Source - sink balance and manipulating sink - source relations of wheat indicate that the yield potential of wheat is sink-limited in high-rainfall zones

Grain yield depends on the number of grains per unit area (sink) and the availability of assimilates (source) to fill these grains. The aim of the current work was to determine whether wheat yield in the high-rainfall zone of south-western Australia is limited in current cultivars by the size of the sink or by the assimilates available for grain filling. Three wheat cultivars (Calingiri, Chara and Wyalkatchem) and two breeding lines (HRZ216 and HRZ203) were grown in four replicates in the field from 2005 to 2007. Dry matter and water soluble carbohydrates (WSC) at anthesis and maturity were measured and used to determine the source and sink balance of the crop. In 2007, three further treatments were applied to manipulate the sink–source relationships: (i) spikelets were removed on main stems to increase the source : sink ratio; (ii) incoming solar radiation was reduced by 40% by shading after anthesis to reduce the availability of assimilates to grains; and (iii) supplemental irrigation was used to maintain the capacity for photosynthesis by an improved water supply during grain filling. The source–sink balance of the crops showed that the potential source was 25% greater than the actual grain yield in average and above-average seasons (2005 and 2007), suggesting that sink size, represented by the number of grain per unit area, was a limiting factor to yield potential. However, the source may have become a limiting factor in a drought season (2006). The grain yield increased with increased number of grains/m2 and kernel weight remained relatively stable even when grain number increased from 7000 to 16 000 per m2. The removal of half of the spikelets on the main stem did not increase kernel mass of the remaining grains and an additional 33 mm of irrigation water did not increase grain yield, but significantly (P < 0.05) increased WSC left in stems and leaf sheaths at maturity. Shading after anthesis did not significantly reduce grain yield of the current cultivars Calingiri and Wyalkatchem, but it reduced grain yield by 23–25% (P < 0.05) in Chara and HRZ203. The source–sink balance over three seasons and three independent experiments in 2007 suggested that the yield of the current wheat cultivars is more sink- than source-limited and that breeding wheat with a larger sink size than in the current cultivars may lift the yield potential of wheat in the high-rainfall zone of south-western Australia.

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Estimating Organ Contribution to Grain Filling and Potential for Source Upregulation in Wheat Cultivars with a Contrasting Source–Sink Balance

Agronomy ◽

10.3390/agronomy10101527 ◽

2020 ◽

Vol 10 (10) ◽

pp. 1527

Author(s):

Carolina Rivera-Amado ◽

Gemma Molero ◽

Eliseo Trujillo-Negrellos ◽

Matthew Reynolds ◽

John Foulkes

Keyword(s):

Grain Growth ◽

Photosynthetic Rate ◽

Grain Filling ◽

Leaf Sheath ◽

Grain Weight ◽

Yield Potential ◽

Wheat Cultivars ◽

Sink Limitation ◽

Source Sink ◽

Source And Sink

Grain filling may be limited by the joint source and sink capacity in modern wheat cultivars, indicating a need to research the co-limitation of yield by both photosynthesis and the number and potential size of grains. The extent to which the post-anthesis source may be limiting final grain size can be estimated by partial degraining of spikes, while defoliation and shading treatments can be useful to estimate if any excess photosynthetic capacity exists. In the current study, degraining was applied to a set of 26 elite spring wheat cultivars from the International Maize and Wheat Improvement Center (CIMMYT)’s core germplasm (CIMCOG) panel, while lamina defoliation and shading through stem-and-leaf-sheath covering treatments were applied to a subset of the same cultivars. Responses to source treatments in grain weight, pre-anthesis reserve contribution to grain weight, dry-matter translocation efficiency, and flag-leaf and spike photosynthetic rate were measured and compared to an unmanipulated control treatment. Grain weight responses to degraining among cultivars ranged from no response to increases of 28%, suggesting a range of responses from sink limitation, to probable source and sink co-limitation of grain growth. Grain weight’s response to degraining increased linearly with the years of cultivar release from 1966 to 2009, indicating that the current highest yield potential CIMMYT spring wheats have a co-limitation of grain growth by source and sink. This may have been due to an increase in grain sink strength with years of cultivar release with no commensurate increase in post-anthesis source capacity. The relatively low decreases in grain weight with defoliation compared to decreases in light interception by defoliation indicated that sink limitation was still likely predominating in the cultivars with co-limitation. The stem-and-leaf-sheath covering treatment decreased grain weight by nearly 10%, indicating that stem-and-leafsheath photosynthesis plays a key role in grain growth during grain filling. In addition, pre-anthesis reserve contribution to grain weight was increased by ca. 50% in response to lamina defoliation. Our results showed that increasing the post-anthesis source capacity, through increases in stem-and-leaf-sheath photosynthetic rate during grain filling and pre-anthesis reserve contribution to grain weight, is an important objective in enhancing yield potential in wheat through maintaining a source–sink balance.

