Crown rot and nematodes

GRDC code: DAN00175, National crown rot epidemiology and management program

Are you growing the right variety?

Plant Breeders Rights symbolVarieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.

Steven Simpfendorfer and Matt Gardner, NSW DPI, TamworthGreg Brooke and Leigh Jenkins, NSW DPI, Trangie

Take home messages

  • Two durum and 10 bread wheat varieties were evaluated in the presence of added or no added crown inoculum across 11 field sites in 2013.
  • Under high crown rot pressure (added CR inoculum) SuntopProtected under the Plant Breeders Rights Act 1994 was 0.42 t/ha, LRPB LancerProtected under the Plant Breeders Rights Act 1994 0.51 t/ha, SunguardProtected under the Plant Breeders Rights Act 1994 0.61 t/ha and LRPB SpitfireProtected under the Plant Breeders Rights Act 1994 0.63 t/ha higher yielding than EGA GregoryProtected under the Plant Breeders Rights Act 1994 on average across sites.
  • Where no additional CR was added EGA GregoryProtected under the Plant Breeders Rights Act 1994 had similar yield to other varieties at sites with low background levels of crown rot but was between -0.52 t/ha (SuntopProtected under the Plant Breeders Rights Act 1994) to -0.37 t/ha (SunguardProtected under the Plant Breeders Rights Act 1994) lower yielding at sites with medium-high background levels of crown rot.
  • EGA GregoryProtected under the Plant Breeders Rights Act 1994 production should be specifically targeted to paddocks with lower levels of crown rot risk based on testing such as PreDicta B.
  • Some newer wheat varieties have a measurable improvement in their tolerance to crown rot but these current levels are not a complete solution to crown rot. The best varieties still suffered up to 34% and 41% yield loss at the two sites with the highest impact from crown rot infection.

Introduction

Crown rot, caused predominantly by the fungus Fusarium pseudograminearum (Fp) is a significant disease of winter cereals in the northern region. Root lesion nematodes (RLNs) are also a wide spread constraint to wheat production across the region. Two important species of RLN exist throughout the northern region, namely Pratylenchus thornei (Pt) and P. neglectus (Pn). Previous surveys of the northern NSW have found that Pt is more widespread and generally at higher populations than Pn. Recent collaborative research between Northern Grower Alliance and NSW DPI has also established that the presence of RLN feeding within root systems increases the severity of crown rot.

Cereal varieties differ in their tolerance to crown rot and either species of RLN. This can have a significant impact on the relative yield of varieties in the presence of these various disease constraints. In 2013, NSW DPI conducted a series of 11 trials across central/northern NSW extending into southern Qld to examine the impact of crown rot and RLN on the yield of two durum and ten bread wheat varieties.

What did we do?

Eleven trials were sown between the 15 May and the 4 July in 2013. The six ranges at each site were soil cored separately at sowing to establish background levels of crown rot and RLN using PreDicta B (Table 1). Two durum and 10 bread wheat varieties (Table 2) were established at each site with the sowing rate adjusted to target 100 plants/m2 based on seed weight and germination. LRPB CrusaderProtected under the Plant Breeders Rights Act 1994 and SUN663A were not included in the Garah and Rowena trials. Each variety had either added or no added crown rot (CR) inoculum as durum grain colonised by Fp in the seed furrow at sowing. The only site where frost damage was noted in 2013 was with the quicker maturing varieties LRPB DartProtected under the Plant Breeders Rights Act 1994 and JandaroiProtected under the Plant Breeders Rights Act 1994 at Coonamble.

What did we find?

The average yield of the 12 cereal varieties at each of the 11 trial sites in the presence of no added CR or added CR varied across the sites (Table 1). Tamworth was the only site where the addition of CR inoculum at sowing did not result in a significant reduction in yield. This was a function of moderate levels of CR inoculum already present across the site and comparatively low yields. Data is therefore presented as an average of the added CR and no added CR treatments for this site.

The impact of added CR on yield was highest at Rowena and Macalister with 53% and 57% yield loss, respectively and considerably lower at Spring Ridge (15%) and Trangie (14%) (Table 1). However, determining yield loss by comparing inoculated and uninoculated plots across sites potentially underestimates the full impact of crown rot on yield at some sites. PreDicta B coring at sowing indicated that 6 of the 11 sites had medium to high levels of CR inoculum already present across the trial area (Table 1). Comparisons would underestimate losses at these sites as there is no way to account for yield loss that is attributed to the background infection levels in the no added CR plots. Yield outcomes are also a function of the interaction of each variety with CR, RLN populations which varied across the sites (Table 1), starting soil water, in-crop rainfall and maturity relative to moisture/temperature stress during the flowering and grain-fill period. 

