Yield impact of crown rot and sowing time on winter cereal crop and variety selection Tulloona 2015

Take home message

• Sowing date and variety maturity choice is a balance between the risk of frost versus terminal heat stress
• Earlier sowing can increase frost risk but also generally maximises yield potential and reduces the extent of yield loss from crown rot
• Cereal crop and variety selection can have a significant impact on yield in the presence of high levels of crown rot infection
• Durum wheat and barley or bread wheat varieties with increased susceptibility to crown rot should only be grown in paddocks known to have low risk inoculum levels based on testing (e.g PreDicta B®)
• All winter cereal varieties are susceptible to crown rot infection and will not significantly reduce inoculum levels for subsequent crops. Cereal crop and/or variety choice is not the sole solution to crown rot.

Background

Crown rot, caused predominantly by Fusarium pseudograminearum (Fp), is a major constraint to winter cereal (wheat, barley and durum) production in northern NSW and southern QLD. All winter cereal crops host the crown rot fungus. Yield loss varies between winter cereal crops with the approximate order of increasing loss being oats, barley, triticale, bread wheat and durum. Crown rot infection is characterised by a honey-brown discolouration at the base of infected tillers. Yield loss is related to the expression of whiteheads which are induced by moisture and/or temperature stress during flowering and grain-filling. Previous NSW DPI research has demonstrated that earlier sowing can reduce the expression of crown rot by bringing the grain-fill period forward when temperatures are generally lower. Earlier sowing also theoretically facilitates increased root growth early in the season, which may result in deeper root exploration and improved access to soil moisture.

Evapotranspiration stress during grain-filling can also be manipulated by the relative maturity of crop type and variety choice. Variety maturity interacts with the expression of crown rot which is dependent on the timing of stress within a given season and the relative stage of development of a variety. In the northern grain region, sowing time and variety maturity need to be balanced against the risk of excessive early vegetative growth depleting soil moisture reserves prior to grain-fill, and the risk of frost versus terminal heat stress during flowering and grain development. The impact of crown rot on yield and grain quality was examined in a range of durum, bread wheat and barley varieties across two sowing times near Tulloona in north-west NSW in 2015.

Tulloona - 2015

A replicated crown rot yield loss trial was conducted near Tulloona in 2015 and included 24 barley, 5 durum and 19 bread wheat entries (Figure 1) sown at two different dates. The trial used an inoculated versus uninoculated trial design, to evaluate the relative yield response of varieties to crown rot infection across the two sowing times. The first time of sowing (ToS 1) was the 6^th May 2015 while the second sowing time (ToS 2) was 4^th June 2015. The site had 137 kg/ha of available nitrate N (0-120 cm) at sowing. An additional 90 kg N/ha was applied as urea at sowing, with 70 kg/ha of Granulock Z starter fertilizer also applied to each plot.

The site was soil cored prior to sowing (separate bulk samples across each range) to determine background pathogen levels using the DNA based soil test PreDicta B. Crown rot inoculum levels were at a medium risk level (2.0 log Fusarium DNA/g soil) and populations of the root lesion nematode (RLN) Pratylenchus thornei (Pt) were medium (2.5 Pt/g soil) while P. neglectus were below detection limit across the Tulloona trial site at sowing in 2015. Pt are widespread across the northern grains region and feed inside the root systems of susceptible varieties and crops which can impact on grain yield potential. Furthermore, in winter cereals Pt can also exacerbate the expression of crown rot and hence increase the extent of yield loss.

Impact of sowing time

Yield was reduced from 5.11 t/ha with ToS 1 down to 4.23 t/ha with ToS 2 in the no added CR treatment when averaged across the full 48 winter cereal entries. This represented a 17% (0.89 t/ha) reduction in yield potential with a delayed sowing of four weeks. In the presence of high levels of crown rot infection (added CR) average yield across entries was reduced from 4.76 t/ha with ToS 1 down to 3.33 t/ha with ToS 2, which represented a larger 30% (1.42 t/ha) reduction in yield potential associated with delayed sowing. This was due to a considerably higher average level of yield loss associated with increased crown rot infection of 21% (0.89 t/ha) with later sowing (ToS 2) compared to an average of only 7% (0.35 t/ha) with ToS 1.

Cereal crop and variety differences – ToS 1 (6^th May 2015)

Figure 1. Impact of crown rot on the yield of 24  barley, 5 durum and 19 bread wheat entries sown on the 6th May - Tulloona 2015

Frost did negatively impact on the yield of quicker maturing durum and bread wheat varieties in ToS 1 (Figure 1). Frost damage was most noticeable in Jandaroi  and DBA Lilllaroi  in the durum entries and with LRPB Dart in the bread wheat. In the no added CR treatment yield ranged in the barley entries from 6.26 t/ha with the recently released feed variety Rosalind down to 3.98 t/ha with Scope CL, in the durum from 5.74 t/ha with DBA Aurora down to 1.89 t/ha with Jandaroi (frosted), and in bread wheat from 6.14 t/ha with the advanced breeding line QT15406R down to 3.28 t/ha with LRPB Dart (frosted) (black bars, Figure 1).

