationship between temperature during the late seed-filling period and GSD severity. Three near-isogenic lines (NILs) with different combinations of maturation genes, E1, E2, and E3, were cultivated on three sowing dates (June, July, and August) for two years. ResultsHigh temperatures in the late seed-filling period significantly promoted GSD severity, whereas high temperatures in the early seed-filling period had no effect on GSD. Sink size did not decrease with high-temperature treatments. The field experiment in 2019 also revealed a positive correlation between GSD severity and mean temperature during the late seed-filling period, whereas mean temperature before the seed-filling period showed no correlation with GSD. Temperatures during the late seed-filling period accounted for GSD suppression in the late-maturation genotype and late sowing dates, whereas the early maturation genotype had an unknown mechanism to promote GSD. On the other hand, in the field experiment in 2020, ratio of source ability to sink size became lower than in 2019 because of higher solar radiation during sowing to R1 period increased sink size. As a result, in 2020, the effect of temperature relatively low compared to the effect of source-sink ratio. ConclusionThe findings indicate that high temperatures during the late seed-filling period promoted GSD. Sink limitations were not the cause of the phenomena. Annual variation of GSD occurrences could be explained by considering effects of both temperature and solar radiation in the specific growth stage. The late seed-filling period corresponds to autumn during the soybean cropping season. Therefore, the phenomena revealed in this study could be responsible for the GSD occurrences promoted by global warming in soybean fields. ImplicationsThis study facilitates selecting appropriate soybean cropping seasons and cultivars for each area to avoid GSD occurrence.

Comparison of Heat Sinks in Back-End of Line to reduce Self-Heating in 22FDX® MOSFETs

This work compares the effect of different heat sink dimensions in the back-end of line (BEOL) on the self-heating (SH) parameters. To assess the self-heating (SH) parameters, the RF characterization technique is employed, which involves measuring S-parameters across a broad frequency spectrum. In addition to the standard device without a sink, two sinks of different dimensions, both connected to the gate, are considered: one smaller and one bigger in size. We experimentally demonstrate lower self-heating as the sink size increases. By using a smaller and a larger sink, a mean reduction of 4.7% and 8.9% in thermal resistance is observed, showing greater SH reduction with increasing sink size, which is also verified from comparison with previous works. The impact of the sinks on RF figures-of-merit (FoMs), namely the cutoff frequency fT and maximum oscillation frequency fmax is investigated. fT is seen to degrade stronger due to increased gate capacitance whereas fmax degradation is limited because of reduced gate resistance.

Effects of nitrogen fertilization for bud initiation and tiller growth on yield and quality of rice ratoon crop in central China

Rice ratooning is an ancient technology, known as harvesting twice after one sowing. In recent years, ratoon rice has drawn much attention and been widely practiced by farmers in central China because of its advantages in saving labor and increasing profit. For ratoon crop (RC), nitrogen (N) application for promoting bud initiation (Nbud) and for promoting regenerated tiller growth (Ntiller) are two common N management practices. However, it is still obscure about their effects on grain yield and quality of RC. Field experiments were conducted to compare the effects of Nbud (75 kg N ha−1 application at 12 days after heading of main crop, MC) and Ntiller (75 kg N ha−1 application at 2 days after harvesting of MC) on the grain yield and quality of RC in 2018 and 2019. Compared to Nbud, Ntiller had an evident and positive effect on grain yield, head rice percentage (HRP) and chalkiness degree (CD) of RC. Averaged across years, Nbud and Ntiller increased grain yield of RC by 5.5 % and 30.5 %, respectively. Moreover, Ntiller improved grain quality with an increase of 10.5 % in HRP and a decrease of 10.2 % in CD. Ntiller significantly increased sink size like spikelets m-2, and source ability including leaf area index, leaf N content, and crop growth rate in ratoon crop. The positive effect of Nbud on grain yield of RC was positively correlated with the increase in panicles m-2, but negatively correlated with the panicles m-2 of MC. Nbud has no effect on stubble dry weight, and significantly increased stubble N concentration, but significantly decreased stubble non-structural carbohydrate concentration at maturity in the main season. Overall, our results indicated that nutrient status of straw and panicle number in MC affected the roles of Nbud on RC yield, and more attention should be paid on Ntiller in future RC production.

