Grains Research and Development

Date: 10.02.2015

Preliminary rating of wheat varieties for susceptibility to reproductive frost damage

Author: Ben Biddulph, Michael Laws, Paul Eckermann, Richard Maccallam, Brenton Leske, Tim March, Jason Eglinton

Ben Biddulph3, Michael Laws1, Paul Eckermann1, Richard Maccallam2, Brenton Leske2, Tim March1, Jason Eglinton1.

1The University of Adelaide, 2NSW Department of Primary Industries, 3Department of Agriculture and Food Western Australia.

GRDC project codes: UA00136, DAW00234, CSP00143, DAW00162, UA00114, UA00063, UA00100.

Keywords: Frost, wheat, grain sterility, frost induced sterility, flowering.

Take home messages

  • Wheat varieties differ in susceptibility to reproductive frost damage during booting and flowering;
  • The preliminary rating of wheat varieties for susceptibility to reproductive frost will be available on the National Variety Trial website, www.nvtonline.com.au. Ratings should be used to manage the frost risk of new varieties after they are adopted, based on how known varieties of similar rating are currently managed;
  • Variation in reproductive frost susceptibility has not been linked to variation in susceptibility to the stem frosts experienced in 2014 across southern Australia, or to later frosts during grain filling.
  • No wheat varieties are frost tolerant. Under severe frost, for example -8°C or multiple minor frosts such as several nights of -2o to -4oC, all varieties tested to date are equally susceptible, resulting in up to 100 per cent sterility in flowering heads.

Background

Frost has been estimated to cost Australian growers around $360 million in direct and indirect yield losses every year.

Breeding new varieties with improved frost tolerance is the ultimate solution to minimise economic losses due to frost. Historically little has been know 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 because of 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 to measure susceptibility to reproductive frost under minor frosts with greater accuracy and repeatability.

Reproductive frost damage measured by frost induced sterility (FIS) is defined as intermittent or partial floret sterility. The sterility is often the combined effect of cold and freezing damage to the floral organs, primarily the anthers before and at flowering (Z45-65). This is also referred to as floret, flowering or head frost damage.

Methodology

The frost susceptibility data is generated from research trials grown in 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 included in the analysis.

At each site, between six and 11 times of sowing (TOS) were planted as separate blocks at approximately equidistant thermal time from around April 15th to June 15th to increase the probability that the test lines were at the flowering stage when a natural frost event occurred. On site weather stations monitor the temperature at the crop canopy. Following a frost event, 30 flowering heads were tagged and assessed for FIS of the outside grains during grain fill four to six weeks later. This approach minimises confounding effects due to maturity and enables repeatable results over successive seasons and sites. Different groups conducted the trials in each state, although the same protocols were used. Table 1 summarises each trial.

The genotypes grown included a selection of the most commonly grown wheat 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.

State

Location

Year

Number of sowing dates

Number of varieties

SA

Loxton

2010

6

35

2011

6

36

2012

11

65

2013

10

65

2013

10

72

WA

Merredin

2012

7

48

Wickepin

2013

6

54

2014

8

72

NSW

Narrabri

2012

7

30

2013

7

32

2013

7

32

Results and discussion

When commercial wheat varieties are flowering on the same day, and a frost occurs, there is a wide range in reproductive frost susceptibility, measure by FIS, under mild reproductive frost conditions, such as minimum temperature -1o to -3oC (Figure 1 and 2). Under very severe frost, for example -8°C, or multiple minor frosts, several nights of -2o to -4oC, all varieties are equally susceptible resulting in 100 per cent FIS. Ratings of relative frost susceptibility of commercial wheat and barley varieties were not available at time of paper preparation but will be presented and made available prior to seeding in 2015 through the National Variety Testing website, www.nvtonline.com.au.

How will a variety be rated and how do I use it?

A particular variety will be given a preliminary rating as very susceptible or moderately susceptible to reproductive frost damage. The ratings are not due to difference in phenology or flowering time, and refer to the relative susceptibility of varieties flowering at the same time. They do not take into account the frost risk associated with when a particular variety will flower given a certain sowing date.

Selecting an appropriate maturity for a particular sowing time is still the best option in limiting damage resulting from frost. Hence the reproductive frost rating needs to be considered in relation to the relative time of sowing and flowering time prediction and frost and heat risk through tools such as DAFWAs Flower Power, www.agric.wa.gov.au/frost/flower-power, or Yield Prophet, www.yieldprophet.com.au.

Continue to select varieties based on the best yield, maturity, agronomic and disease performance from various sources such as regional agronomy trials and the NVTs. Once a variety has been adopted, use the preliminary reproductive frost susceptibility ratings to fine tune frost risk management based on how you currently manage known varieties with a similar rating. For example in southern and Western Australia, Wyalkatchem, which is very susceptible to frost, and Yitpi, which is less susceptible to frost, are managed differently in terms of sowing date, position in landscape and the associated frost risk to maximise production while minimising frost risk. Ensuring that flowering occurs within the optimum flowering window to minimise frost, heat and terminal drought continues to be critical and the reproductive frost ratings need to be used within this context.

When won't the ratings work?

To date, variety differences to susceptibility to frost damage during stem elongation and grain filling have not been confirmed or linked to variation in reproductive frost susceptibility. The reproductive frost ratings are preliminary and currently based on the variation in wheat varieties to maintain grain number under minor reproductive frosts at flowering time. Under these reproductive/floret or head frosts, maintaining grain numbers is the main yield component affected and therefore normally corresponds to yield performance. However, this may not be the case if there is a long growing season or in early sown/flowering crops and varieties that are able to compensate differently through late tillers. Further research is ongoing to validate the relationship between compensation ability, reproductive frost damage and grain yield (DAW00234).

Figure 1. Relationship between minimum temperature and FIS for each wheat tagging event in 2012-2013 across sites in three states, NSW, SA and WA.

Figure 1. Relationship between minimum temperature and FIS for each wheat tagging event in 2012-2013 across sites in three states, NSW, SA and WA.

Figure 2. Range in FIS for 12 frosts events from SA and WA trials in 2012-2013 when the same set of common entries were all tagged at flowering.

Figure 2. Range in FIS for 12 frosts events from SA and WA trials in 2012-2013 when the same set of common entries were all tagged at flowering.

Conclusion

Variation in wheat varieties for reproductive frost susceptibility may be used to manage the frost risk of new varieties after they are adopted, based on how known varieties of similar rating are currently managed. However, selecting varieties should still be primarily based on regional performance information on grain yield, maturity, agronomic and disease performance based on data provided by various regional agronomy groups and NVTs nationally.

Matching flowering through sowing date and variety maturity choice to the appropriate flowering window with appropriate risk of frost and heat should still be used as the main way to limit losses to frost over multiple seasons.

Contact details

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

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

Richard Maccallum
NSW DPI
Condobolin
02 6895 1025
richard.maccallum@dpi.nsw.gov.au

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