ROOT LESION NEMATODE (RLN)

The two important species of root lesion nematode (RLN) common in Victorian cropping soils are Pratylenchus neglectus and Pratylenchus thornei; they often occur together. RLN can cause large grain yield losses, particularly in wheat and chickpea crops. At least 20 percent of cropping paddocks in south eastern Australia have populations of RLNs high enough to reduce yield. Over 90 percent of paddocks in the Wimmera and Mallee regions have RLNs present.

What to Look For

In the field, symptoms include stunted growth, uneven patches or waviness across the paddock. The two main root symptoms include lesions or discolouration of the roots and a lack of branching along the main roots, (Figure 3.19). Unlike the cereal cyst nematode, root lesion nematodes do not cause the roots to swell or knot and no cysts are produced.

Figure 3.19 Roots infected with Pratylenchus nematodes have dark lesions and lack lateral roots

Disease Cycle

Root lesion nematodes are worm-like organisms less than 1 mm in length which feed on root tissues (Figure 3.21). Unlike cereal cyst nematode, the RLN has more than one generation per season and is able to migrate between and within the roots and soil, (Figure 3.20). These nematodes survive over summer in a dehydrated state, becoming active again once moisture is available.

Figure 3.20 Disease cycle of root lesion nematode in cereals.

Illustration by Kylie Fowler

Figure 3.21 Pratylenchus thornei adult female, approximately 0.65 mm in length. Image courtesy Kirsty Owen, University of Southern Queensland

Management

Management of RLN is based on crop rotation. Rotations which include resistant crops will reduce the nematode population in the soil. Susceptible wheats and chickpeas are good hosts of RLN. When grown consecutively, wheat and chickpeas can lead to high nematode populations. The yield loss caused by RLN is related to the number of nematodes present in a paddock. Rotations are the best way of controlling RLN. If growing susceptible crops/varieties, a PreDicta B test can be used to monitor RLN populations and ensure they are not at densities known to cause yield losses.

Resistant crops can reduce nematode populations by up to 50 percent year. A break of two or more years from susceptible crops may be necessary to minimise yield loss if nematode numbers were high to start with. Avoid delayed sowing of intolerant cereal crops.

Hosts

RLNs have a broad host range that includes cereal and broadleaf crops. Table 3.0 summarises the host range. However, always check the current cereal and pulse disease guides for up to date ratings.

RLNs are more likely to be a problem when:

  • susceptible varieties are grown sequentially increasing nematode numbers
  • an intolerant crop is sown, or
  • sowing is delayed.

Table 3.0 Hosting ability of crops to the two common species of root lesion nematodes

Crop P. thornei P. neglectus
Wheat

Barley

Poor – good A

Poor – intermediate A

Poor – good A

Poor – intermediate A

Oat Poor Intermediate
Canola Intermediate Good
Field pea Poor – intermediate A Poor A
Lentil Poor A Poor A
Chickpea Good Good
Vetch Good -
Faba bean Poor Good
Medic Poor Poor
Sub-clover Poor – good Poor

AIn some crops the hosting ability varies between varieties.

Further Information

More detailed information can be obtained from the DEDJTR AgNotes Series www.vic.gov.au/graindiseases

Victorian Cereal Diseases Guide (AG 1160) www.vic.gov.au/cerealdiseaseguide

Victorian Winter Crop Summary www.vic.gov.au/victorianwintercropsummary

Wallwork H (2015) Cereal Seed Treatments (SARDI) http://www.pir.sa.gov.au, www.pir.sa.gov.au, http:// www.pir.sa.gov.au/ data/assets/pdf_file/0005/237920/cerealseedtreat2015_web.pdf

Root-Lesion Nematodes Tips and Tactics (GRDC) www.grdc.com.auhttp://www.grdc.com.au/Resources/Factsheets/2015/03/Root-Lesion-Nematodes

PreDicta B: a soil analysis service delivered by accredited agronomists. PreDicta B can detect P. neglectus, P. thornei and a range of soil-borne diseases. Contact your local agronomist, or to locate your nearest supplier, email your contact details and location to: shawn.rowe@sa.gov.au or visit http://www.pir.sa.gov.au/ research/services/molecular_diagnostics

CROWN ROT

Bunts and Smuts of Cereals