Wheat variety reponses to crown rot in southern NSW

Author: | Date: 27 Feb 2013

Andrew Milgate

NSW DPI

GRDC project code: DAN147

Keywords: wheat, crown rot, southern NSW

Take Home Messages

  • Commonly grown wheat varieties in southern NSW do perform differently in the presence of crown rot.
  • Resistance does not guarantee better yield under high disease pressure.
  • Rapid increase in infection can occur within a single season from low starting levels.
  • Non-cereal break crops such as canola, chick peas and lupins may be more profitable than bread wheat in paddocks with medium to high level of inoculum.

Background

During the last 10 years there has been an increase in the intensity of cereals in the cropping rotation and an increase in the adoption of stubble retention farming practices. At the same time, years when moisture stress occurs during grain filling have increased in frequency. The combination of these factors has contributed to an increase in the occurrence of crown rot in wheat and barley in southern NSW. This report summarises some of the recent crown rot trial results from the Integrated Disease Management project for SNSW and NE Vic.

 

Biology of crown rot

Crown rot in southern NSW is caused by both Fusarium pseudograminearum and F. culmorum. There is some evidence that F. culmorum is more common in higher rainfall and irrigated environments. However, both are pathogens of grasses, and therefore, can attack all cereals.

 

Crown rot survives from one season to the next on infected plant material from previous cereal plants and grass weeds. Therefore, stubble management is important in crown rot control. Survival of crown rot is enhanced by dry conditions which limits breakdown of infected plant material during summer or a break crop.

Infection of a new crop is favoured by moist conditions during the winter which enables the fungus to grow from the infected stubble to an adjacent seedling. Once infection has taken place more rapid growth of the pathogen within the plant will occur if the plant becomes moisture stressed.

 

The presence of the pathogen within the stem limits water movement up the plant and when severe, particularly in moisture stressed conditions, results in premature death of the tiller and the presence of the characteristic white (dead) head. Grain does not form in these white heads. Often only single tillers on a plant are infected and white heads are often scattered across a paddock.

 

Variety selection

Resistance is an effective tool against many diseases growers have to confront, such as stripe rust. However in the case of crown rot there are limited varieties with resistance available to choose from. Tolerance is another term used to describe a varieties ability to yield despite infection occurring. We are conducting a series of trials to establish if varieties which have a higher crown rot resistance rating are beneficial in the southern NSW farming region and if the currently grown more susceptible varieties show effective tolerance. The varieties included in the trials and their crown rot resistance ratings are in the Table 1. Varieties were selected to represent the range of resistances and maturities currently available to growers in SNSW.

 

Table 1. Wheat varieties included in the crown rot variety trials in SNSW (Wagga Wagga and Cowra) 2011 – 2012.

Variety

Crown rot resistance rating#

Comment

BELLAROIPBR logo

VS

Durum wheat included as control variety for disease

EGA_GREGORYPBR logo

MS-S

Late spring maturity

EGA_WEDGETAILPBR logo

MS-S

Dual purpose winter wheat

ESPADAPBR logo

S

Mid-maturing spring

EGA_WYLIEPBR logo

MR

Mid-maturing spring

LINCOLNPBR logo

S-VS

Mid-maturing spring

LIVINGSTONPBR logo

MS-S

Mid-maturing spring

WAAGANPBR logo

Not rated

Very quick spring maturity

BOLACPBR logo

S

Late spring type

CRUSADERPBR logo

MS

Quick maturating spring

SUNCO

MR-MS*

Mid-maturing spring

SUNVALE

MS

Mid-maturing spring

# As published in the NSWDPI winter crop variety sowing guide 2011

*Prior to the release of EGA_Wylie,PBR logo Sunco was the most resistant cultivar available for many years

 

The overall site and treatment results show contrasting impacts of crown rot across 2011 and 2012. Figure 1 shows that in the drier spring conditions of 2011 the impact of crown rot was more severe with losses averaged across all varieties of 11% and 25% yield at Wagga Wagga and Cowra respectively. In 2012 however, the losses were 6% and 0.2%. At Cowra in 2012 there was no significant difference between the two treatments. This site received 76 mm of rainfall between August and October and did not experience prolonged periods of moisture stress.

