Is sowing time, row spacing or plant population a viable management tool to minimise losses from crown rot?

Matthew Gardner and Steven Simpfendorfer, NSW DPI Tamworth

Background

Crown rot caused by the fungus Fusarium pseudograminearum is a major constraint to winter cereal production in the northern grains region. Yield losses attributed to crown rot can be in excess of 70% in very susceptible crops such as durum and where moisture stress is present during grain fill. Unfortunately for the industry there does not appear to be a genetic or agronomic “silver bullet” that will negate the losses associated with crown rot or eliminate the build-up of inoculum within the system. Therefore, adapting our current practices and varieties to focus on managing the three key phases of crown rot (survival, infection and yield loss) will determine the impact this disease has on your crops in the future.

The crown rot fungus survives on cereal and grass weed residues, while infection occurs throughout the season and requires direct contact with infected residues.  Yield loss is related to moisture stress post anthesis. Moisture stress is suspected to cause the crown rot fungus to proliferate in the base of infected tillers, restricting water movement from the roots through the stems, and producing whiteheads that contain either no grain or lightweight shrivelled grain.

Some practices to manage the survival and infection phases of crown rot are discussed elsewhere in the proceedings. This paper is focused on the potential of sowing time and row spacing to reduce the level of moisture stress post anthesis and hence minimise the extent of yield loss from crown rot. It was hypothesised that the early time of sowing allows grain fill to occur under cooler conditions, whereas, wider row spacing’s may provide the capacity to conserve moisture for later in the season and reduce moisture stress during grain fill.

What did we do?

In 2012 there were two crown rot trials conducted, one involved time of sowing (TOS) and the other was a row spacing trial. Both were conducted on the property ‘Wattle Plains’ near Walgett in north-west NSW. PreDicta B soil cores were taken prior to sowing which measured 1700 Pratylenchus thornei/kg soil (0-30 cm), which is just below the indicative threshold for yield loss in intolerant varieties.

In the TOS trial there were 18 different varieties (10 bread wheat, 4 barley and 4 durum varieties listed in figure 1) planted on the 30^th April and the 28^th May. A plus or minus crown rot treatment for each variety was implemented where the plus treatment had durum seed colonised by five different isolates of Fusarium pseudograminearum sown with the plot seed at 50 kg/ha. The plot seed and inoculated seed were thoroughly mixed prior to sowing to ensure even infection across the plots.

The row spacing trial, planted on the 28^th May, included one durum variety (Caparoi), a barley variety (Commander) and a bread wheat (LongReach Spitfire) planted at 80 or 160 plants/m² across 300, 400 and 500 mm row spacing’s. For each treatment there was also a plus and minus crown rot treatment that was implemented using the same method as described for the TOS trial. Shortly after planting, all plots in the row spacing trial had a neutron probe access tube installed to 1.80 m depth to measure soil water content under the various treatments throughout the season. In addition, a wet up and rain out shelter were established at the same time to determine field capacity and wilting point for the site, respectively. Moisture contents were determined approximately every 21 days between stem elongation and physical maturity for the 0-30, 30-60, 60-90, 90-120, 120-150 and 150-180 cm depth intervals.  

All trials received 60 kg/ha of Granulock® supreme Z and 70 kg/ha of granulated urea at planting. Plant establishment was recorded approximately 20 days after sowing, while dry matter assessments were made at approximately stem elongation, anthesis and maturity. In addition, tiller and head counts were also conducted at maturity. Plot yields were determined using a plot harvester with both sowing times harvested on the 4^th November. In the row spacing trial the two outside rows of the plot were removed prior to harvest to reduce edge effects.  Unfortunately at the time of writing this paper, grain quality data was not available.  

What did we find?

Time of sowing (TOS)

The yield of bread wheats and barley infected by crown rot were not affected by TOS at Walgett in 2012. However, in durum the addition of crown rot inoculum resulted in a significant 12 % and 25% yield reduction from TOS 1 and 2, respectively. The negative yield impact associated with infection was significantly greater for TOS 2 than TOS 1, which suggests that the earlier planting time enabled some of the yield loss from crown rot to be negated in the durum varieties.   

Although it was expected that TOS 1 would have yielded better than TOS 2, there was no significant difference. This may be explained by differences in plant establishment with TOS 1 establishing an average of 26 plants/m² compared to TOS 2 that established an average of 102 plants/m², which was the target population (100 plants/m²). The poorer establishment of TOS 1 was a direct result of suboptimal sowing moisture but clearly the 4 week earlier sowing time allowed compensation for the 75% reduction in plant population compared to TOS 2.

