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Investigation of post head-emergence frost resistance in several CIMMYT synthetic and Queensland wheats

Troy M. Frederiks1, John T. Christopher1 and Andrew K. Borrell2

1 Queensland Department of Primary Industry and Fisheries, Leslie Research Centre, PO Box 2282, Toowoomba, QLD 4350,
Email troy.frederiks@dpi.qld.gov.au
2
Queensland Department of Primary Industry and Fisheries, Hermitage Research Station, via Warwick, QLD 4370.
Email andrew.borrell@dpi.qld.gov.au

Abstract

Frost damage, specifically spring type radiation frosting of wheat post head-emergence, is a signifcant problem locally and internationally. Despite decades of intensive screening, negligible increases in frost resistance have been found. Some years ago, CIMMYT identified several synthetic wheat lines with putative increases in resistance. This project set out to quantify any useful (from a plant breeding perspective) frost resistance in available CIMMYT synthetics and several Queensland (QLD) lines. Our screening method allowed frost resistance to be accurately assessed in isolation from frost escape mechanisms. Using this method, severe universal damage was observed in all wheat material at crop temperatures less than –6 C. At no time during this study did any of the putative resistant material show signs of damage limitation when directly compared to control lines. Of particular interest, a unique frost event at the Kingsthorpe site on the 20th of July 2001, caps the maximum, if any, increase in tolerance exhibited by this material to 0.4 C ( 0.4 C temperature sensor accuracy). All the tested wheat lines with putative frost resistance proved to be very long season wheats. This suggests that at least some of the putative frost resistance was probably due to frost escape rather than true frost resistance.

Media summary

Synthetic hexaploid wheats and specifically developed lines are being tested for resistance to radiant spring frosts that cause significant yield losses in wheat post head-emergence.

Key Words

Post head-emergence frost; wheat; frost resistance, radiant frost

Introduction

Although many elite winter wheats are tolerant to temperatures of –20 C in the vegetative stages, wheat suffers severe damage at much more moderate temperatures during the reproductive period. Unfortunately, this is equally true of both winter and spring type wheat. Post head-emergence frost damage is a significant problem in Australia and several other regions including the Mediterranean and South America. The problem occurs in areas where the heat and drought of summer restrict the main growing season to the late winter and spring, where daytime temperatures are ideal for growth, but night temperatures can fall to damaging levels. Paradoxically, crops grown in warmer climates are at greater risk of injury due to faster development and rapid progression through to the susceptible reproductive stages (Single 1964, 1988 & 1984).

In Queensland and northern New South Wales, yield reductions due to spring radiation frosting of winter cereals are significant due to (1) direct damage and (2) late planting. Direct damage often causes 100% yield losses to affected heading crops. It is estimated that this results in a 10% reduction in long-term average yield, even under best management practices. To minimise the likelihood of crop losses, farmers attempt to time planting so that crops will flower and mature later when the likelihood of frost is reduced. Unfortunately, this increases the likelihood of water stress in the later stages due to low rainfall combined with rapidly rising temperatures and potential evaporation (or vapour pressure deficits). The average yield loss associated with this late flowering is in the order of 1 to 1.5 % for each day flowering is delayed past an optimum flowering date (early August in QLD; Woodruff & Tonks 1983; Woodruff 1988). Yield increases of 0.8 t/ha have been observed when early flowering crops in central QLD have escaped frost (Woodruff pers. com.). This increase in yield can routinely be in the order of 50% of long-term average yields. The risk of spring radiation frost damage also prevents growers from utilising early planting opportunities when a “quick” variety would flower during the period of maximum frost risk but a slower type may exhaust stored soil moisture too early in development. As planting opportunities are limited, missed plantings represent a further potential for losses.

If wheat post head-emergence were able to withstand frosts of 2 C lower than at present, crop losses would be considerably reduced. In areas of southern Australia with a Mediterranean climate, the occurrence of frost damage could be reduced from 1 year in 10 on average to less than 1 year in 50. In the north, cropping systems would be revolutionised. The effect on losses due to direct damage would be similar to that in southern Australia. However, even greater yield increases would be expected through earlier flowering.

Thus, increased post head-emergence frost resistance for winter cereals in Australia is an important objective. Frost resistance has been the focus of investigation for more than a century (Farrer, W. 1900 in Single 1985). Despite increased yield through better management of frost risk, very little true genetic gain has been made. There have been a number of instances where lines with putative post head-emergence frost resistance have been identified opportunistically when field trials have been affected by natural frosts. To date, material identified using this approach has failed to produce a resistant variety. This may be due to very small differences in phenology determining whether a particular line is exposed to a frost event. In order to minimise wasted research effort, a screening method that can conclusively identify post head-emergence frost resistance is required.

The objectives of this study are to quantify the level of resistance to post head-emergence frost in several CIMMYT synthetic wheat lines with putative increases in tolerance (Maes et. al. 2001) and several lines developed specifically by David Woodruff in Queensland. In addition, a method of determining the damage caused to specific heads known to have been exposed during characterised frost events was further refined.

Methods

Field trials were conducted in the winter seasons 1999, 2000, 01, 02 and 03. Where possible, plantings were established at four different planting dates at two field sites: Hermitage Research Station, Warwick, and the DPIF experimental farm, Kingsthorpe. Supplemental lighting was used to generate a range of flowering times within each planting. A purpose designed and built frost cover was used on a replicate of the trial at the Hermitage Research Station in the 2000/01/02 seasons. The cover acted to moderate the effects of severe frosts. Site and plant temperature data was recorded continuously using thermocouples attached to Gemini data loggers. Several frost events were experienced each field season at each site.