Effect of foliar spray of kinetin on the enhancement of rice yield by elevated CO2

AbstractRising atmospheric CO2 concentrations stimulate photosynthesis and productivity of C3 plants such as rice (Oryza sativa L.), a phenomenon known as the CO2 fertilization effect (CFE). Previous studies have shown that a greater sink capacity (e.g. grain number, or grain size) enhances the CFE on rice yield and that cytokinin is involved in the sink capacity; however, the direct involvement of this phytohormone in the CFE remains unclear. In this study, we tested whether exogenous application of kinetin improved the CFE of cultivars with different sink sizes (Koshihikari, japonica, with small sink; Takanari, indica with large sink) using a free‐air CO2 enrichment experiment on a rice paddy. We hypothesized that kinetin increases the sink size and thereby enhances the CFE, particularly for the cultivar with a smaller sink. Elevated CO2 (200 µmol/mol above ambient concentration) increased grain yield by 11.4%, averaged across two cultivars. Kinetin significantly improved the CFE in Takanari from 11.2% to 19.2%, but not in Koshihikari. The enhancement of the CFE by kinetin in Takanari appeared through the increased sink size resulting from a greater panicle density. In contrast, kinetin did not increase panicle density or sink size in Koshihikari and failed to enhance the CFE. We therefore conclude that sink size improves CFE on rice yield, and that kinetin could increase sink size, but the effect is cultivar dependent.

DEP1 affects rice grain weight and quality at different spikelet positions

AbstractGrains at different positions on rice panicles differ greatly in weight and quality, but few studies have focused on the effect of dep1 that influences panicle morphology and grain number on grain weight and quality at different spikelet positions and under different backgrounds. To clarify this, we compared spikelet characteristics and grain quality in the superior spikelets (SS) and inferior spikelets (IS), as well as sink‐, source‐ and flow‐related traits between NIL‐dep1 (AKI‐dep1 and LG5‐dep1) and NIL‐DEP1 (AKI‐DEP1 and LG5‐DEP1) under the Akitakomachi (AKI) and Liaogeng5 (LG5) backgrounds. The grain weight and quality in SS did not significantly differ between NIL‐dep1 and NIL‐DEP1 under the two backgrounds. However, the effect of dep1 on grain weight and quality in IS varied with background. AKI‐dep1 significantly decreased the grain weight, processing quality, and eating and cooking quality in IS compared with AKI‐DEP1, possibly due to poor grain filling and the lack of an adequate source supply and vascular system to fully meet the increased sink size. With the exception of appearance quality, the grain weight and quality of IS of LG5‐dep1 were similar to LG5‐DEP1, mainly due to the enlarged vascular system and similar grain filling rate and source supply. We concluded that the varied effects of dep1 on grain weight and quality under the two backgrounds could be attributed to differences in grain filling and source−sink−flow relationships.

Accelerated grain-filling rate increases seed size and grain yield of recent naked oat cultivars under well-watered and water-deficit conditions

Increased seed size has greater contribution in yield improvement in recent naked oat (Avena sativa L. subsp. nudisativa) cultivars than cultivars derived from landraces. However, the underlying grain-filling mechanisms associated with seed size and grain yield in naked oat have received limited study. Two field experiments and a pot experiment compared grain-filling mechanisms, seed size and grain yield of ten naked oat cultivars, including old (landraces, released before 1950s) and new (released since 2008) cultivars. In both well-watered and water-deficit conditions, the new cultivars had higher grain yields, higher thousand kernel weights (TKW) and higher grain numbers per spike, but fewer fertile spikes per unit area or per plant, and no significant differences in grain number per unit area or per plant, than old cultivars. The findings in both the field and pot experiments demonstrated that increased grain-filling rate, rather than duration, enhanced seed size (TKW) and grain yield in the new cultivars. The increased grain-filling rate in a new cultivar was associated with higher rates of endosperm cell division and higher number of endosperm cells, compared to that in an old cultivar, but there were no significant differences in starch synthesis enzyme activity and ABA concentration between the old and new cultivars. As a result of current breeding and selection, the increased the grain yield of new cultivars of naked oat is primarily due to increased seed size (increased sink size) arising from a greater number of endosperm cells per grain, and not because of increased enzyme or phytohormonal activity. The larger seed size is important in the production of oats for food rather than for forage.