Table 1. Field sites, sowing dates, background risk levels of root lesion nematodes (RLN) and crown rot at sowing and average site yield without and with added crown rot inoculum in 2013
Site
Sowing Date
Background levels
Av. site mean yield (t/ha)
RLN
Crown rot
No added CR
Added CR
Bithramere
7 June
Medium Pn
High
2.25
1.88
Tamworth
4 July
Nil
Medium
1.39
1.39
Spring Ridge
23 June
Nil
Medium
5.03
4.29
Terry Hie Hie
29 May
Nil
Low
3.69
2.95
Narrabri
17 May
Medium Pt
Medium
3.21
2.68
Coonamble
15 May
Nil
Medium
4.59
3.54
 Trangie  28 May
 Low Pn
 Nil  3.62  3.12
 Rowena  30 May
 Low Pt
 Nil  3.29  1.55
 Garah  31 May
 Low Pt
 Low  2.62  2.03
 Macalister  5 June
 Low Pt
 Low  3.35  1.43
 Westmar  31 May
 Nil  Medium  2.26 1.89

The average yield loss (difference between no added CR and added CR treatments) across the 11 sites was roughly in line with the reported crown rot resistance ratings (Table 2). The very susceptible and susceptible varieties averaged between 30-39% yield loss while the moderately resistant-moderately susceptible variety SunguardProtected under the Plant Breeders Rights Act 1994 had roughly half the level of yield loss (17%).

LRPB SpitfireProtected under the Plant Breeders Rights Act 1994 and QT14381, which are both MS, averaged the same level of yield loss as SunguardProtected under the Plant Breeders Rights Act 1994 even though they have a lower resistance rating. SuntopProtected under the Plant Breeders Rights Act 1994 which is also rated MS to crown rot averaged a higher level of yield loss (25%) than the other MS rated varieties. As outlined earlier these numbers are likely to be an underestimate of the impact of crown rot due to background inoculum levels at over half of the sites. Comparing varieties in terms of percentage yield loss can also be potentially misleading for growers and advisers as it masks the actual yields obtained in the presence of crown rot.  

Table 2. Crown rot resistance, Pratylenchus thornei (Pt) tolerance and P. neglectus (Pn) rating of 12 cereal varieties across 11 sites in 2013 and relative yield loss from the addition of CR inoculum. *indicates provisional rating
 Variety Crown rot
Pt tolerance
Pn tolerance
Av. % yield loss
Caparoi
VS
MI
MI-I
39
Jandaroi
VS
MI-I
MI
30
EGA Gregory
S
MT
MI
30
Strzelecki
S
I-VI
MI
30
Suntop
MS
MT
MI*
25
LRPB Dart
MS-S
MI
MI-I*
23
SUN663A
MS-S*
MT*
-
23
LRPB Lancer
MS-S*
MT-MI*
-
21
LRPB Crusader
MS-S
MI-I
MI-I
19
LRPB Spitfire
MS
MT-MI
MI
17
QT14381
MS*
MT*
-
17
Sunguard
MR-MS
MT
MI
17

Under high crown rot pressure (added CR) only the two durum varieties (CaparoiProtected under the Plant Breeders Rights Act 1994 and JandaroiProtected under the Plant Breeders Rights Act 1994) and the bread wheat variety StrzeleckiProtected under the Plant Breeders Rights Act 1994 were lower yielding than EGA GregoryProtected under the Plant Breeders Rights Act 1994 when averaged across sites (Table 3). The remaining bread wheat varieties all appear to have improved tolerance to crown rot compared to EGA GregoryProtected under the Plant Breeders Rights Act 1994 with yield benefits in added CR treatments of between +0.26 t/ha (LRPB DartProtected under the Plant Breeders Rights Act 1994) up to +0.63 t/ha (LRPB SpitfireProtected under the Plant Breeders Rights Act 1994).

