High crown rot risk - barley vs wheat

Take home message

• In 57% of trial comparisons Commander barley provided a significant yield benefit (av. 0.95 t/ha) over the bread wheat variety EGA Gregory.
• In 30% of trial comparisons the effect of choosing Commander or EGA Gregory was neutral.
• In 13% of trial comparisons Commander resulted in a significant yield penalty (av. 0.48 t/ha) compared to growing EGA Gregory, likely due to stress occurring earlier in the season.
• Barley and bread wheat varieties do vary in yield response in the presence of crown rot infection.
• Barley is very susceptible to crown rot infection and will not reduce inoculum levels for subsequent crops.

Introduction

NSW DPI has pioneered the evaluation of relative yield responses of bread wheat, durum and barley varieties to crown rot across the northern grains region, using an inoculated versus uninoculated trial design since 2004. Yield loss trials conducted across 11 sites in northern NSW in 2007, in collaboration with the Northern Grower Alliance (NGA), found that the average yield loss from crown rot was 20% in barley (4 varieties), 25% in bread wheat (5 varieties) and 58% in durum (EGA Bellaroi).

Over this time awareness has also increased about the distribution and importance of root lesion nematodes, predominantly Pratylenchus thornei (Pt), across the northern region and its interaction with the expression of crown rot. This has raised the issue of the relative impact of crown rot and Pt on wheat relative to barley and which is the better rotation option if a moderate to high disease risk situation cannot be avoided. Consideration needs to be given to yield in the current season but also potential consequences for the rotation in subsequent years. This paper is focused solely on crown rot. NGA and USQ (formerly DAFFQ) have covered the relative resistance and tolerance of wheat and barley to Pt at current or previous GRDC updates.

Yield in the presence of crown rot

Between 2009 and 2014 NSW DPI has conducted 20 replicated small plot field trials where both the bread wheat variety EGA Gregory, a widely grown cultivar across the region, and the barley variety Commander were included (Table 1). All trials had an inoculated vs uninoculated trial design with two separate sowing dates in five of the trials. If the interaction of sowing date was significant then data from both dates is presented but the average yield result across both planting times is outlined if the effect of sowing time was not significant. In total this provides 23 comparisons between EGA Gregory and Commander across seasons. As the interest is in the relative performance of barley versus wheat in the presence of crown rot infection, only yield results from treatments inoculated with crown rot are presented. Consequently, this is a comparison across sites and years under high crown rot pressure. The emphasis is also on the actual yield achieved under these high infection levels rather than the percentage yield loss from crown rot. This is warranted as yield is what largely drives profitability for growers.

In 13 of 23 comparisons (57%) Commander provided a yield benefit over growing EGA Gregory (range +0.28 to +2.20 t/ha; av. +0.95 t/ha) (Table 1). In 7 of 23 comparisons (30%) the difference in yield between Commander and EGA Gregory was not significant (ns). In three comparisons (13%) Commander was actually significantly lower yielding than EGA Gregory (range -0.33 to -0.77 t/ha, av. -0.48 t/ha). In 2011 at both sites, mild conditions in terms of temperature and adequate soil moisture limited the expression of crown rot with no significant yield difference between inoculated and uninoculated treatments. In all other trials seasonal conditions favoured varying but significant levels of crown rot expression.

Table 1. Yield of barley cv. Commander compared to wheat cv. EGA Gregory in NSW DPI trials inoculated with crown rot from 2009-2014

Barley is generally considered more tolerant (reduced yield impact) of crown rot than bread wheat as it tends to escape severe evaporative stress, which exacerbates expression, by maturing earlier. However, as the two sowing times at Garah in 2013 highlighted, this escape mechanism is dependent on sowing time with all four barley varieties in the trial (including Commander) suffering a much higher percentage yield loss from crown rot on the later sowing time (20-30%) relative to the earlier timing (6-11%)(data not shown). Barley is very susceptible to infection by the crown rot fungus and if sown later in its planting window will be filling grain under hotter conditions that can still lead to significant yield loss from crown rot. However, in this situation Commander is still likely to yield higher than EGA Gregory (e.g. Coonamble 2009, Tamworth 2009 and 2014, Bithramere 2014).

What about newer wheat and barley varieties?

Recent research conducted by NSW DPI across 11 sites in 2013 and 12 sites in 2014 has highlighted that some of the recently released bread wheat varieties (e.g. Suntop, Sunguard and LRPB Spitfire) produce higher yield in the presence of crown rot infection than the widely grown, but more susceptible variety, EGA Gregory. Data on the relative yield of barley varieties in the presence of crown rot is more limited.

Replicated trials were conducted at Tamworth and Garah in 2014 where a range of barley and wheat varieties were evaluated for their relative yield loss in the presence of high levels of crown rot infection. Similar to previous research the impact of crown rot on yield was determined through the comparison of yield between plots inoculated or uninoculated with crown rot at sowing.

Tamworth 2014

Crown rot infection caused yield loss in the barley varieties ranging from 10% in La Trobe up to 29% in Oxford. In the bread wheat varieties yield loss ranged from 14% in LRPB Spitfire up to 23% in EGA Gregory. However, there were low-moderate background levels of crown rot across the site which potentially reduced the differences in yield loss. Hence, only the actual yield of each variety measured in the inoculated treatment (high infection level) is presented (Figure 1).

