Ranking cereal varieties for frost susceptibility using frost values northern

¹ School of Agriculture, Food & Wine, The University of Adelaide
² Innovative Food Technologies, Agri-Science Queensland, Department of Agriculture and Fisheries
³ Statistics for the Australian Grains Industry (SAGI), Centre for Crop and Disease Management, Curtin University
⁴ Statistics for the Australian Grains Industry (SAGI), National Institute for Applied Statistics Research Australia (NIASRA), University of Wollongong
⁵ NSW Department of Primary Industries
⁶ Department of Agriculture and Food Western Australia

Take home message

• Wheat and barley varieties differ in susceptibility to reproductive frost damage during booting and flowering
• Barley is less susceptible to reproductive frost damage than wheat. No varieties are frost tolerant. Under severe frost (for example -8°C) or multiple minor frosts (several nights of -2° to -4°C) all varieties tested to date are equally susceptible, resulting in up to 100 percent sterility in flowering heads
• Variation in reproductive frost susceptibility has not been linked to variation in susceptibility to stem frosts experienced in 2014 across Southern Australia or to later frosts during grain filling
• Frost Values have been developed for cereal varieties to rank their relative susceptibility to reproductive frost. This information will be available through the use of an interactive tool on the National Variety Trial website and can be used to manage frost risk and fine tune variety selection after first selecting for local adaptation, yield, flowering time, and other key target traits.

Background

Frost has been estimated to cost Australian growers around $360 million in direct and indirect yield losses every year.  Breeding new cereal varieties with improved frost tolerance is one solution to minimise financial losses due to frost. Historically little has been known about variation for frost tolerance in Australian varieties, leading to the assumption that little variation exists. The limited knowledge about frost tolerance is also due to the practical difficulties in measuring frost damage under field conditions due to the sporadic and dynamic nature of frost events. However, successive GRDC funded projects have enabled dedicated frost screening nurseries to be developed in SA, WA and NSW. These nurseries have enabled the measurement of susceptibility to reproductive frost under minor frosts with greater accuracy and repeatability than previously. This research is part of the GRDC’s multidisciplinary National Frost Initiative.

Methodology

The frost susceptibility data is generated from research trials grown in frost prone parts of the commercial production environment near Loxton (SA), Merredin and Wickepin (WA), and Narrabri (NSW) in 2012, 2013 and 2014. To improve the predictions for these environments similar trials grown in Loxton (SA) in 2010 and 2011 were also included in the analysis.

At each site between 6 and 11 times of sowing (TOS) are planted as separate blocks at approximate equidistant thermal time from around April 15 to June 15 at each site to increase the probability that the test lines are at the flowering stage when a natural frost event occurs. On-site weather stations monitor the temperature at the crop canopy. Following a frost event, 30 flowering heads are tagged and then assessed for frost induced sterility (FIS) during grain fill 4-6 weeks later. FIS is assessed on the outside grains of every spikelet excluding the terminal and basal spikelets. This approach minimises confounding effects due to maturity and enables repeatable results over successive seasons and sites. Different research agencies conducted the trials in each state, although the same protocols were used. Table 1 gives a summary of the trials.

The genotypes that were grown included: a selection of the most commonly grown wheat and barley varieties in the three states; genotypes which had been well characterised previously for frost tolerance; and other genotypes of particular interest to breeding companies.

Table 1. Summary of wheat experiments used in analysis, replications =2.

Results and discussion

When cereal varieties are flowering on the same day and a frost occurs, there is a wide range in frost susceptibility within commercial varieties under mild reproductive frost conditions (minimum temperature -1° to -3°C) (Figure 1). Under very severe frost (for example -8°C) or multiple minor frosts (several nights of -2° to -4°C) all varieties are equally susceptible, resulting in up to 100 per cent sterility. It should be noted that the relationship between canopy temperature and FIS is complex and can be confounded by TOS, variety and environmental factors. Understanding this relationship will be the focus of ongoing research. 

Frost values

The relative ranking of the frost susceptibility has been expressed as a frost value (FV) for each variety in each environment. FVs are presented as positive or negative differences relative to the average frost induced sterility (FIS) of all varieties in the current data-set for a given year and site. Low FVs are more desirable than high FVs. The units of measurement for FVs relate to the transformed FIS data and therefore do not directly correspond to a particular level of frost damage. Therefore, the comparative ranking between a subset of varieties of interest should be considered when making variety decisions as it is the difference between FVs that is critical.

When using FVs for selection decisions, it is recommended that growers and advisors consider not just a single environment/year, but a number of relevant environments. This allows examination of stability of variety performance over a range of environments which are prone to frosts.

FVs can be displayed graphically for a set of either wheat or barley varieties of interest using the interactive tool that is available from NVT Online.  An example of this is shown in Figure 2.  

The rankings are currently based on the variation in wheat and barley varieties' ability to maintain grain number under minor reproductive frosts. Under reproductive/floret or head frosts grain number is the main yield component affected. Yield is a function of grain size multiplied by grain number and hence grain number normally corresponds to yield. However, this may not be the case if there is variation in the length of season and the ability of varieties to compensate with late tillers, synchronisation of flowering time, or plasticity of grain number. Therefore, it is critical that varieties are selected on local adaptation and yield first and FVs are only used to identify and manage frost risk.

Further research is ongoing to validate the yield relationship with FIS (DAW00234) and also compensation ability (CSP00180) as part of the GRDC’s multidisciplinary National Frost Initiative.

In addition it is important to note that research to date has not conclusively assessed if the variation in reproductive frost susceptibility is related to susceptibility to frost during stem elongation and grain filling.

Figure 1. Relationship between minimum temperature in 3 environments and raw FIS data for each wheat tagging event, at different development stages in 2012-2013.

Figure 2. Frost Value graph for five wheat varieties tested at Narrabri NSW. Each FV for each variety is presented along with prediction standard error bars. The number of tagging events is indicated in brackets for each site/year. Lower FVs are better.
(​EGA Gregory, Spitfire, Suntop & Corack are all varieties protected under the Plant Breeders Rights Act 1994)

Conclusion

As frost exerts a complex production constraint in cropping systems, it requires a package of risk management strategies. These strategies should include pre-season, in-crop and post-frost management tactics. These tactics should be regularly reviewed and updated as part of annual farm management planning and as new ideas and research findings are uncovered.

Variation in cereal varieties for reproductive frost susceptibility is just one component of a management strategy and may be used to fine-tune variety selection to manage the risk of frost damage.

Acknowledgements

The authors acknowledge Mr Nathan Height and Mike Baker DAFWA for technical support. Trials in Narrabri were sown and managed by Kalyx and by Living Farm in Wickepin. This research was funded by the GRDC and is part of the National Frost Initiative. 

Contact details

Richard Maccallum
NSW Department of Primary Industries
Ph: 02 6895 1025
Email: richard.maccallum@dpi.nsw.gov.au

Tim March
University of Adelaide
Ph: 08 8313 6700
Email: tim.march@adelaide.edu.au

Jason Eglinton
University of Adelaide
Ph: 08 8303 6553
Email: jason.eglinton@adelaide.edu.au

Ben Biddulph
DAFWA, South Perth
Ph: 08 9368 3431
Email: ben.biddulph@agric.wa.gov.au

​Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994