Table 3. Average yield (t/ha) of varieties with no added CR and added CR at sowing, protein level obtained and yield difference (%) compared with EGA GregoryPBR logo in no added CR plots at sites with either nil to low or medium to high background levels of crown rot
Variety Av. site yield (t/ha) Protein Yield (% EGA Gregory)
No added CR Add CR Nil/Low CR Med/high CR
Caparoi 2.72 1.66 13.4 85 86
Jandaroi 2.63 1.83 14.2 82 84
EGA Gregory 3.81 2.21 12.2 100 100
Strzelecki 2.97 2.08 12.7 92 95
Suntop 3.49 2.63 12.5 102 117
LRPB Dart 3.19 2.47 12.9 94 106
SUN663A 3.41 2.64 12.9 103 113
LRPB Lancer 3.43 2.72 13.5 101 115
LRPB Crusader 3.41 2.78 13.1 108 110
LRPB Spitfire 3.42 2.84 13.9 100 115
QT14381 3.42 2.83 12.3 103 112
Sunguard 3.40 2.82 12.7 102 112

Under lower crown rot levels (no added CR) the two durum varieties and StrzeleckiProtected under the Plant Breeders Rights Act 1994 were again lower yielding than EGA GregoryProtected under the Plant Breeders Rights Act 1994, while LRPB Dart had an equivalent average yield across sites (Table 3). The remaining bread wheat varieties were between +0.22 t/ha (SunguardProtected under the Plant Breeders Rights Act 1994) to +0.31 t/ha (SuntopProtected under the Plant Breeders Rights Act 1994) higher yielding than EGA GregoryProtected under the Plant Breeders Rights Act 1994. This probably reflects the medium to high background crown rot levels in just over half of the sites and supports the improved crown rot tolerance of these newer varieties as evident in the added CR treatments.

Protein levels were fairly high across sites in 2013 ranging from a variety average of 11.9% (Spring Ridge) to 14.3% (Bithramere). JandaroiProtected under the Plant Breeders Rights Act 1994 had the highest protein concentration at 14.2% while EGA GregoryProtected under the Plant Breeders Rights Act 1994 averaged the lowest protein concentration at 12.2%. LRPB SpitfireProtected under the Plant Breeders Rights Act 1994 was the highest bread wheat variety at 13.9% which was 1.7% higher than that achieved by EGA GregoryProtected under the Plant Breeders Rights Act 1994 when averaged across sites (Table 3).

Further examining the relative yield of varieties compared to EGA GregoryProtected under the Plant Breeders Rights Act 1994 across the no added CR treatments highlights the value of determining the background levels of crown rot in trial sites (e.g. using PreDicta B). This treatment is essentially equivalent to GRDC funded National Variety Trial (NVT) sites with plots located in grower paddocks where both background crown rot and/or RLN levels may be present at varying levels. The Coonamble, Macalister and Westmar trials were actually co-located with cereal NVT sites in 2013. There were five sites with nil to low background levels of crown rot and six sites with medium to high starting levels (Table 1). SuntopProtected under the Plant Breeders Rights Act 1994, LRPB LancerProtected under the Plant Breeders Rights Act 1994, LRPB SpitfireProtected under the Plant Breeders Rights Act 1994 and SunguardProtected under the Plant Breeders Rights Act 1994 had similar yields to EGA GregoryProtected under the Plant Breeders Rights Act 1994 at sites with nil/low background levels of crown rot but were between 17% (SuntopProtected under the Plant Breeders Rights Act 1994) to 12% (SunguardProtected under the Plant Breeders Rights Act 1994) higher yielding than EGA GregoryProtected under the Plant Breeders Rights Act 1994 at sites with medium/high background levels of crown rot (Table 3). This highlights the potential impact that targeting the production of EGA GregoryProtected under the Plant Breeders Rights Act 1994 specifically to paddocks with lower levels of crown rot risk based on PreDicta B testing could have on the profitability of growing this popular variety. Growers and advisors should also take into account the background levels at trial sites, if known, before interpreting their local NVT results.