Wheat grain number and yield: The relative importance of physiological traits and source-sink balance in southern Australia

Grain number (GN) is determined by spike growth rate (SGR), fruiting efficiency (FE) and the duration of spike growth period (Ds). However, these three traits are not independent of each other and therefore quantifying their relative contribution to GN is important for improving yield potential. This study aimed to model GN as a function of SGR, FE and Ds in bread wheat and investigate the relative importance of these three traits in determining GN. A large number of commercial varieties, elite wheat breeding lines, and a Multiparent Advanced Generation InterCross population were evaluated for GN, SGR, Ds, and FE in six Australian environments in 2014 and 2015. The model explained 43–98% of the variation in GN in individual environments and 88% of the variation in GN across the six environments. The percentage of GN variance explained by the model was significantly higher than those explained by correlating GN to individual traits. The relative importance of the contribution of the three traits to GN was different and ranked as SGR > FE > Ds. The negative correlation between FE and spike dry weight at anthesis (SDWa) appears to be spurious, suggesting that there was no causality between high FE and low SDWa and vice versa. Thus, FE can be used as an independent trait to increase GN in addition to SGR and Ds. We also investigated if the wheat crop had enough source to fill the increased sink size in the southern Australian high rainfall environment. The source-sink balance analysis indicates that the available source, consisting of concurrent photosynthetic assimilate and stored water-soluble carbohydrate at anthesis, was sufficient to fill the established sink but no surplus assimilates were available to fill a larger sink in southwestern Australia. However, the opportunity to increase yield potential by further increasing grain number might exist in south-eastern Australia environments.

Continuous applications of biochar to rice: Effects on grain yield and yield attributes

Biochar is considered as a beneficial soil amendment for crop production. However, limited information is available on the effects of continuous applications of biochar on rice. In this study, a fixed field experiment was conducted in the early and late rice-growing seasons from 2015 to 2017. Grain yield and yield attributes with a widely-grown rice cultivar Zhongzao 39 were compared, with and without applications of biochar in each season. The results showed that grain yield initially decreased with biochar applications in the first three seasons due to decreases in grain weight and harvest index. Although there were further relative decreases in grain weight and harvest index for rice that was supplied with biochar in the fourth to sixth seasons, grain yield was increased (by 4–10%) because of increases in sink size (spikelets per m2) and total biomass. The increased sink size in rice whose soil had been supplied with biochar in the fourth to sixth seasons was achieved by increasing panicle size (spikelets per panicle) or number of panicles, or both. Our study suggests that the positive effects of biochar application on rice yield and yield attributes depend on the duration of biochar application. Further investigations are needed to determine what are the soil and physiological processes for producing yield responses associated with ongoing applications of biochar. Also, it should be evaluated the performance of biochar application combined with other management practices, especially those can increase the grain weight and harvest index in rice production.

