SYMPTOMS AND DETECTION | VARIETAL RESISTANCE OR TOLERANCE |
MANAGEMENT OF NEMATODES | TESTING FOR ROOT-LESION NEMATODES
WESTERN
SEPTEMBER 2018
SECTION 8
NEMATODE MANAGEMENT
BARLEY
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Nematode management
Root-lesion nemtodes (RLN; Pratylenchus spp.) are microscopic, worm-like animals
that extract nutrients from plants, causing yield loss. 1
Root-lesion nematodes are found over 5.74 million hectares (or ~65%) of the
cropping area of WA and populations potentially limit yield in at least 40% of these
infested paddocks.
The host range of RLN is broad and includes cereals, oilseeds, grain legumes and
pastures, as well as many broadleaf and grass weeds.
The main species found in broadacre cropping in WA are Pratylenchus neglectus, P.
quasitereoides (originally described as P. teres), P. thornei and P. penetrans.
Which nematode species are present will affect the suitability of the rotational options.
Barley in the Western Region is considered susceptible to P. neglectus, susceptible to
P. quasitereoides and moderately susceptible to P. penetrans. 2
table 1: Resistance of major crop broadacre species to Pratylenchus neglectus, P.
quasitereoides and P. penetrans
Susceptible Moderately susceptible Resistant
P. neglectus
Wheat Canola Field peas
Barley Oats Lupins
Chickpeas Durum wheat Faba beans
Lentils
Triticale
Rye
Safflower
Narbon beans
P. quasitereoides (formerly P. teres)
Wheat Canola Field peas
Barley Lupins
Oats
P. penetrans
Field peas Barley
Lupins Canola
Chickpeas
Oats
Durum wheat
Wheat
Triticale
Faba beans
Wild oats
Wild radish
Souce: Soil Quality Background
1 KJ Owen, J Sheedy, N Seymour (2013) Root lesion nematode in Queensland. Soil Quality Pty Ltd. Fact sheet, http://www.soilquality.org.
au/factsheets/root-lesion-nematode-in-queensland
2 GRDC (2015) Tips and Tactics: Root-Lesion Nematodes, Western Region, Fact sheet, http://www.grdc.com.au/TT-RootLesionNematodes
i MORE INFORMATION
GrdC (2015) tip and tactics: root-
Lesion nematodes. Fact sheet.
Know more. Grow more.
Management of root-lesion nematodes in
winter crops
• Observation and monitoring of above and below ground symptoms
of plant disease, followed by diagnosis of the cause(s) of any root
disease, is the first step in implementing effective management.
Although little can be done during the current cropping season to
ameliorate nematode symptoms, the information will be crucial in
planning effective rotations of crop species and varieties in following
seasons.
• Well-managed rotations with resistant or non-host break-crops are
vital. To limit RLN populations, avoid consecutive host crops (Table 1).
• Use a state department of agriculture Crop Variety Guide to choose
varieties with high resistance ratings, which result in fewer nematodes
remaining in the soil to infect subsequent crops.
• Reducing RLN can lead to higher yields in following cereal crops.
• Healthy soils and good nutrition can partly alleviate RLN damage
through good crop establishment, and healthier plants may recover
more readily from infestation under more suitable growing conditions.
• Observe crop roots to monitor development of symptoms.
• Weeds can host parasitic nematodes within and between cropping
sequences, so choice of pasture species and control of host weed
species and crop volunteers is important (Table 2).
Root-lesion nematodes (RLN; Pratylenchus species) are significant pests that feed on the roots of
crop plants and cause yield loss.
KEY POINTS
• Root-lesion nematodes are found over 5.74 million ha (or ~65%) of the cropping area of Western Australia (WA). Populations potentially limit
yield in at least 40% of these infested paddocks.
• The main species found in broadacre cropping in WA are Pratylenchus neglectus, P. quasitereoides (formerly known as P. teres), P. thornei
and P. penetrans.
• The host range of RLN is broad and includes cereals, oilseeds, grain legumes and pastures, as well as many broadleaf and grass weeds.
• Nematode species present will influence the choice of suitable rotational options.
FEBRUARY 2015
About the root-lesion nematode
Pratylenchus are microscopic, worm-like organisms
less than 1 mm in length and cannot be seen
with the naked eye (Figure 1). They are migratory
endoparasites, meaning that they enter roots to feed
and lay eggs but may live for some time in soil, feeding
on the exterior of the roots or travelling between
roots and plants. All RLN species can survive dry
periods in a dehydrated form or as eggs within roots
or soil. Climatic and soil conditions are ideal for RLN
reproduction during the broadacre cropping season
in WA, and populations have the ability to increase
rapidly during a cropping season in susceptible crops.