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Grain weight in wheat cultivars released from 1920 to 1990 as affected by post-anthesis defoliation

The Journal of Agricultural Science ◽

10.1017/s0021859696004133 ◽

1997 ◽

Vol 128 (3) ◽

pp. 273-281 ◽

Cited By ~ 48

Author(s):

B. C. KRUK ◽

D. F. CALDERINI ◽

G. A. SLAFER

Keyword(s):

Grain Yield ◽

Plant Breeding ◽

Field Experiments ◽

Wheat Breeding ◽

Grain Weight ◽

Yield Potential ◽

Sink Strength ◽

Wheat Cultivars ◽

The Difference ◽

Source Sink

Although it has been generally recognized that the difference in yield potential amongst wheat cultivars released in different eras is related to differences in their reproductive sink strength, there have been few investigations about changes in source–sink ratios as a consequence of wheat breeding. In the present study, two field experiments, in which plots were fertilized and irrigated and lodging and diseases were prevented, were carried out with seven cultivars (including a commercial hybrid) representing different periods of plant breeding in Argentina from 1920 to 1990. The cultivars were defoliated during post-anthesis to analyse the response of grain weight at particular positions within the spike (which have intrinsic differences in potential size).Individual grain weight was virtually unaffected by defoliation in the old cultivars, but modern cultivars exhibited a significant reduction in individual grain weight for several positions within the spike, although this reduction was small (c. 15%) and many grains were unaffected. In addition, no relationship was found between individual grain weight in the controls and its reduction due to defoliation.We concluded that if the source–sink ratio is further reduced, the grain yield of modern wheats will be simultaneously limited by the source and the sink. Future breeding should therefore attempt to improve simultaneously both sink and source strengths.

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Contribution of Stem Dry Matter to Grain Yield in Wheat Cultivars

Functional Plant Biology ◽

10.1071/pp9910053 ◽

1991 ◽

Vol 18 (1) ◽

pp. 53 ◽

Cited By ~ 51

Author(s):

PC Pheloung ◽

KHM Siddique

Keyword(s):

Water Stress ◽

Grain Yield ◽

Dry Matter ◽

Field Experiments ◽

Yield Potential ◽

Percentage Reduction ◽

Wheat Cultivars ◽

Activity Increase ◽

Structural Carbohydrate ◽

Days After Anthesis

Field experiments were conducted in the eastern wheat belt of Western Australia in a dry year with and without irrigation (1987) and in a wet year (1988), comparing three cultivars of wheat differing in height and yield potential. The aim of the study was to determine the contribution of remobilisable stem dry matter to grain dry matter under different water regimes in old and modern wheats. Stem non-structural carbohydrate was labelled with 14C 1 day after anthesis and the activity and weight of this pool and the grain was measured at 2, 18 and 58 days after anthesis. Gutha and Kulin, modern tall and semi-dwarf cultivars respectively, yielded higher than Gamenya, a tall older cultivar in all conditions, but the percentage reduction in yield under water stress was greater for the modern cultivars (41, 34 and 23%). In the grain of Gamenya, the increase in 14C activity after the initial labelling was highest under water stress. Generally, loss of 14C activity from the non-structural stem dry matter was less than the increase in grain activity under water stress but similar to or greater than grain activity increase under well watered conditions. Averaged over environments and cultivars, non-structural dry matter stored in the stem contributed at least 20% of the grain dry matter.