Progressive integrative crop managements increase grain yield, nitrogen use efficiency and irrigation water productivity in rice

It is a major challenge to achieve the goal of increasing grain yield, nitrogen use efficiency (NUE) and irrigation water productivity (IWP) in cereals. This study investigated if progressive integrative crop management technology in rice (Oryza sativa L.) could improve agronomic and physiological performances, and consequently, increase grain yield, NUE and IWP. A japonica rice cultivar and an indica-japonica hybrid rice cultivar were grown in the field, with five crop managements including an unfertilized 0N treatment (0N), local farmer’s practice (LFP), integrative crop management (ICM) 1–3 ((ICM1, ICM2, and ICM3)). The results showed that, when compared to LFP, the ICM could not only increase grain yield, NUE and IWP, but also improve agronomic and physiological performances. Both ICM1 and ICM2 increased economic benefit. The progressive effect on the yield, NUE, IWP, and agronomic and physiological performance was obvious with the progressive introduction of single cultivation technology. The ICM increased sink size (total number of spikelets), percentage of productive tillers, leaf area index and duration, crop growth rate, non-structural carbohydrate accumulation and remobilization, leaf photosynthetic rate, root dry weight and length, root oxidation activity, root bleeding, and zeatin and zeatin riboside content in roots and leaves. The results suggest that the integrative and optimized crop management could achieve the dual goal of increasing grain yield and resource use efficiency through improving agronomic and physiological performances, especially increases in sink size and shoot and root growth, leading to higher grain yield, NUE, and IWP.

Agronomic and Physiological Performance of Rice under Integrative Crop Management

Agronomic and physiological performances of a crop are closely associated with the yield and resource use efficiency. This study investigated if an integrative crop management (ICM) in rice (Oryza sativa L.) could improve agronomic and physiological performances and, consequently, increase grain yield, nitrogen use efficiency (NUE), and water use efficiency (WUE). A japonica hybrid rice cultivar was field‐grown in 2012 and 2013. Three treatments were conducted: no N application, local high‐yielding cultivation method (LHY), and ICM. The ICM consisted of the adoption of three practices: increased plant density, optimized N management, and an irrigation regime of alternate wetting and moderate soil drying. The ICM substantially increased sink size (total number of spikelets per m2), percentage of productive tillers, root oxidation activity, leaf area duration, non‐structural carbohydrate accumulation in the stem, and zeatin (Z) and zeatin riboside (ZR) content in roots and leaves. On average, the ICM increased grain yield by 18 to 19%, agronomic NUE (kg grain yield increase per kg N applied) by 67 to 70%, and WUE (grain yield per unit water consumed) by 27 to 28% over the LHY. The results suggest that the ICM could achieve the dual goals of increasing grain yield and resource use efficiency, and improved agronomic and physiological performances, especially increased sink size and enhanced root and shoot activities during the middle and late growth periods, contributed to high grain yield, NUE, and WUE in rice.

Genetic mechanisms underlying yield potential in the rice high-yielding cultivar Takanari, based on reciprocal chromosome segment substitution lines.

BackgroundIncreasing rice yield potential is a major objective in rice breeding programs, given the need for meeting the demands of population growth, especially in Asia. Genetic analysis using genomic information and high-yielding cultivars can facilitate understanding of the genetic mechanisms underlying rice yield potential. Chromosome segment substitution lines (CSSLs) are a powerful tool for the detection and precise mapping of quantitative trait loci (QTLs) that have both large and small effects. In addition, reciprocal CSSLs developed in both parental cultivar backgrounds may be appropriate for evaluating gene activity, as a single factor or in epistatic interactions.ResultsWe developed reciprocal CSSLs derived from a cross between Takanari (one of the most productive indica cultivars) and a leading japonica cultivar, Koshihikari; both the cultivars were developed in Japan. Forty-one CSSLs covered most of the Takanari genome in the Koshihikari background and 39 CSSLs covered the Koshihikari genome in the Takanari background. Using the reciprocal CSSLs, we conducted yield trials under canopy conditions in paddy fields. While no CSSLs significantly exceeded the recurrent parent cultivar in yield, genetic analysis detected 48 and 47 QTLs for yield and its components in the Koshihikari and Takanari backgrounds, respectively. A number of QTLs showed a trade-off, in which the allele with increased sink-size traits (spikelet number per panicle or per square meter) was associated with decreased ripening percentage or 1000-grain weight. These results indicate that increased sink size is not sufficient to increase rice yield in both backgrounds. In addition, most QTLs were detected in either one of the two genetic backgrounds, suggesting that these loci may be under epistatic control with other gene(s).ConclusionsWe demonstrated that the reciprocal CSSLs are a useful tool for understanding the genetic mechanisms underlying yield potential in the high-yielding rice cultivar Takanari. Our results suggest that sink-size QTLs in combination with QTLs for source strength or translocation capacity, as well as careful attention to epistatic interactions, are necessary for increasing rice yield. Thus, our findings provide a foundation for developing rice cultivars with higher yield potential in future breeding programs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0295-2) contains supplementary material, which is available to authorized users.