Figure 1. Mature root-lesion nematode, less than 1
mm long, as viewed under the microscope and cannot
be seen. Notice the syringe-like stylet at the head end,
which is used to penetrate plant roots and extract
nutrients.
Tips and Tactics
ROOT-LESION NEMATODES
WESTERN REGION
http://www.soilquality.org.au/factsheets/root-lesion-nematode-in-queens…
http://www.soilquality.org.au/factsheets/root-lesion-nematode-in-queens…
http://www.grdc.com.au/TT-RootLesionNematodes
https://grdc.com.au/TT-RootLesionNematodes
https://grdc.com.au/TT-RootLesionNematodes
mailto:GrowNotes.West%40grdc.com.au?subject=
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Root-lesion nematodes use a syringe-like ‘stylet’ to extract nutrients from the roots
of plants (Photo 1). Plant roots are damaged as RLN feed and reproduce inside the
plant roots. Pratylenchus thornei and P. neglectus are the most common RLN species
in Australia. These nematodes can be found deep in the soil profile (to 90 cm depth)
and in a broad range of soil types, from heavy clays to sandy soils. 3
New CSIRO research funded by the GRDC is examining how nematodes inflict
damage by penetrating the outer layer of wheat roots and restricting their ability to
transport water.
Photo 1: Microscope image of a root-lesion nematode. Notice the syringe-like
‘stylet’ at the head end, which is used for extracting nutrients from the plant root.
This nematode is less than 1 mm long.
Source: Sean Kelly, DAFWA)
8.1 Symptoms and detection
Root-lesion nematodes are microscopic organisms that occur in soil and plants. The
most reliable way to confirm the presence of RLN is to have soil tested in a laboratory.
Signs of nematode infection in roots include dark lesions or poor root structure (Photo
2). The damaged roots are inefficient at taking up water and nutrients—particularly
nitrogen, phosphorus and zinc—causing symptoms of nutrient deficiency and wilting
in the plant shoots. Intolerant wheat varieties may appear stunted, with yellowing
of lower leaves and poor tillering. However, these symptoms may not be present in
other susceptible crops such as barley and chickpea. 4
What is seen in the paddock?
Above-ground symptoms are often indistinct and difficult to identify. The first signs
are poor establishment, stunting, poor tillering of cereals, and plants possibly wilting
despite moist soil. Nematodes are usually distributed unevenly across a paddock,
resulting in irregular crop growth. Sometimes symptoms are confused with nutrient
deficiency and they can be exacerbated by a lack of nutrients.
3 KJ Owen, J Sheedy, N Seymour (2013) Root lesion nematode in Queensland. Soil Quality Pty Ltd. Fact sheet, http://www.soilquality.org.
au/factsheets/root-lesion-nematode-in-queensland
4 KJ Owen, J Sheedy, N Seymour (2013) Root lesion nematode in Queensland. Soil Quality Pty Ltd. Fact sheet, http://www.soilquality.org.
au/factsheets/root-lesion-nematode-in-queensland
i MORE INFORMATION
dAFWA (2014) How to diagnose root
Lesion nematode. Video.
dAFWA (2014) Crop damaging
nematodes found in new area. Media
release.
s Collins et al. (2014) root lesion
nematode has a picnic in 2013. GrdC
update Papers.
s Collins et al. (2013) Pratylenchus
teres WA’s home grown root Lesion
nematode. GrdC update Papers.
GrdC (2010) Plant Parasitic
nematodes (southern & Western
region). Fact sheet.
http://www.soilquality.org.au/factsheets/root-lesion-nematode-in-queens…
http://www.soilquality.org.au/factsheets/root-lesion-nematode-in-queens…
http://www.soilquality.org.au/factsheets/root-lesion-nematode-in-queens…
http://www.soilquality.org.au/factsheets/root-lesion-nematode-in-queens…
http://www.youtube.com/watch?feature=player_detailpage&v=ttFltE-B4qA&li…
http://www.youtube.com/watch?feature=player_detailpage&v=ttFltE-B4qA&li…
https://www.agric.wa.gov.au/news/media-releases/crop-damaging-nematodes…
https://www.agric.wa.gov.au/news/media-releases/crop-damaging-nematodes…
https://www.agric.wa.gov.au/news/media-releases/crop-damaging-nematodes…
http://www.giwa.org.au/pdfs/2014/Presented_Papers/Collins%20Sarah_Root%…
http://www.giwa.org.au/pdfs/2014/Presented_Papers/Collins%20Sarah_Root%…
http://www.giwa.org.au/pdfs/2014/Presented_Papers/Collins%20Sarah_Root%…
https://grdc.com.au/Research-and-Development/GRDC-Update-Papers/2013/03…
https://grdc.com.au/Research-and-Development/GRDC-Update-Papers/2013/03…
https://grdc.com.au/Research-and-Development/GRDC-Update-Papers/2013/03…
https://grdc.com.au/Resources/Bookshop/2010/10/Plant-Parasitic-Nematode…
https://grdc.com.au/Resources/Bookshop/2010/10/Plant-Parasitic-Nematode…
https://grdc.com.au/Resources/Bookshop/2010/10/Plant-Parasitic-Nematode…
mailto:GrowNotes.West%40grdc.com.au?subject=
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Photo 2: Barley roots with symptoms of Pratylenchus damage including stunting,
lack of lateral roots, and browning lesions.