Figure 1. Yield of seven barley and seven bread wheat varieties in the presence of high crown rot infection – Tamworth 2014
(Values are the average of 20^th May and 10^th June sowing dates; bars followed by the same letter are not significantly different at the 95% confidence level)

With the exception of Oxford, all barley varieties were higher yielding than EGA Gregory in the presence of high levels of crown rot infection (Figure 1). The reduced biomass barley plant types, Hindmarsh and La Trobe produced higher yield than the other barley varieties being 0.71 t/ha and 0.72 t/ha higher yielding than Commander, respectively.

All of the newer wheat varieties were higher yielding than EGA Gregory in the presence of high levels of crown rot infection. Suntop (0.73 t/ha), Sunguard (0.74 t/ha) and LRPB Spitfire (0.85 t/ha) provided the greatest yield advantage over EGA Gregory (Figure 1). However, even the best bread wheat variety (LRPB Spitfire) was between 0.51 to 1.32 t/ha lower yielding than all of the barley varieties, except Oxford.

Garah 2014

Garah was a considerably lower yielding site than Tamworth in 2014 due to the lack of any stored soil moisture at sowing and only ~80 mm of effective in-crop rainfall. Encouragingly,  the trends in varietal yield performance in the presence of crown rot were fairly consistent with Tamworth, even though they were separated by around 350 km in a roughly  north-west direction.

Crown rot infection caused yield loss in the barley varieties ranging from 17% in Hindmarsh up to 31% in GrangeR. In the bread wheat varieties yield loss ranged from nil in LRPB Lancer up to 40% in EGA Gregory. Actual yield of each variety measured in the inoculated treatment (high infection level) is presented below (Figure 2).

Figure 2. Yield of seven barley and seven bread wheat varieties in the presence of high crown rot infection – Garah 2014
(Values are the average of 2^nd May and 12^th June sowing dates; bars followed by the same letter are not significantly different at the 95% confidence level)

With the exception of Oxford and GrangeR, all barley varieties were higher yielding than EGA Gregory in the presence of high levels of crown rot infection (Figure 2). Compass (0.29 t/ha), La Trobe (0.38 t/ha), Fathom (0.38 t/ha) and Hindmarsh (0.54 t/ha) produced higher yields than Commander (Figure 2).

Suntop (0.29 t/ha), Sunguard (0.30 t/ha) and LRPB Lancer (0.52 t/ha) provided significant yield advantage over EGA Gregory (Figure 2). The best barley variety Hindmarsh was 0.30 t/ha higher yielding than the best bread wheat variety LRPB Lancer. Interestingly, three of the better options at Garah in 2014 were the reduced biomass plant types La Trobe and Hindmarsh and the bread wheat variety LRPB Lancer.

What about the build-up of crown rot inoculum?

Barley is very susceptible to infection by the crown rot fungus. It does not have improved resistance to crown rot infection. Barley tends to yield better in the presence of crown rot infection due to its earlier maturity relative to bread wheat, providing an escape mechanism which reduces its exposure to evaporative stress during the critical grain filling stage. This is often referred to as tolerance. To some extent this may also be why the barley variety Oxford, which has a longer maturity, does not yield as well as other barley varieties in the presence of crown rot infection.  The tolerance mechanism is lost through the delayed maturity. It is CRITICAL that growers do not continue to confuse tolerance with resistance when considering crown rot. Barley is likely to provide a yield advantage over wheat in the presence of high crown rot infection but it will not reduce inoculum levels for subsequent crops.

Implications

Interestingly, three of the better options at Garah in 2014 were the reduced biomass barley plant types La Trobe and Hindmarsh and the bread wheat variety LRPB Lancer. These reduced growth habits may provide a yield advantage under lower yielding situations in the northern region as they potentially conserve soil water usage for grain-fill. This may also reduce the expression of crown rot and the impact of this disease on yield. These varieties also produced respectable yield in the presence of high crown rot infection at Tamworth in 2014 which had a much higher yield potential.

The crown rot fungus is believed to be triggered by moisture/temperature stress to proliferate in the base of infected tillers which results in constriction of the xylem (water transport structure in stems) and results in the production of whiteheads. However, the crown rot fungus does not care what time of year it is when the stress occurs. If there is limited stored soil moisture and relatively high temperatures at earlier growth stages then the crown rot fungus will still proliferate which can reduce biomass production and even kill plants. This has been particularly noticeable in commercial durum and barley crops in the northern region in previous seasons and was evident in inoculated plots of Commander at Terry Hie Hie and Macalister in 2014. This is the likely reason for the negative yield response of Commander compared to EGA Gregory in the presence of crown rot infection at these sites in 2014.

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, as long as early stress does not occur. 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 very susceptible to infection. Barley as a general rule also produces increased stubble loads compared to wheat so could actually be building up increased crown rot inoculum levels.

Significant yield loss is still occurring 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

All of this research was co-funded by NSW DPI and GRDC under projects DAN00175 and DAN00167. Assistance provided by Robyn Shapland, Finn Fensbo, Patrick Mortell, Kay Warren, Tara Burns, Karen Cassin, Paul Nash, Stephen Morphett, Matthew Gardner, Jim Perfrement, Patrick Mortell, Peter Formann and Rod Bambach (all NSW DPI) for sowing, maintaining and harvesting many of the trials over the years is greatly appreciated. We are further extremely thankful to NVT operators for conducting some trials and co-operating growers for use of their paddocks.

Contact details

Dr Steven Simpfendorfer
NSW DPI
Ph: 0439581672
Email: steven.simpfendorfer@dpi.nsw.gov.au

Rick Graham
NSW DPI
Ph: 0428264971
Email: ricky.graham@dpi.nsw.gov.au