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Variation in harvest index of modern spring barley, oat and wheat cultivars adapted to northern growing conditions

The Journal of Agricultural Science ◽

10.1017/s0021859607007368 ◽

2007 ◽

Vol 146 (1) ◽

pp. 35-47 ◽

Cited By ~ 39

Author(s):

P. PELTONEN-SAINIO ◽

S. MUURINEN ◽

A. RAJALA ◽

L. JAUHIAINEN

Keyword(s):

Grain Yield ◽

Harvest Index ◽

Stand Structure ◽

Spring Barley ◽

Principal Component ◽

Grain Filling ◽

Wheat Cultivars ◽

Cereal Species ◽

Growing Conditions ◽

Cereal Cultivars

SUMMARYIncreased harvest index (HI) has been one of the principal factors contributing to genetic yield improvements in spring barley (Hordeum vulgare L.), oat (Avena sativa L.) and wheat (Triticum aestivum L.) cultivars. Although high HI demonstrates high-yielding ability when cultivars are compared, it can also indicate challenges to yield formation when comparisons are made across differing growing conditions. The present study was designed to investigate variation in HI among modern cereal cultivars relative to that brought about by a northern environment, to assess whether HI still explains the majority of the differences in grain yield when only modern cereal cultivars are compared, and to monitor key traits contributing to HI. Stability of HI was also investigated with reference to the role of tillers. Twelve experiments (3 years, two locations, two nitrogen fertilizer regimes) were carried out in southern Finland to evaluate 12 two-row spring barley, 10 six-row barley, 10 oat and 11 wheat cultivars. In addition to HI, days to heading and maturity, length of grain filling period, grain yield, test weight and 13 traits characterizing plant stand structure were measured and analysed with principal component analysis (PCA) to detect traits associated with HI and those contributing to stability of HI. Although only modern cereals were studied, differences among cultivars were significant both in mean HI and stability of HI, and HI was associated with short plant stature in all modern cereal species. Also, single grain weight was associated with HI in all species. Differences between, but not within, species in HI were partly attributable to differences in tiller performance. Grain yield was associated closely with HI except in two-row barley. It may be possible to further increase HI of wheat, as it still was relatively low. High HI did, however, not indicate the degree of success in yield determination when environments are compared.

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Optimising grain yield and grazing potential of crops across Australia’s high-rainfall zone: a simulation analysis. 2. Canola

Crop and Pasture Science ◽

10.1071/cp14240 ◽

2015 ◽

Vol 66 (4) ◽

pp. 349 ◽

Cited By ~ 33

Author(s):

Julianne M. Lilley ◽

Lindsay W. Bell ◽

John A. Kirkegaard

Keyword(s):