Clustered QTL for source leaf size and yield traits in rice (Oryza sativa L.)

Improvement of plant type plays an important role in super-high yield breeding in rice (Oryza sativa L.). In the present study, a set of backcross recombinant inbred lines derived from a cross of 9311 and Zhenshan97, both elite indica hybrid parents, were developed to identify quantitative trait loci (QTL) for flag leaf size, panicle and yield traits. Forty-seven QTL for 14 traits were detected in common in the two environmental trials, of which nine genomic regions contained clustered QTL affecting plant type traits and yield traits. Four co-localized QTL on chromosomes 1, 6, 7 and 8 involving QTL for flag leaf size (flag leaf length, width and area) contained the QTL for yield traits such as panicle weight (PW) and secondary branch number (SBN), and in all cases alleles from 9311 increased source leaf size and were associated with increased sink size and yield (SBN and PW). Using a subset of overlapping substitution lines for the QTL region on chromosome 1, the QTL were validated and narrowed into a 990 kbp interval (RM3746–RM10435) with pleiotropic effects on flag leaf size, PW, SBN and spikelet number per panicle. These QTL clusters with large effects on source leaf size and yield-related traits provide good targets for marker-assisted breeding for plant type improvement and high-yield potential in rice.

Evaluation of yield performance in rice near-isogenic lines with increased spikelet number

Rice yield potential is determined by the balance between sink size and source capacity. To clarify the factors that limit yield in temperate japonica cultivars, we compared the yield performance of Sasanishiki, a temperate japonica cultivar, with those of three near-isogenic lines (NILs) of Sasanishiki with introgression of quantitative trait loci (QTL) derived from a high-yielding indica cultivar, Habataki: qSBN1, which increases the number of secondary rachis branches; qPBN6, which increases the number of primary rachis branches; and a pyramid line that combines these two QTLs. NIL ( SBN1), NIL ( PBN6), and NIL ( SBN1 + PBN6) produced 28–37%, 9–16%, and 62–65% more spikelets per panicle than Sasanishiki, respectively. However, the NILs with increased spikelet number per panicle did not increase grain yield significantly, because compensation is taken place among different yield components. The pyramid line nevertheless had 4–12% higher yield than Sasanishiki due to greater translocation of carbohydrates from stem to panicle. There was no difference in carbohydrate accumulation before heading or in biomass production among Sasanishiki and the three NILs. The results indicate that increasing sink size does not substantially improve yield in Sasanishiki, which lacks sufficient substrate supply to fully satisfy the increased sink demand that results from the spikelet-number QTLs.

The addition of gibberellic acid to auxin solutions increases sugar accumulation and sink strength in developing auxin-induced parthenocarpic tomato fruits

The effects of the addition of gibberellic acid (GA) to auxin solutions for tomato fruit setting on sugar content and titratable acidity at maturity were investigated in ‘Louis 60’ tomatoes, and sucrolytic enzyme activities and cell development during the early stages of fruit development were examined to explain the physiological mechanisms. Days to maturity and titratable acidity were not affected by GA addition. The sugar concentration of the pericarp was increased by 50 mg L −1 of GA addition in the summer and the spring, but not in the autumn experiment. The product of sugar concentration and fruit weight, which is thought to reflect the amount of sugar per fruit, was higher in GA-treated fruit in every experiment. Beginning 1 day after treatment, cell size was larger in GA-treated fruit and resulted in an increase in pericarp thickness at maturity. These results suggest that GA addition at anthesis can promote an increased sink size of individual pericarp cells immediately after treatment. The activities of VAI and neutral invertase (NI) were higher in GA-treated fruit around 5 days after treatment, and the possibility of VAI and/or NI involvement in sink activity at an early stage of fruit development is suggested.

