Root Lesion Nematode – Queensland

Key Points

• Root lesion nematodes (Pratylenchus spp.) are microscopic worm-like animals that extract nutrients from plants, causing yield loss.


• In the northern grain region, the root-lesion nematodes are found in three-quarters of fields tested – Pratylenchus thornei predominates but P. neglectus is also found.


• Intolerant crops such as wheat and chickpea can lose 20 – 50 % in yield when nematode populations are high.


• Resistance and susceptibility of crops can differ for each root-lesion nematode species, for example sorghum is resistant to P. thornei but susceptible to P. neglectus.


• Successful management relies on:
  
  
  
  • farm hygiene to keep fields free of root-lesion nematode.
  
  
  • growing tolerant varieties when root-lesion nematodes are present, to maximise yields.
  
  
  • rotating with resistant crops to keep root-lesion nematodes at low levels.
  
  
  
  

 

Background

Root lesion nematodes (RLN) are microscopic worm-like animals that use a syringe-like ‘stylet’ to extract nutrients from the roots of plants (figure 1). Plant roots are damaged as RLN feed and reproduce inside plant roots. Pratylenchus thornei and P. neglectus are the most common RLN species in Australia. In the northern grain region P. thornei is the predominant RLN but P. neglectus is also present. These nematodes can be found deep in the soil profile (to 90 cm depth) and are found in a broad range of soil types – from heavy clays to sandy soils.

 

Symptoms and detection

Root-lesion nematodes are microscopic and can’t be seen with the naked-eye in the soil or in plants. The most reliable way to confirm the presence of root-lesion nematodes is to have soil tested in a laboratory. Fee-for-service testing of soil by scientists at the Queensland Department of Agriculture, Fisheries and Forestry, (DAFF) (Test your farm for nematodes) or by Predicta-B^TM root disease testing service determines levels of P. thornei and P. neglectus present.

Signs of nematode infection in roots include dark lesions or poor root structure. 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 tops. Intolerant wheat varieties may appear stunted, with lower leaf yellowing and poor tillering (figure 2). These symptoms may not be present in other susceptible crops such as barley and chickpea.

Figure 1: Microscope image of a 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. (Photo: Sean Kelly, Department of Agriculture and Food, Western Australia).

 

Management

There are four key strategies for the management of root lesion nematodes:

1. Have soil tested for nematodes in a laboratory.


2. Protect paddocks that are free of nematodes by controlling soil and water run-off and cleaning machinery; plant nematode-free paddocks first.


3. Choose tolerant wheat varieties to maximise yields (go to nvtonline.com.au). Tolerant varieties grow and yield well when RLN are present.


4. Rotate with resistant crops to prevent increases in root-lesion nematodes (table 1, figure 3). When high populations of RLN are detected you may need to grow at least two resistant crops consecutively to decrease populations. In addition, ensure that fertiliser is applied at the recommended rate to ensure that the yield potential of tolerant varieties is achieved.

Figure 2: Symptoms of RLN infection of an intolerant wheat variety include lower leaf yellowing, decreased tillers and wilting. There are no obvious symptoms in the susceptible chickpea and faba bean plots on either side of the wheat. (Photo: Kirsty Owen, DAFF).

 

 

Table 1: Susceptibility and resistance of various crops to root lesion nematodes.

RLN Species
Susceptible
Intermediate
Resistant


P. thornei
wheat, chickpea, faba bean, barley, mungbean, navy bean, soybean, cowpea
Canola, mustard, triticale. Durum wheat, maize, sunflower
Canary seed, lab lab, linseed, oats, sorgum, millet, cotton, pigeon pea


P. neglectus
wheat, canola,chickpea, mustard, sorghum-grain, sorghum-forage
Barley, oat, canaryseed, durum wheat, maize, navy bean
Linseed, field pea, faba bean, triticale, mungbean, soybean

 

 

..

Figure 3: Crop rotation to manage root-lesion nematodes depends on the RLN species present in your field. Mungbeans (right) are susceptible to the root-lesion nematode P. thornei but are resistant to P. neglectus. In contrast, sorghum (far right) is resistant to P. thornei but susceptible to P. neglectus. (Photo: Kirsty Owen, DAFF)

 

Further reading and references

DEEDI, (2009) Root-lesion nematodes: Management of root-lesion nematodes in the northern grain region. PR09-4501, Department of Agriculture, Fisheries and Forestry, Queensland Government.

Thompson JP, Owen KJ, Stirling GR, Bell MJ (2008) ‘Root-lesion nematodes (Pratylenchus thornei and P. neglectus): a review of recent progress in managing a significant pest of grain crops in northern Australia.’ Australasian Plant Pathology 37: 235?242.

Thompson JP, Clewett TG, Sheedy JG, Reen RA, O’Reilly MM (2009) ’Occurrence of root-lesion nematodes (Pratylenchus

thornei and P. neglectus ) and stunt nematode (Merlinius brevidens) in the northern grain region of Australia? Australasian Plant Pathology 39: 254 – 264.

Tolerance and resistance of wheat varieties to root-lesion nematodes are published each year at nvtonline.com.au or in Wheat Varieties for Queensland, GRDC/QDAFF.

 

Authors: Kirsty Owen, Jason Sheedy and Nikki Seymour (Queensland Department of Agriculture, Fisheries and Forestry).

The participating organisations accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.