Sink limitation of wheat crops in the high rainfall zone of southern ...

Sink limitation of wheat crops in the high
rainfall zone of southern Australia
Heping Zhang, Neil C Turner and Mick Poole
CSIRO Plant Industry

Australian wheatbelt and the high rainfall zone
Wheat production
23 million tonnes per annum
Average yield:1.5-2 t/ha
Wheat belt
High rainfall zone
High rainfall zone (HRZ)
• Growing season >7-8 mths
• Rainfall: 550mm/year
• Total area 32Mha
• Arable area 2-6 Mha

The problem and hypothesis
• High yield potential (6-8 t/ha), but low
grain yield (50% of the potential)
achieved.
Wheat belt
High rainfall zone
• Lack of adapted cultivars – the cultivars
bred for the low and medium rainfall
zone wheatbelt are grown in the HRZ.
• Hypothesis: yield potential of wheat in
the HRZ is limited by sink size of the
current cultivars.

Methods and materials
• Sink-source balance experiment (2005-2007)
• A range of genotypes
• Measurement of sink size and source
• Sink size: the number of grains & kernel weight
• Source: Post-anthesis dry matter & WSC at
anthesis
• Comparison of balance of sink and source

Sink and source balance analysis
500
400
2005
(a) (b) (c)
2006
2007
WSC (g/m 2 )
300
200
100
0
Actual yield or potential source (g/m 2 )
800
600
400
200
0
2005
Calingiri Chara
Wyalk. HRZ216
(d)
2006
(e) 2007
(f)
Calingiri Chara Wyalk. HRZ216 Calingiri Chara Wyalk. HRZ203

Grain yield, grain number and kernel weight
700
50
600
45
Grain yield (g/m 2 )
500
400
300
200
100
Calingiri
Wyalkatchem
Kernel weight (mg)
40
35
30
25
0
4 6 8 10 12 14 16 18
20
4 6 8 10 12 14 16 18
Grain number (10 3 /m 2 )
Grain number (10 3 /m 2 )

Methods and materials
• Manipulation of sink and source to evaluate its
impact on yield and WSC
• 4 contrasting genotypes:
• 2 commercial cultivars (Calingiri & Wyalkatchem)
• 2 large sink size genotypes (Chara & HRZ203)
• Shading after anthesis
• Supplemental irrigation during grain filling

Shading experiment
Shading applied just after flowering
Reduce the incoming solar radiation by 40%

Shading - grain yield & DM

Shading – WSC left at maturity
60
50
l.s.d. (P < 0.05) = 15
No difference
WSC (g/m2)
40
30
20
10
0
Control
Shaded
Shading treatment

Irrigation during grain filling
33 mm water applied 10 days after anthesis

Irrigation – dry matter and grain yield

Irrigation – WSC left at maturity

Conclusion from the three experiments
• No yield reduction responses to shading of current cultivars
suggest that there were enough source (assimilates) to fill the
existing sink.
• No yield responses to irrigation but increases in WSC
remaining in the stem at maturity indicates that the sink size of
the current cultivars are not large enough to accommodate the
available assimilates.
• Sink size of the current cultivars are limited.
• The remaining question: do we have enough water to support a
large sink size crop?
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Is there enough water to support a large sink?
Year ETa (mm) ETpa
(mm)
ETa/ETpa
DMa
(t/ha)
Yield
(t/ha)
2001 255 126 2 10.8 5.5
2002 166 193 0.9 8.0 3.4
2003 184 219 0.9 11.8 5.9
Zhang et al. (2005) AJAR 56, 743-752

Water use pattern by six wheat cultivars
4
3
30/4/2005
ETa/ETpa
2
1
0
4
216 2185 W yalk calingiri Chara W ylah
3 0 /5 /2 0 0 5
3
ETa/ETpa
2
1
0
216 2185 W yalk calingiri Chara W ylah

Conclusion
• Current wheat cultivars grown in the HRZ are
more sink-limited than source limited.
• Increasing sink size of the current wheat cultivars
can provide opportunities to increase yield
potential of wheat in the HRZ.
• Our next step is to look at how to increase the
sink size and realise the water limited yield.

This work is funded by CSIRO and the Grains
Research and Development Corporation (GRDC) of
Australian Government.
CSIRO Plant Industry
Heping Zhang
Phone: 61 8 9333 6497
Email: heping.zhang@csiro.au
Web: www.csiro.au/cpi
Thank you