Grain Yield ◽

New South ◽

New South Wales ◽

Yield Potential ◽

N Availability ◽

Dual Purpose ◽

High Rainfall ◽

South Wales ◽

Vernalisation Requirement ◽

Crop Density

Recent expansion of cropping into Australia’s high-rainfall zone (HRZ) has involved dual-purpose crops suited to long growing seasons that produce both forage and grain. Early adoption of dual-purpose cropping involved cereals; however, dual-purpose canola (Brassica napus) can provide grazing and grain and a break crop for cereals and grass-based pastures. Grain yield and grazing potential of canola (up until bud-visible stage) were simulated, using APSIM, for four canola cultivars at 13 locations across Australia’s HRZ over 50 years. The influence of sowing date (2-weekly sowing dates from early March to late June), nitrogen (N) availability at sowing (50, 150 and 250 kg N/ha), and crop density (20, 40, 60, 80 plants/m2) on forage and grain production was explored in a factorial combination with the four canola cultivars. The cultivars represented winter, winter × spring intermediate, slow spring, and fast spring cultivars, which differed in response to vernalisation and photoperiod. Overall, there was significant potential for dual-purpose use of winter and winter × spring cultivars in all regions across Australia’s HRZ. Mean simulated potential yields exceeded 4.0 t/ha at most locations, with highest mean simulated grain yields (4.5–5.0 t/ha) in southern Victoria and lower yields (3.3–4.0 t/ha) in central and northern New South Wales. Winter cultivars sown early (March–mid-April) provided most forage (>2000 dry sheep equivalent (DSE) grazing days/ha) at most locations because of the extended vegetative stage linked to the high vernalisation requirement. At locations with Mediterranean climates, the low frequency (<30% of years) of early sowing opportunities before mid-April limited the utility of winter cultivars. Winter × spring cultivars (not yet commercially available), which have an intermediate phenology, had a longer, more reliable sowing window, high grazing potential (up to 1800 DSE-days/ha) and high grain-yield potential. Spring cultivars provided less, but had commercially useful grazing opportunities (300–700 DSE-days/ha) and similar yields to early-sown cultivars. Significant unrealised potential for dual-purpose canola crops of winter × spring and slow spring cultivars was suggested in the south-west of Western Australia, on the Northern Tablelands and Slopes of New South Wales and in southern Queensland. The simulations emphasised the importance of early sowing, adequate N supply and sowing density to maximise grazing potential from dual-purpose crops.

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Sucrose transport and metabolism control carbon partitioning between stem and grain in rice

Journal of Experimental Botany ◽

10.1093/jxb/erab066 ◽

2021 ◽

Author(s):

Jyotirmaya Mathan ◽

Anuradha Singh ◽

Aashish Ranjan

Keyword(s):

Grain Yield ◽

Wild Rice ◽

Grain Filling ◽

Invertase Activity ◽

Cultivated Rice ◽

Sucrose Transport ◽

Unit Leaf ◽

In The Wild ◽

Source Sink ◽

Oryza Australiensis

Abstract The source-sink relationship is key to overall crop performance. Detailed understanding of the factors that determine source-sink dynamics is imperative for the balance of biomass and grain yield in crop plants. We investigated the differences in the source-sink relationship between a cultivated rice Oryza sativa cv. Nipponbare and a wild rice Oryza australiensis that show striking differences in biomass and grain yield. Oryza australiensis, accumulating higher biomass, not only showed higher photosynthesis per unit leaf area but also exported more sucrose from leaves than Nipponbare. However, grain features and sugar levels suggested limited sucrose mobilization to the grains in the wild rice due to vasculature and sucrose transporter functions. Low cell wall invertase activity and high sucrose synthase cleavage activity followed by higher expression of cellulose synthase genes in Oryza australiensis stem utilized photosynthates preferentially for the synthesis of structural carbohydrates, resulting in high biomass. In contrast, the source-sink relationship favored high grain yield in Nipponbare via accumulation of transitory starch in the stem, due to higher expression of starch biosynthetic genes, which is mobilized to panicles at the grain filling stage. Thus, vascular features, sucrose transport, and functions of sugar metabolic enzymes explained the differences in the source-sink relationship between Nipponbare and Oryza australiensis.