Responses of Yielding Ability, Sink Size and Percentage of Filled Grains to the Cultivation Practices in a Chinese Large-Panicle-Type Rice Cultivar, Yangdao 4

ReferencesA Chinese high-yielding large-panicle indica cultivar Yangdao 4 (YD) was examined for the response of yielding ability, sink size and percentage of filled grains (PFG), to the cultivation practice in comparison with a Japanese cultivar Hinohikari (HH) that had almost the same growth duration in 2005 and 2006. Treatments included planting density and number of seedlings hill-1, and supplement application of fertilizer to deep layer (SAFDL). Results revealed that the average sink size of YD was 17−28% larger than that of HH due to the larger number of spikelets panicle-1 and heavier grain weight. A significantly larger sink size was attained by the high density planting and SAFDL treatments in both cultivars, but not by changing the seedling number hill-1. The sink size of YD responded more significantly to the cultivation practices than that of HH. The average PFG in YD was about 10% higher than that in HH in both years. The PFG in both cultivars decreased with increasing sink size, but the decreasing rate in YD was 1/3 of that in HH and its yearly fluctuation was also less in YD than in HH. Consequently, the yield of YD increased with increasing sink size in contrast to HH. The average brown-rice yield of YD (640−653 g m-2) was 41−51% higher than that of HH (418−454 g m-2). In comparison with HH, the stable PFG in YD at increased sink size could be attributed to the increase of carbohydrate accumulation in the panicle (W+ T ), larger amount of NSC in the LS + C and higher NSC/sink size.

Effects of foliar application of BAP on source and sink strength in four six-rowed barley (Hordeum vulgare L.) cultivars

A field experiment was conducted to investigate the effects of foliar application of a synthetic cytokinin (BAP) on source and sink strength of four different six-rowed barley (Hordeum vulgare L.) cultivars. Different spraying treatments consisting of spraying on whole plant, spraying only on leaves and spraying only on ears started at anthesis and continued for 7 days. One additional spraying was carried out on late period of grain filling. Results showed that spraying only on leaves did not affect ear weight, grain yield and 1,000-grain weight, while the two other treatments increased all above mentioned traits. Neither of treatments affected stem weight, biological yield and contribution of stem reserves in grain filling. Exogenous cytokinin did not increase photosynthetic rate and chlorophyll content in treated leaves until late period of grain filling, although there was no significant increase in final grain weight due to late application of BAP. Our results suggested that effects of foliar application of BAP were mostly due to increased sink size soon after anthesis and increased sink demand probably met by current photosynthesis of organs other than leaves, like ear green tissues.

Increasing sink size does not increase photosynthesis during seed filling in soybean

Sink size at phloem-isolated nodes in soybean ( Glycine max L. Merrill) was increased to determine if a larger sink would stimulate photosynthesis. A larger sink was created by increasing the number of isolated nodes fed by a single leaf from one to three. Greenhouse grown plants (cultivar Elgin 87) were girdled below node 7 (one-node treatment) or below node 5 (three-node treatment) when the first flowers appeared at node 7. The stem above node 7 was removed at the time of girdling as were the leaves and petioles from nodes 5 and 6 on the three-node treatment. The three-node treatment produced approximately 40% more pods and seeds than the one-node treatment, but this increase in sink size had no effect on carbon exchange rate (CER) or leaf chlorophyll levels (estimated with a SPAD chlorophyll meter) during seed filling. There was no treatment effect on leaf soluble sugars, but starch levels tended to be slightly higher in the three-node treatment. These data provide no evidence that increasing the size of the sink exerts any affect on source activity. Mature weight per seed of the three-node treatment was reduced, but yield was the same as the one-node treatment. Our data are consistent with the concept that the seed sink is soybean is relatively passive and increasing sink size above its normal level does not exert a direct influence on leaf photosynthesis.