Source: GRDC
When roots are damaged by RLN (Photo 2), plants are less able to tolerate stresses
such as drought or nutrient deficiencies. Depending on the extent of damage and the
growing conditions, affected plants may partly recover if the rate of new root growth
exceeds the rate at which nematodes damage the roots.
Gaining the full picture requires an examination of what is going on under the
ground. Primary and secondary roots of cereals will show a general browning and
discoloration and there will be fewer, shorter laterals branching from the main roots.
The root cortex (or outer root layer) may be damaged and it may disintegrate.
Diagnosis is difficult and can be confirmed only with laboratory testing. This is
essential if identification is sought to species level as all RLN species cause identical
symptoms. The PreDicta B™ soil test (SARDI Diagnostic Services) is a useful tool for
several nematode species and is available through accredited agronomists. 5
RLN and acidic soil
Western Australia’s acidic soils could be exacerbating the impact of RLN and limiting
crop yields and growers’ profitability.
Initial research by DAFWA supported by the GRDC, has found significantly higher RLN
populations in barley, lupin and wheat crops grown in low pH soils.
The nematology research group at DAFWA conducted a series of glasshouse trials to
test the impact of soil acidity on the multiplication of the main RLN species that impact
WA wheat, barley and lupin crops.
The plants were grown in acidic soils (pH 5.1) taken from the same paddock and
compared with plants grown in soil that had been treated with lime (pH 6.7).
5 GRDC (2015) Tips and Tactics: Root-Lesion Nematodes, Western Region, Fact sheet, http://www.grdc.com.au/TT-RootLesionNematodes
http://www.grdc.com.au/TT-RootLesionNematodes
mailto:GrowNotes.West%40grdc.com.au?subject=
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Significantly higher final populations of P. quasitereoides were recorded for seven
of the nine wheat, barley and lupin varieties grown in low pH soil compared with the
same varieties grown in the same soil limed to moderate pH.
The same result was recorded in barley for P. neglectus.
Diagnostic and management information is available by downloading the free
MyCrop app for wheat, barley, canola and lupins. 6
The life cycle of RLN
Root-lesion nematodes are migratory plant parasitic nematodes, and will migrate
freely between roots and soil if the soil is moist. In WA, the life cycle of RLN begins
after the opening rains in autumn.
Juvenile and adult nematodes rehydrate, become active and invade plant roots,
where they feed and multiply as they move through the root (Figure 1). Individual eggs
are laid within the root, from which juvenile nematodes hatch and grow to adults,
which in turn lay more eggs. They develop from egg to adult in 40–45 days (~6
weeks) depending on soil temperature and host. There may be 3–5 life cycles within
the plant host each season.
As plants and soil dry out in late spring, RLN enter a dehydrated state called
anhydrobiosis and can survive high soil temperatures and desiccation over summer.