There was a significant interaction between variety and the impact of crown rot (Figure 1). Yield losses were greatest for the durum varieties, ranging from 14% for Hyperno to 31% for EGA Bellaroi, whereas significant yield losses in the bread wheats ranged from 7% for Sunguard to 15% for EGA Wylie (Figure 1). Wimmera was the only barley variety to significantly lose yield from crown rot infection with a 0.32 t/ha loss (Figure 1). The average yields for barley, wheat and durum in the absence of crown rot was 5.9, 4.4 and 4.0 t/ha. The fact that bread wheat and durum yields were similar in the absence of crown rot inoculum suggests that background crown rot levels in the paddock did not confound the results. This will be confirmed through pathology assessment of stubble samples collected from the Walgett trial site after harvest. 

Figure 1: The effect of plus or minus crown rot inoculum on yield of 18 different varieties averaged across two sowing times at Walgett in 2012. Varieties designated with a star represent a significant yield loss from crown rot infection.

Yield achievement in the presence of crown rot (Figure 2) is perhaps a more useful means of comparing varieties rather than the extent of yield loss associated with infection (Figure 1) as a variety with the smallest yield loss may not always be the highest yield achiever. Although all durum varieties are susceptible to crown rot there were significant differences in yields between varieties. Hyperno was the highest yielding durum variety in the presence of crown rot with a yield similar to that of the bread wheats Sunvex, EGA Wylie, EGA Gregory, SUN643A and LongReach Spitfire (Figure 2). EGA Bellaroi and Jandaroi had yields 1.4 and 0.9 t/ha lower than Hyperno.  The quicker bread wheats, LongReach Dart, LongReach Spitfire and SUN643A, which had negligible losses to crown rot (Figure 1), had lower yields than both Suntop and Sunguard (Figure 2). Selecting Strezlecki or EGA Gregory over Sunguard in 2012 at the trial site cost 0.8 or 0.5 t/ha in yield where crown rot infection was present. Similarly growing Commander as opposed to Grout increased yields from 5.5 to 6.2 t/ha (Figure 2). These examples highlight that far greater gains in grain yield can be made by selecting the correct variety than having complete tolerance to crown rot.

Figure 2: The yield performance of 18 different varieties inoculated with crown rot averaged across two sowing times at Walgett in 2012. Bars designated with different letters indicates a significant difference between treatments (P=0.05).

Row Spacing

Commander had the highest yield whereas Caparoi had the lowest yield across all row spacing’s Caparoi was the only variety that experienced a significant yield reduction shifting from 300 to 400 mm row spacing, while all varieties had a yield reduction between the 400 mm and 500 mm row spacing (Figure 3a).  The presence of crown rot did not cause a yield reduction in Commander or LongReach Spitfire at any of the row spacing’s (data not shown). In contrast, yield loss associated with crown rot infection in Caparoi were 15, 22 and 23% at the 300, 400 and 500 mm row spacing’s, respectively (Figure 3b).

 

Figure 3: The effect of 300, 400 and 500 mm row spacing’s on the grain yield of Caparoi, Commander and LongReach Spitfire (a) and  the impact of plus or minus crown rot on the yield of Caparoi at the 300, 400 and 500 mm row spacing’s (b) at Walgett in 2012.

Row spacing had a significant impact on plant available water content (PAWC) in the surface 60 cm over the season, with 500 mm having lower PAWC compared to the other two row spacing’s (Figure 4a).  On average the 500 mm row spacing used an additional 14 mm of soil water between stem elongation to maturity. Below 60 cm there was no difference in PAWC between row spacing treatments.  There was also a significant affect of plant population with the 160 plants/m² using significantly more water over the season compared to the 80 plants/m² to a depth of 120 cm (Figure 4b), despite there being no significant difference in final grain yield. 

Figure 4: The effect of 300, 400 and 500 mm row spacing’s (a) and plant populations 80 and 160 plants/m2 (b) on plant available water content (PAWC) from stem elongation to maturity at Walgett in 2012. Bars represent Lsd (P=0.05).

LongReach Spitfire left significantly more soil water in the profile compared to both Caparoi and Commander at crop maturity, particularly in the surface 90 cm. Commander dried the soil profile to the greatest degree but was similar to Caparoi in the surface 90 cm. Caparoi and LongReach Spitfire used similar quantities of water from the 90 to 150 cm depth intervals (Figure 5a). The WUE of Caparoi, Commander and LongReach Spitfire equated to 14.2, 21.4 and 17.9 kg grain/mm water, respectively. The final measurement of soil water at crop maturity was the only sampling time where crown rot had a significant impact on PAWC. Less water was used between the 60 and 120 cm depth interval where plots were inoculated with crown rot (Figure 5b).