Determining the relative impact of crown rot versus RLN on yield from these current trials is difficult as the varieties with reduced tolerance to Pt (CaparoiProtected under the Plant Breeders Rights Act 1994, JandaroiProtected under the Plant Breeders Rights Act 1994, StrzeleckiProtected under the Plant Breeders Rights Act 1994, LRPB DartProtected under the Plant Breeders Rights Act 1994 and LRPB CrusaderProtected under the Plant Breeders Rights Act 1994) also have lower resistance to crown. The varieties also do not vary greatly in their tolerance to Pn. Furthermore, only two sites had medium levels of RLN with Bithramere having Pn and Narrabri Pt. The remaining sites had low or no RLN populations which limits the ability to infer nematode impacts. However, Narrabri in 2013 which had medium risk of both Pt and crown rot highlights the benefit of growing varieties with improved tolerance to Pt (e.g EGA Gregory 3.09 t/ha) or combined tolerance to Pt and resistance to crown rot (e.g. Suntop 3.87 t/ha) compared to varieties with poor levels of resistance/tolerance to both pathogens (e.g. Strzelecki 2.45 t/ha).

Conclusions

Determining the relative tolerance of varieties to crown rot is complex as it can be significantly influenced by background inoculum levels, RLN populations, differential variety tolerance to Pn versus Pt and varietal interaction with the expression of crown rot. Other soil-borne pathogens such as Bipolaris sorokiniana, which causes common root rot, also need to be accounted for in the interaction between crown rot and varieties. Starting soil water, in-crop rainfall, relative biomass production, sowing date and resulting variety phenology in respect to moisture and/or temperature stress during grain-fill can all differentially influence the expression of crown rot in different varieties. The research reported above needs to be conducted over a number of seasons and locations with full measurement of these influencing factors to fully understand the relative tolerance of varieties to crown rot under varying conditions. A more detailed interpretation of individual site results will be available in the autumn 2014 Northern Grains Region Trial Results book, published annually by NSW DPI.

Summary

The 2013 season was very conducive to the expression of crown rot in the northern region with little rainfall in spring and hot grain-fill temperatures. EGA GregoryProtected under the Plant Breeders Rights Act 1994 remains the dominant wheat variety across the region due to its high yield potential and flexibility in sowing time. However, under high crown rot pressure (i.e. added CR treatments) SuntopProtected under the Plant Breeders Rights Act 1994 was 0.42 t/ha, LRPB LancerProtected under the Plant Breeders Rights Act 1994 0.51 t/ha, SunguardProtected under the Plant Breeders Rights Act 1994 0.61 t/ha and LRPB SpitfireProtected under the Plant Breeders Rights Act 1994 0.63 t/ha higher yielding than EGA GregoryProtected under the Plant Breeders Rights Act 1994 when averaged across the 11 sites in 2013. This reflects the improved levels of tolerance to crown rot and Pt in recently released varieties in the region, which can significantly impact on profitability in the presence of these disease constraints.

Due to its increased susceptibility to crown rot growers should consider targeting EGA GregoryProtected under the Plant Breeders Rights Act 1994 production to paddocks with low risk of crown rot development based on testing such as PreDicta B. Otherwise growers should consider switching to one of these newer varieties, which have a measurable yield improvement in the presence of crown rot. Growers still need to be aware that significant yield loss can occur in these more tolerant varieties under high infection levels, particularly when plants suffer serious moisture/temperature stressed during grain-fill. Macalister and Rowena were sites that experienced the greatest yield loss from crown rot in 2013. Under high infection levels the best variety at Macalister was LRPB SpitfireProtected under the Plant Breeders Rights Act 1994 which still suffered 34% yield loss while SunguardProtected under the Plant Breeders Rights Act 1994 was the best at Rowena but still suffered 41% yield loss from crown rot. That is, some of these newer varieties have a measurable improvement in their tolerance to crown rot but these current levels are still not a complete solution to crown rot.

Acknowledgments

This project was co-funded by NSW DPI and GRDC under the national crown rot epidemiology and management project (DAN00175). Technical assistance provided by Robyn Shapland, Finn Fensbo, Karen Cassin, Kay Warren, Jim Keir, Rod Bambach, Peter Formann, Stephen Morphett and Jim Perfrement all based with NSW DPI at Tamworth are gratefully acknowledged. The technical assistance of Jayne Jenkins with NSW DPI based at Trangie is also appreciated. The two southern Qld sites (Westmar and Macalister) were kindly managed by Douglas Lush (QDAFF).

Contact details

Dr Steven Simpfendorfer

NSW DPI

Ph: 0439 581 672

Email: steven.simpfendorfer@dpi.nsw.gov.au

GRDC Project code: DAN00175