Following frost events, both qualitative and quantitative data on plant damage, was collected. Individual heads that had been exposed to the particular frost were tagged as soon as practical following the frost event so they could be assessed later as symptoms developed. This particular screening methodology was developed in order to identify heads of known developmental stage that had been exposed to particular frost events. Care was taken wherever possible to standardise temperature profiles, ice-nucleation and frost formation. The accurate marking of individual heads is among the most important features of this screening methodology as it allows true frost resistance to be separated from frost escape mechanisms.

The CIMMYT synthetic wheats screened in this study were CIGM89.559; CIGM90.846; CIGM90.863; CIGM92.1723; CIGM92.1721; CIGM93.261 and five lines developed by David Woodruff in Queensland. The lines were compared to standard controls including Kite and Hartog. Barley provided from the University of Adelaide and other grass species were also screened, although only the results for wheat are presented.

Results and Discussion

The winter seasons of 2000, 2001 and 2002 were characterised by low rainfall with eighteen frosts where head temperatures reached less than -4.5 C. Severe universal damage was observed in all wheat material at crop temperatures less than –6 C (Table 1). This trend was observed for all frost events in all years at both field sites. At no time during this study did any of the putative resistant CIMMYT synthetics, or the specifically developed Woodruff lines, show signs of damage limitation, post head-emergance, when directly compared to control lines.

Table 1. Absolute minimum temperatures measured across the Kingsthorpe trial during frost events in 2001. Minimum temperatures that resulted in severe universal damage to all post head-emergence wheat lines tested are indicated in bold. Frosts of –6 C or below resulted in severe universal damage.

Date

May

June

July

August

Sept.

13

25

11

16

9

20

1

10

18

3

Min. temp. C

-3.3

-6

-1.1

-8.8

-8

-6.8

-0.5

-8.1

-7.5

-3.5

One specific frost event at the Kingsthorpe site on the 20th of July 2001 is particularly noteworthy (Figure 1). The data for this event suggests that any increase in frost resistance is less than or equal to 0.4C ( 0.4C temperature sensor accuracy). This frost produced differential damage and temperatures across strictly controlled trials at the Kingsthorpe site. Severe universal damage was observed in the colder trial. In contrast universal damage limitation was observed in the slightly warmer (0.4C 0.4C) trial. Therefore the temperature differential observed between these trials represents the maximum level of increased tolerance for the putative tolerant lines, as compared to controls (i.e. Kite). The subtle difference in temperature between trials was likely due to differences in canopy density photoperiod extension. The thinner canopy of the later planting allowed long wave radiation from the soil to reach the emerged heads and similarly allowed cold air in contact with these heads to drain away more efficently (Woodruff et. al. 1997). It is unlikely that selection systems can be devised to reliably select for lines with an increased frost resistance of only 0.4C.

Figure 1. Minimum temperature plot for (a) 2001 and (b) 20th July 2001, in particular. The event on the 20th July produced differential damage between plants that were sown at 2 different dates but were flowering during the frost due to photoperiod extension using supplemental lighting in the later planting. The earlier planted trial without photoperiod extension reached a minimum temperature of -6C (solid trace). In contrast, a similar but later planting with photoperiod extension reached a minimum temperature of –5.6C (stipled trace).

All the tested synthetic wheat lines from CIMMYT with putative frost tolerance proved to be very long season wheats. This suggests that at least some of the putative frost resistance may be due to frost escape rather than frost resistance.

As outlined in the introduction, post head-emergence frost tolerance in winter cereals is an important area of research in Australia. However, the results of this study suggest that preliminary encouraging reports of new sources of frost resistance should be viewed with some caution, reflecting on the difficulty of frost as a phenomenon, and the problems associated with screening. Results must be confirmed using methods that record damage to individual heads known to have been exposed to a characterised frost event in order to separate the effects of small phenological differences from true frost resistance. Screening of further sources of putative frost resistance is continuing. In an attempt to increase the likelihood of finding useful resistance, the search has now been broadened to include relatives of wheat and other grass species.

Acknowledgements

The Grains Research and Development Corporation provided the financial support for this work. I would also like to take this opportunity to acknowledge the efforts of David Woodruff (Senior Principal Crop Physiologist, LRC, QDPI). Mr Woodruff initiated and led this project until his retirement in June 2001.

References

Maes B, Trethowan R, Reynolds M, van Ginkel M and Skovmand B (2001). The influence of glume pubescence on spikelet temperature of wheat under freezing conditions. Australian Journal of Plant Physiology 28, 141-148.

Single W (1964). Studies on frost injury to wheat. Australian Journal of Agricultural Research 15, 869-875.

Single W (1984). Frost Injury and the Physiology of the Wheat Plant. The Journal of the Australian Institute of Agricultural Science 51, 128-134.

Single W (1985). Frost Injury and the Physiology of the Wheat Plant. The Journal of the Australian Institute of Agricultural Science 51, 128-134.

Single W (1988). In ‘Frost Injury of Wheat’, A Workshop of the Wheat Research Council, pp. 7-18.

Woodruff D and Tonks J (1983). Relationship between Time of anthesis and Grain Yield of Winter Genotypes with Differing Developmental Patterns. Australian Journal of Agricultural Research 34, 1-11.

Woodruff D (1988). In ‘Frost Injury of Wheat’. A Workshop of the Wheat Research Council, pp. 33-42.

Woodruff D, Douglas N and French Vic (1997). Frost Damage in Winter Crops. The State of Queensland Department of Primary Industries, Brisbane.

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