Figure 5: The effect of variety (a) and the presence of crown rot (b) on plant available water content (PAWC) at physical maturity of the crop on the 27 October at Walgett in 2012. Bars represent Lsd (P=0.05).

What are the conclusions?

TOS 1 achieved the same yield as TOS 2 with approximately 25% of the plant establishment, which highlights the potential for early planting and low populations to be used in the western environment. This has also been shown in previous NSW DPI trials across different seasons and sites. In durum the yield loss caused by crown rot was approximately half for TOS 1 (12%) compared to TOS 2 (25%). Despite being planted four weeks apart TOS 1 only flowered 5-10 days earlier than TOS 2 and matured at the same time, which is consistent with other studies where low plant populations have been shown to delay development. Given the similar development for both sowing times it is likely that the low plant population has had a large influence on reducing yield loss from crown rot infection observed with TOS 1. Results from the row spacing trial show that the 80 plants/m² used significantly less soil water than 160 plants/m² to a depth of 120 cm. Therefore, it would be expected in TOS 1, which had 25% of the plant population of TOS 2, there would have also been less soil water used throughout the season which may have reduced the moisture stress during grain fill and consequently yield loss from crown rot.

Yield losses to crown rot in the TOS trial and the row spacing trial were, not surprisingly, greatest for durum (15-30%), while only minimal for wheat (7-15%) and barley (<5%), which suggests that it wasn’t a disastrous crown rot year in 2012 at this site. This is primarily due to a full profile of moisture at the start of the season, with approximately 240 mm PAWC and average rainfall early in the season. If the stored moisture was lower, which is a likely scenario in 2013, yield losses would have been expected to be much more severe given the crown rot infection levels. Regardless these trials reinforce the need to avoid growing durum where there is a risk of crown rot.

It is important to determine a varieties performance under crown rot pressure and not necessarily just on relative yield loss to infection. Sunguard, which did have a significant 7% yield loss from crown rot infection, and Suntop yielded highest of the bread wheats in the presence of crown rot, while the quick varieties (LongReach Dart, LongReach Spitfire and SUN643A) generally had no significant yield loss from crown rot infection but were lower yielding in the presence of this disease.

It was hypothesised that increasing row spacing would conserve moisture in the profile for late in the season, which would reduce the yield loss from crown rot. However, the results suggest the opposite, with the 500 mm row spacing consistently having less PAWC in the surface 60 cm throughout the season. Yield loss to crown rot at the 500 mm row spacing was 12% worse than the 300 mm row spacing. It is not fully understood why there was greater water use for the 500 mm row spacing, but potentially there were greater evaporation losses as crop row closure was never achieved, particularly for Caparoi and LongReach Spitfire. This requires further investigation. Interestingly, there was no yield penalty for shifting from a 300 to 400 mm row spacing in barley (Commander) or the bread wheat (LongReach Spitfire), consistent with previous research in this environment. However, increasing yield loss was associated with each widening of the row spacing in the durum wheat (Caparoi). The agronomy of durum production has not been extensively evaluated in such a western environment due to limited commercial production in the region primarily based around concerns over the high susceptibility of this crop to crown rot. However, this research indicates that agronomy in this environment could potentially be different to that normally used for bread wheat and barley production. Encouragingly, the durum variety Hyperno also produced yield in the presence of crown rot equivalent to some of the bread wheat varieties indicating that further research into adapting durum production in this environment is warranted. 

Surprisingly crown rot significantly reduced soil water use during the three weeks prior to maturity in the 60 – 120 cm depth interval, which supports that the crown rot fungus proliferates in the base of infected tillers, restricting water movement from the roots through the stems at the onset of moisture stress. This again highlights that if the starting soil water was lower than at sowing in 2012, then the moisture stress would have been initiated well before the final three weeks of crop development with greater negative impacts from crown rot infection on yield likely. Furthermore, it will be important to determine the impact of this lower water use and disease interactions on grain quality.

Acknowledgments

The authors would like to thank Dave Denyer, “Wattle Plains” Walgett for providing the trial site. Technical assistance provided by Rod Bambach, Jan Hoskins, Patrick Mortell, Stephen Morphett, Ben Frazer and Jim Perfrement are gratefully acknowledged.

Contact details

Matthew Gardner
NSW Department of Primary Industries
Ph: 02 6763 1138
Fx: 02 6761 2222
Email: matthew.gardner@dpi.nsw.gov.au

Reviewed by

Guy McMullen