1. Breeding cotton for a variable rainfall environment
18th Australian Cotton Conference, Broadbeach, QLD
Warren Conaty, David Johnston, Alan Thompson, Susan Jaconis, and Greg Constable
August 11th 2016
CSIRO agriculture AND FOOD

2. CSIRO rainfed breeding program
Parental Selection
F2& F3 Evaluations
F4 Single Plant Selection
Initial Evaluations
(Narrabri)
Progeny Rows
Intermediate
Preliminary Offsite
Preliminary Onsite
Advanced Material
onsite location
(Narrabri)
Up to 5 offsite locations
Managed water stress to improve rainfed breeding | Warren Conaty

3. Australian rainfall patterns
Highly variable rainfall
Summer dominant
Average 650mm
In-crop 350mm
Skewed
Figure 1. (a) Frequency of in-crop rainfall and (b) variability in monthly in-crop rainfall for Narrabri.
Managed water stress to improve rainfed breeding | Warren Conaty

4. The problem
One-in-five years has low yield (<550 kg ha-1) and has no statistical difference between genotypes i.e. we cannot reliably select superior lines.
Historically, to manage the risk of rainfall variability the CSIRO rainfed breeding program has:
selected for indeterminate cultivars;
utilised skip-row configurations;
reduced nitrogen inputs, and;
pre-irrigated rainfed evaluations to simulate a full soil water profile.
However:
One-in-five years has low yield (<550 kg ha-1) and has no statistical difference between genotypes - i.e. we cannot reliably select superior lines.
Managed water stress to improve rainfed breeding | Warren Conaty

5. Hypothesis
Application of a single furrow irrigation in dry years will increase trial yields above the threshold of statistical genotypic resolution
Managed water stress to improve rainfed breeding | Warren Conaty

6. Aims
To determine if and when a single irrigation could be applied to rainfed evaluations when yield is expected to fall below the confidence threshold
(Crop Modeling)
To assess the stability of germplasm performance under both rainfed conditions and limited water situations
(Field Trials)
clarify if germplasm selected under rainfed conditions can produce high lint yields in seasons with higher than average rainfall.
Managed water stress to improve rainfed breeding | Warren Conaty

7. Development of: Managed stress system (MSS)
Result: An irrigation should be applied to a ‘rainfed’ experiment when soil water deficit reached mm by DAS
Managed water stress to improve rainfed breeding | Warren Conaty

8. Field Validation: MSS Three seasons
Figure 4. Soil water deficit for each season in Rainfed and MSS treatment
Three seasons
21 genotypes grown under rainfed and managed stress
Soil water deficit measured via neutron attenuation
Yield analysis
Managed water stress to improve rainfed breeding | Warren Conaty

9. MSS Validation- Results
Rainfed
Sowing year
Treatment
Rainfall
(mm)
Avg. trial yield
(kg ha-1)
Genotype
p-value
Co-efficient of variation
(%)
Treatment x genotype
2013
Rainfed
127
546
0.329
16.4
0.726
MSS
1121
0.008
9.9
2014
199
785
0.002
11.0
0.020
1324
0.004
7.8
2015
350
823
<0.001
14.1
n/a
Managed water stress to improve rainfed breeding | Warren Conaty

10. Interactions
Genotype rankings differed significantly between rainfed and MSS in 2014/2015.
different rainfall and crop fruit setting pattern.
driven by low and medium yielding genotypes
high yielding genotypes are consistent
interaction is no longer significant when looking at multiple years
Genotype rankings under MSS were different to rainfed in 2014/15.
Due to effect of different rainfall pattern on genotypes with different crop setting pattern.
Genotype rankings differed significantly between rainfed and MSS.
This interaction was driven by low and medium yielding genotypes. Thus selection for yield under MSS would not necessarily omit the best yielders from rainfed in dry seasons. More seasons of testing are required to evaluate this interaction.
Figure 5. Rainfed and MSS rankings for lint yields (2013/2014 and 2014/2015).
Managed water stress to improve rainfed breeding | Warren Conaty

11. Main Conclusions
Developed a managed stress system that optimized a single irrigation to meet yield threshold
Irrigating the MSS was necessary to resolve genotype differences in 2013/14
When rainfed yields increase due to rainfall, the MSS was not necessary to resolve genotype differences
MSS
Rainfed
Managed water stress to improve rainfed breeding | Warren Conaty

12. What does this mean for our breeding program?
Using the MSS, we are able to get useful data in years when yields would be too low to evaluate genotypes
Since grower income is greater under better environments than very limited water situations, genotype performance under MSS may actually identify better and more realistic long term options for growers.
Best performing genotypes under rainfed conditions in dry seasons will also be captured. Rainfed genotype evaluation is repeated over multiple seasons and sites and genotype selection is based on all sites, not just MSS.
Rainfed genotype evaluation is repeated over multiple seasons and sites and genotype selection is based on all sites, not just MSS. Thus best performers under rainfed conditions in dry seasons will not be missed.
Note however that since grower income is greater under better environments than very limited water situations, genotype performance under MSS may actually identify better long term options for growers.
Managed water stress to improve rainfed breeding | Warren Conaty

13. CSIRO rainfed breeding program
Parental Selection
F2& F3 Evaluations
F4 Single Plant Selection
Initial Evaluations
(Narrabri)
Progeny Rows
Intermediate
Preliminary Offsite
Preliminary Onsite
Advanced Material
MSS
onsite location
(Narrabri)
5 offsite locations
Managed water stress to improve rainfed breeding | Warren Conaty

14. Thank you
Thank you to the technical staff of CSIRO cotton breeding group, particularly Mark Laird, Mick Price, Adam Suckling, Megan Cameron, Deon Cameron, Jo Price and Kellie Cooper for their invaluable contribution to this work.
CSIRO cotton breeding is undertaken in the Cotton Breeding Australia joint venture between CSIRO and Cotton Seed Distributors.
CSRIO AGRICULTURE AND FOOD
Dr Warren Conaty
Research Scientist
CSIRO AGRICULTURE AND FOOD