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Plant population and shading studies in barley

The Journal of Agricultural Science ◽

10.1017/s0021859600064510 ◽

1971 ◽

Vol 77 (3) ◽

pp. 445-452 ◽

Cited By ~ 36

Author(s):

R. W. Willey ◽

R. Holliday

Keyword(s):

Grain Yield ◽

Dry Matter ◽

Unit Area ◽

Grain Filling ◽

Crop Growth ◽

Plant Population ◽

Grain Number ◽

Ear Development ◽

Development Period ◽

Lower Production

SUMMARYTwo barley experiments are described in which a range of plant populations were shaded during different periods of development. Shading during the ear development period caused considerable reductions in grain yield, largely by reducing the number of grains per ear. Shading during the grain-filling period caused no reduction in grain yield. It is suggested that under conditions of these experiments there was probably a potential surplus of carbohydrate available for grain filling and that grain yield was largely determined by the storage capacity of the ears. The importance of the number of grains per ear as an indicator of individual ear capacity is emphasized.The effects of plant population on grain yield and its components are also examined. It is concluded that the number of grains per ear is the component having greatest influence on the decrease in grain yield at above-optimum populations and attention is again drawn to the possible importance of ear capacity. It is argued that on an area basis the number of grains per unit area may give a good indication of ear capacity. Examination of this parameter shows a close relationship with grain yield per unit area for both the shading and population treatments. It is particularly evident that a decrease in grain yield at high populations was associated with a comparable decrease in the number of grains per unit area. It is suggested that this decrease in grain number may be due to a lower production of total dry matter during ear development rather than an unfavourable partitioning of this dry matter between the ear and the rest of the plant. This lower production of total dry matter is attributed to the crop growth rates of the higher populations having reached their peak and then having declined before the end of the ear development period. This crop growth rate pattern, through its effect on grain number per unit area, is put forward as the basic reason why, in the final crop, grain yield per unit area decreases at above-optimum populations.

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Grain yield increases in wheat and barley to nitrogen applied after transient waterlogging in the high rainfall cropping zone of western Australia

Journal of Plant Nutrition ◽

10.1080/01904167.2014.993475 ◽

2015 ◽

Vol 39 (7) ◽

pp. 974-992 ◽

Cited By ~ 8

Author(s):

Narelle L. Simpson ◽

Ross F. Brennan ◽

Walter K. Anderson

Keyword(s):

Grain Yield ◽

Western Australia ◽

High Rainfall

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Grain nitrogen concentration differences among three sorghum hybrids with similar grain yield

Australian Journal of Agricultural Research ◽

10.1071/a98029 ◽

1999 ◽

Vol 50 (2) ◽

pp. 137 ◽

Cited By ~ 4

Author(s):

A. Kamoshita ◽

M. Cooper ◽

R. C. Muchow ◽

S. Fukai

Keyword(s):

Grain Yield ◽

Nitrogen Concentration ◽

N Uptake ◽

Grain Filling ◽

Yield Potential ◽

Yield Reduction ◽

N Availability ◽

N Accumulation ◽

N Concentration ◽

Grain Nitrogen

The differences in grain nitrogen (N) concentration among 3 sorghum (Sorghum bicolor (L.) Moench) hybrids with similar grain yield were examined under N-limiting conditions in relation to the availability of assimilate and N to grain. Several manipulation treatments [N fertiliser application, lower leaves shading, thinning (reduced plant population), whole canopy shading, canopy opening, spikelet removal] were imposed to alter the relative N and assimilate availability to grain under full irrigation supply. Grain N concentration increased by either increased grain N availability or yield reduction while maintaining N uptake. Grain N concentration, however, did not decrease in the treatments where relative abundance of N compared with assimilate was intended to be reduced. The minimum levels of grain N concentration differed from 0.95% (ATx623/RTx430) to 1.14% (DK55plus) in these treatments. Regardless of the extent of variation in assimilate and N supply to grain, the ranking of hybrids on grain N concentration was consistent across the manipulation treatments. For the 3 hybrids examined, higher grain N concentration was associated with higher N uptake during grain filling and, to a lesser extent, with higher N mobilisation. Hybrids with larger grain N accumulation had a larger number of grains. There was no tradeoff between grain N concentration and yield, suggesting that grain protein concentration can be improved without sacrificing yield potential.

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