Yield loss associated with high levels of crown rot infection is measured as the difference between the no added CR (black bar) and added CR (grey bar) treatments (Figure 1). Added CR significantly reduced yield in only four of the barley entries by 15% in Navigator (0.81 t/ha) and SY Rattler (0.82 t/ha), 16% in Urambie (0.77 t/ha) and 17% in Commander (0.95 t/ha) in ToS 1 (Figure 1). Yield loss from added CR was not significant with any of the five durum entries with ToS 1 but remember that the yield potential of quicker maturing varieties was impacted by frost. Ten of the 19 bread wheat entries (Beckom, Viking, Elmore CL, Suntop, Suntime, EGA Eaglehawk, QT15406R, LRPB Flanker, Sunmate and EGA Gregory) suffered signficant levels of yield loss with added CR infection in ToS 1 which ranged from 10% (0.57 t/ha) in Beckom up to 23% (1.31 t/ha) with EGA Gregory (Figure 1).

Cereal crop and variety differences – ToS 2 (4^th June 2015)

No frost damage was evident in any of the winter cereal entries when sowing time was delayed to the 4^th June in 2015. In the no added CR treatment yield ranged in the barley entries from 5.04 t/ha with the advanced breeding line W14896 down to 3.31 t/ha with Gairdner, in the durum from 4.76 t/ha with DBA Aurora down to 4.21 t/ha Caparoi, and in bread wheat from 4.80 t/ha with with Livingston down to 3.40 t/ha with EGA Eagkehawk (black bars, Figure 2).

Figure 2. Impact of crown rot on the yield of 24  barley, 5 durum and 19 bread wheat entries sown on the 4th June - Tulloona 2015

Added CR caused significant levels of yield loss in 19 of the 24 barley entries (except Rosalind, IGB1334T, W14897, La Trobe and Hindmarsh) and ranged from 12% in Shepherd (0.54 t/ha) up to 30% in Admiral (1.07 t/ha) in ToS 2 (Figure 2). The five durum entries all suffered relatively high and significant levels of yield loss with added CR in ToS 2, with no difference between entries. Yield loss ranged from 32% in the advanced durum breeding line 190873 (1.47 t/ha) up to 35% in DBA Aurora (1.65 t/ha). Fifteen of the 19 bread wheat entries (except LRPB Dart, Sunguard, LRPB Lancer and Elmore CL) suffered signficant levels of yield loss with added CR infection in ToS 2 and ranged from 17% (0.75 t/ha) in Mitch up to 37% (1.64 t/ha) with LRPB Flanker (Figure 2).

Concentrating purely on the extent of yield loss associated with crown rot infection in the different varieties can potentially be misleading as entries can vary markedly in their actual yield potential in a given environment and season. Amongst the bread wheat entries, Sunguard and LRPB Lancer had the lowest percentage yield loss from crown rot when sown on the 4^th June (ToS 2) at Tulloona in 2015. However, in the absence of added CR (black bars) Sunguard was significantly lower yielding than Livingston (0.70 t/ha), Condo (0.59 t/ha), and the two numbered lines LPB09-0358 and QT15406R (0.58 t/ha) (Figure 2). LRPB Lancer similarly in the no added CR treatment with ToS 2 was between 0.99 t/ha to 0.53 t/ha lower yielding than the bread wheat entries Livingston, Condo, LPB09-0358, QT15406R, Suntop, Mitch, LRPB Flanker, Beckom and LRPB Dart at Tulloona in 2015. Hence, selecting a variety on the basis of reduced yield loss to crown rot should not come at the expense of yield potential at the targeted sowing time.

Another option for evaluating the data is to concentrate on the absolute yield achieved under high disease pressure in the added CR treatments at each sowing time (grey bars; Figure 1 and 2). Under high crown rot pressure with ToS 1 (6^th May) only three barley varieties (Urambie, Westminster and Scope CL) were lower yielding than Commander (range 0.59 to 0.71 t/ha) while 11 barley entries (Fairview to Rosalind) were higher yielding than Commander (range 0.60 to 1.39 t/ha; Figure 1). Due largely to frost in the durum entries with ToS 1, DBA Lillaroi (0.74 t/ha) and Jandaroi (1.97 t/ha) were significantly lower yielding than Caparoi, while DBA Aurora was 1.17 t/ha higher yielding than Caparoi in the added CR treatment. With the bread wheat entries in ToS 1, only the severely frost affected variety LRPB Dart was lower yielding (0.95 t/ha) than the widely grown variety EGA Gregory, while 12 entries (Elmore CL to LPB09-0358) were higher yielding than EGA Gregory (range 0.57 t/ha to 1.31 t/ha; Figure 1).