As the nematodes feed and multiply, lesions and/or sections of brown discoloration
are formed on the plant root. Other symptoms include reduction in the number and
size of lateral roots and root hairs. 7
Figure 1:
Nematodes rehydrate and
become active following rains
and invade growing plant roots
Nematode invades
the outer layers of
the root (cortex)
Stele
Nematode feeding
may cause cortical
tissue to turn
brown, collapse
and breakdown
Eggs laid
in roots
Eggs laid
in soil
Nematodes reproduce and
migrate within roots and soil
Stage 1 moults
within eggs
All stages
attack roots
There may be several
generations of nematodes
each growing season
Stage 2 larvae
Stage 3 larvae
Stage 4 larvae
Adult
All stages of
nematodes can
survive betweeen
crops within root
pieces or in a
desiccated state
Disease cycle of root-lesion nematode
adapted from: GN Agrios (1997) Plant pathology, 5th edn (Academic Press: New York). (Illustration by Kylie Fowler)
6 DAFWA (2015) Soil acidity could increase risk of Root Lesion Nematodes. Media release. Department of Agriculture and Food, Western
Australia, https://www.agric.wa.gov.au/news/media-releases/soil-acidity-could-incr…
7 GRDC (2015) Tips and Tactics: Root-Lesion Nematodes, Western Region, Fact sheet, http://www.grdc.com.au/TT-RootLesionNematodes
https://www.agric.wa.gov.au/mycrop
https://www.agric.wa.gov.au/news/media-releases/soil-acidity-could-incr…
http://www.grdc.com.au/TT-RootLesionNematodes
mailto:GrowNotes.West%40grdc.com.au?subject=
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P. quasitereoides
P. quasitereoides (originally described as P. teres) is unique to WA, and can reach
high populations and cause more significant and widespread damage within a crop
than P. neglectus. Growers need to manage P. quasitereoides within their cropping
rotations through the use of species which are poor or non-hosts, or use resistant
wheat and barley cultivars to limit the multiplication of this pest in the soil. Although
P. quasitereoides is not as widespread, crops resistant to P. neglectus can be highly
susceptible to this species, requiring a different suite of rotational crops and cultivars
for effective management. It is necessary that in field diagnoses, the species of RLN
is correctly identified to enable growers to choose appropriate crop cultivars and
species to minimise current and future losses. 8
Canola has been found to increase P. quasitereoides numbers especially if the
canola is grown after a long cereal phase.
Economic importance
In WA, all growing regions are affected by RLN (Figure 2) and at least 65% of cropping
paddocks are infested with one or more of the Pratylenchus species. Populations
potentially limit yield in at least 40% of these infested paddocks.
Yield losses in broadacre cropping caused by P. quasitereoides or P. penetrans are
a problem specific to WA. Research is under way to learn more about these species
and the rotations that will limit their population below damaging levels in cropping
soils. More than one RLN species can be found in the roots of an individual crop,
although one species usually dominates.
Figure 2: Positive detection of root-lesion nematodes in Western Australia’s
broadacre cropping region between 1997 and 2013.
Source: DAFWA
8 GRDC (2013) Pratylenchus teres WA’s home grown Root Lesion Nematode. GRDC Update Papers, 12 March 2013, https://grdc.com.au/
Research-and-Development/GRDC-Update-Papers/2013/03/Pratylenchus-teres-WAs-home-grown-Root-Lesion-Nematode
https://grdc.com.au/Research-and-Development/GRDC-Update-Papers/2013/03…
https://grdc.com.au/Research-and-Development/GRDC-Update-Papers/2013/03…
mailto:GrowNotes.West%40grdc.com.au?subject=
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DAFWA has conducted research for nearly 20 years into the distribution, host range
among crop species, variety resistance within crop species, and yield impacts
of RLN on crops, including research trials, surveys and Agwest Plant Laboratory
diagnostic samples.
During this time, 486 varieties across a wide range of crops have been assessed for
resistance to the four main RLN species. 9
Updated ratings
Recent studies sampling 765 paddocks in the 2014–15 seasons showed at least 50%
of infested paddocks had RLN at potentially yield limiting levels. P. neglectus was the
most frequent RLN, occurring in at least 63% of infested paddocks. P. quasitereoides
was the next most common RLN at around 26% of infected paddocks surveyed.
Cereal yield losses due to RLN are seasonally dependent and are in the order of
5–30%, but can be higher. RLN species P. neglectus and P. quasitereoides can cause
losses of up to 18% in barley crops.
The actual yield loss due to RLN in different barley varieties is not yet quantified, but
the impact of different varieties on nematode populations varies. The P. neglectus
and P. quasitereoides nematode resistance scores have been updated since the
last sowing guide to reflect WA only based observations. The ratings are based on
glasshouse trials 2009–14 for both RLN species plus field trials in 2014–15 for P.
quasitereoides (3 trials) and 2015 for P. neglectus (3 trials). 10
8.2 Varietal resistance or tolerance
Resistance and susceptibility of crops can differ for each RLN species. A resistant
crop does not allow RLN to reproduce and increase in number (the opposite is
susceptibility). 11 Tolerant varieties grow and yield well when RLN are present.
For example, field peas, lupins and faba beans are resistant to P. neglectus but
susceptible to P. penetrans; barley may be more susceptible to P. quasitereoides than
to P. neglectus; and canola is more susceptible to P. neglectus than to P. thornei.
Although there is no truly resistant variety of wheat, barley or oats, sufficient variation
exists for susceptibility that variety selection in rotations can be a useful tool in
managing the impact of RLN.
Pastures vary in their susceptibility to RLN, and under some pasture species,
nematode levels could increase and become damaging to subsequent cereals.
Pastures
