Abstract
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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Claims 11
Claim · model-written summary
Potential source exceeded actual grain yield by 25% in average and above-average seasons.
- Outcome
- potential sourcee0
- Direction
- greatere0
- Value
- 25%e0
- Qualifier
- average and above-average seasons (2005 and 2007)e0
- Comparator
- actual grain yielde0
Not reportedTaxon
Verbatim
e0“potential source was 25% greater than the actual grain yield in average and above-average seasons (2005 and 2007)”
Claim · model-written summary
Source may have limited yield in the drought season.
Not reportedTaxon
Verbatim
e0“source may have become a limiting factor in a drought season (2006)”
Claim · model-written summary
Grain yield rose with grain number per square meter.
Not reportedTaxon
Verbatim
e0“grain yield increased with increased number of grains/m2”
Claim · model-written summary
Kernel weight remained stable as grain number increased from 7000 to 16 000 per square meter.
- Outcome
- kernel weighte0
- Direction
- remained relatively stablee0
- Qualifier
- 7000 to 16 000 per m2e0
- Comparator
- grain numbere0
Not reportedTaxon
Verbatim
e0“kernel weight remained relatively stable even when grain number increased from 7000 to 16 000 per m2”
Claim · model-written summary
Removing half the main-stem spikelets did not increase remaining-grain kernel mass.
- Treatment
- removal of half of the spikelets on the main steme0
- Outcome
- kernel mass of the remaining grainse0
- Direction
- did not increasee0
Not reportedTaxonComparator
Verbatim
e0“removal of half of the spikelets on the main stem did not increase kernel mass of the remaining grains”
Claim · model-written summary
An additional 33 mm of irrigation did not increase grain yield.
Not reportedTaxonComparator
Verbatim
e0“additional 33 mm of irrigation water did not increase grain yield”
Claim · model-written summary
Additional irrigation significantly increased carbohydrates remaining in stems and leaf sheaths.
- Treatment
- additional 33 mm of irrigation watere0
- Outcome
- WSC left in stems and leaf sheaths at maturitye0
- Direction
- increasede0
Not reportedTaxonComparator
Verbatim
e0“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”
Claim · model-written summary
Post-anthesis shade did not significantly reduce grain yield in Calingiri and Wyalkatchem.
- Material
- Calingiri and Wyalkatcheme0
- Treatment
- Shading after anthesise0
- Outcome
- grain yielde0
- Direction
- did not significantly reducee0
Not reportedTaxonComparator
Verbatim
e0“Shading after anthesis did not significantly reduce grain yield of the current cultivars Calingiri and Wyalkatchem”
Claim · model-written summary
Post-anthesis shade reduced Chara and HRZ203 grain yield by 23–25%.
Not reportedTaxonTreatmentComparator
Verbatim
e0“reduced grain yield by 23–25% (P < 0.05) in Chara and HRZ203”
Claim · model-written summary
The authors infer current wheat cultivars are more sink than source limited.
- Taxon
- wheat
Triticum aestivume0 - Outcome
- yielde0
- Qualifier
- more sink- than source-limitede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“yield of the current wheat cultivars is more sink- than source-limited”
Claim · model-written summary
The authors suggest breeding wheat for larger sink size to lift yield potential.
- Taxon
- wheatTriticum aestivume0
- Treatment
- breeding wheat with a larger sink sizee0
- Outcome
- yield potentiale0
- Direction
- lifte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“breeding wheat with a larger sink size than in the current cultivars may lift the yield potential of wheat”
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