The impacts of high levels of crown rot infection on yield were considerably greater with the later sowing time of the 4^th June (ToS 2) but significant yield benefits were still apparent with potential crop and variety selections. Under high crown rot pressure with ToS 2, ten barley varieties (Schooner to Admiral) were lower yielding than Commander (range 0.56 to 1.33 t/ha) while only two barley entries (IGB1334T and Rosalind) were higher yielding than Commander (range 0.55 to 0.77 t/ha; Figure 2). There was no significant difference in the yield of the five durum entries under high levels of crown rot infection in ToS 2. With the bread wheat entries in ToS 2, only the long season entry EGA Eaglehawk was lower yielding (0.74 t/ha) than EGA Gregory, while nine entries (Elmore CL to LRPB Dart) provided a significant yield benefit over EGA Gregory (range 0.57 t/ha to 1.05 t/ha; Figure 2) in the presence of added CR.

Implications

In the northern grain region, sowing date and variety maturity choice is a balance between the risk of frost versus terminal heat stress. Both can have a significant impact on grain yield as highlighted at Tulloona in 2015. Frost risk needs to be kept in perspective and sowing date matched to the relative maturity of a chosen variety. A very conservative approach to frost risk, based on recent experience, runs the risk of pushing grain-fill too far into warmer conditions. This can reduce yield by itself but if there is also an underlying issue with crown rot, then delayed sowing significantly exacerbates the expression of this disease with negative impacts on both yield and grain quality.

Winter cereal crop types and varieties do differ in their extent of yield loss from crown rot infection. Hence, production of more susceptible cereal crop types such as durum wheat or bread wheat varieties such as EGA Gregory needs to be targeted at low risk paddocks based on either stubble or DNA testing such as PreDicta B. Unfortunately, grain quality data was not available at the time of writing this update paper and should be included in any variety selection considerations.

Barley is generally considered more tolerant (reduced yield impact) of crown rot than bread wheat as it tends to largely escape severe evapotranspiration stress, which exacerbates expression, by maturing earlier. However, this trial highlights that this escape mechanism is dependent on sowing time with barley entries suffering an average yield loss from crown rot of 18% on the later sowing time (4^th June) relative to only 6% with the earlier timing (6^th May). Barley is very susceptible to infection by the crown rot fungus, and if sown later in its planting window will be trying to fill grain under warmer conditions which can lead to significant yield loss from crown rot. This interaction is also generally more pronounced in varieties with longer maturity such as Oxford barley, which did not have significant yield loss in the earlier sowing date but suffered 26% yield loss from crown rot infection with delayed sowing.

If forced into planting a cereal crop in a high crown rot risk situation then some barley varieties may provide a yield advantage over bread wheat in that season, provided early stress does not occur and the escape mechanism is not lost through delayed sowing. Some of the newer bread wheat varieties do appear to be closing this gap to some extent. However, a key message is that this decision is only potentially maximising profit in the current season. Growing barley over bread wheat will not assist with the reduction of crown rot inoculum levels, as barley is still very susceptible to infection. Significant yield loss can still occur in the best of the barley and bread wheat varieties in the presence of high crown rot infection. Crop and variety choice is therefore not the sole solution to crown rot but rather just one element of an integrated management strategy to limit losses from this disease.

Acknowledgments

The research undertaken as part of projects DAN00175 and DAN00167 is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC.  The authors would like to thank them for their continued support. This project is co-funded by the Government of NSW through the NSW DPI who are also thanked for their support in fully funding two of our positions and for laboratory and other infrastructure costs. Soil-borne pathogen levels were determined using the DNA based soil test service PreDicta B provided by the South Australian Research and Development Institute. Technical assistance provided by Stephen Morphett, Jim Perfrement, Jan Hoskings, Mick Del Santo, Robyn Shapland and Patrick Mortell is gratefully acknowledged. We finally thank Jack and Julia Gooderham for allowing us to conduct this trial on their property ‘Myling’ near Tulloona in 2015.

Contact details

Rick Graham
NSW DPI, Tamworth
Mb: 0428 264 971
Email: rick.graham@dpi.nsw.gov.au

Steven Simpfendorfer
NSW DPI, Tamworth
Mb: 0439 581 672
Email: steven.simpfendorfer@dpi.nsw.gov.au