 

In addition to yield we have assessed the extent of crown rot infection that occurred in the varieties (Figure 2). The level of infection was determined by recording basal stem browning incidence on stems collected from a randomly selected 1 metre row within each plot.  In 2011 the level of infection was moderate to low and consistent with the applied treatments. The “plus” treatment plots had significantly higher levels of infection than the untreated “minus” plots. However in 2012 both treatments had high levels of infection at both sites exceeding 90% of tillers infected. This indicates that despite 2012 having low levels of crown rot present at sowing the infection built rapidly during the season so that little difference was detectable by harvest between the treatments.

 

For three sites Wagga 2011, Cowra 2011 and Wagga 2012 there were significant treatment yield effects and also there was a change in ranking of varieties for yield in the two treatments. These results are consistent with NNSW findings that in the presence of crown rot high yielding varieties with lower levels of resistance outperform varieties with better resistance levels. In our trials WaaganPBR logo has the highest yield while EGA_WedgetailPBR logo and EGA_GregoryPBR logo also rate highly. The varieties with better levels of resistance, EGA_WyliePBR logo and Sunco, were amongst the lower yielding varieties in the presence of crown rot. Changing varieties for better crown rot resistance would not be supported by these results. Long term solutions to reduce crown rot inoculum will rely on rotations with non-host crops such as canola, lupins or peas.

Figure 1. Crown rot trial treatment yield effects in 2011 and 2012 at two locations in SNSW.

Figure 1. Crown rot trial treatment yield effects in 2011 and 2012 at two locations in SNSW. Treatments are “plus_CR” seed inoculated with crown rot spores prior to sowing and “minus_CR” seed sown without inoculation. LSD bars displayed in the graph indicate a significant difference between means where the any mean and the bar do not overlap.

Figure 2. Crown rot trial treatment infection effects measured as basal stem browning incidence in 2011 and 2012 at two locations in SNSW.

Figure 2. Crown rot trial treatment infection effects measured as basal stem browning incidence in 2011 and 2012 at two locations in SNSW. Treatments are “plus_CR” seed inoculated with crown rot spores prior to sowing and “minus_CR” seed sown without inoculation. LSD bars displayed in the graph indicate a significant difference between means where the any mean and the bar do not overlap.

Figure 3. Crown rot trial variety effects measured as yield (t/ha) in 2011 and 2012 at two locations in SNSW.

Figure 3. Crown rot trial variety effects measured as yield (t/ha) in 2011 and 2012 at two locations in SNSW. Treatments are “plus_CR” seed inoculated with crown rot spores prior to sowing and “minus_CR” seed sown without inoculation. LSD bars displayed in the graph indicate a significant difference between means where the any mean and the bar do not overlap.

 

Assessing the risk

Being able to assess the risk of disease development is an important tool for effective management. The amount of stubble infection at harvest or prior to sowing has been suggested as a way in which growers can determine their level of crown rot risk. To examine this we set up two trials in 2012 to see if this was useful in SNSW. The trials were established by measuring the amount of stubble infection as basal browning at harvest in 2011 then sowing two varieties in to the standing stubble in 2012 then measuring the amount of basal stem browning at harvest. The results of the infection at harvest in 2012 are presented in Figure 4 plotted against the level of infection in 2011. This figure shows that from very low levels of crown rot being present at harvest in 2011 the plants at harvest in 2012 had reached almost 100% of stems/tillers infected. This was a rapid build up of the disease in one season and demonstrates the disease’s potential to cause problems in tight springs.

 

These results contrast to previous findings in Victoria and will require validation in the current season as we continue to monitor what happens to the level of inoculum and its ability to infect plants in 2013.

Figure 4. Stubble infection of crown rot oversown trials at Wagga (●) and Cowra (▲) in 2011 and 2012 in SNSW.

Figure 4. Stubble infection of crown rot oversown trials at Wagga (●) and Cowra (▲) in 2011 and 2012 in SNSW.

Conclusions

  • Current varieties with higher resistance ratings don’t offer better yield in the presence of crown rot.
  • Know your crown rot risk, the disease can increase rapidly within a season.
  • Establish base line data to monitor inoculum levels in suspect paddocks.
  • Early management decisions are the key to minimising losses.
  • Rainfall in spring will play a big part in determining the extent of yield loss in infected paddocks.
  • Non-host crops will reduce inoculum levels but this may take more than one year.

 

 

Useful Reference

Crown Rot in Cereals Fact Sheet, GRDC

http://www.grdc.com.au/uploads/documents/GRDC_CrownRot_SthWest.pdf

 

Contact Details

Andrew Milgate

NSW DPI

02 6938 1990

andrew.milgate@dpi.nsw.gov.au

GRDC Project Code: DAN147,