Quantitative Trait Loci for Sink Size and Ripening Traits in Rice (Oryza sativa L.).

Quantitative trait loci (QTLs) that affect sink size and ripening, which are often negatively correlated, were analyzed in two inbred lines of rice (Oryza sativa L.) derived from crosses between the semi-dwarf indica and japonica cultivars. Recombinant inbred lines (RILs) from Milyang23 (indica)/Akihikari (japonica), and back-crossed inbred lines (BCILs) from Sasanishiki (japonica)/Habataki(indica)//Sasanishiki///Sasanishiki were studied over a period of two years. A major QTL that was related to the number of spikelets per panicle was found in the same region of chromosome 1 in both populations. The indica allele increased the number of spikelets and reduced the ripening percentage. The indica allele of the QTL, which was found in both populations but at different locations on chromosome 6, also increased the number of spikelets per panicle, although to a lesser extent than in the case of the QTL on chromosome 1. In this instance, the number of spikelets per panicle did not have a negative effect on the ripening percentage. The increased number of spikelets produced by the QTL on chromosome 6 was due mainly to an increase in the number of primary rachis branches. In contrast, the effect of the QTL on chromosome 1 relied on an increase in the number of secondary rachis branches. In addition, dry matter production tended to increase when the QTL region of chromosome 6 belonged to the indica genotype. Therefore, both panicle structure and source productivity might contribute to the increase of the sink size without reducing the ripening percentage. We also found two loci on chromosomes 11 and 12 of the RILs that were associated with the percentage of incompletely filled spikelets, but which did not affect the sink size. It is considered that these QTLs could contribute significantly to the breeding of cultivars with increased sink size and increased ripening.

Efficiency of grain production of winter wheat as affected by N fertilisation under particular consideration of single culm sink size

Grain yield and yield components of winter wheat were recorded during 2-year field trials in Southern Bavaria, Germany. The impact of single ear sink size on the efficiency of grain production was studied in plants differing in single ear weight. While total grain yield showed only slight differences between N fertiliser treatments, significant variations were detected in harvest index and N harvest index. For single culms, a decrease in ear weight was related to decreasing values of harvest index and N harvest index. This correlation could not be altered by means of N fertilisation. The most efficient grain production, i.e. high value of harvest index and N harvest index, was regularly recorded in plant stands developing large single ear weights. The study confirms that with increasing sink size, the efficiency of grain production in winter wheat is improved. A N fertilisation strategy, favouring the formation of a large sink size, is described. In this respect, lower N rates in early spring and emphasis on N fertilisation during stem elongation proved to be decisive. This strategy favoured the generative growth at the expense of vegetative growth without excessively decreasing the corresponding source size.

Relationship of Enhanced Sink Demand with Photosynthesis and Amount and Activity of Ribulose 1,5-bisphosphate carboxylase in Soybean Leaves

Summary The presence of reproductive sinks is known to enhance the photosynthetic rate of soybean [ Glycine max (L.) Merr.] leaves. Thinning the plant stand at early podding to 25 % of normal plant density increased pod set and pod (plus seed) growth rate per plant, thereby increasing sink size of the remaining plants. CO 2 -exchange rate (CER), the contents of soluble protein and ribulose 1,5-bisphosphate carboxylase (Rubisco), as well as Rubisco activity, were determined for leaves of differing ontogeny. Leaf CER of plants with enhanced sink demand peaked at a higher level during the season, or the rates declined less rapidly during senescence than for control plants (normal density). CER was positively correlated with that of soluble protein and Rubisco content per unit leaf area. The percentage of protein that was Rubisco did not change in comparison with controls and, as the soluble protein increased after thinning, this led to an increased Rubisco activity per unit leaf area that was not due to increased Rubisco activity on a soluble protein basis. Thus, the greater sink demand increased CER or delayed its decline in soybean in parallel with the amount of Rubisco protein, not with the activity of the enzyme.