Root Lesion Nematode – South Australia

 

Key Points

• Root lesion nematodes (RLN) reduce development of lateral roots, which decreases the ability of plants to extract water and nutrients.


• 
  Pratylenchus neglectus and Pratylenchus thornei are the main root lesion nematodes causing yield loss in the southern agricultural region of Australia.


• Wheat is the main host; however varieties vary in resistance and tolerance.


• Traditional break crops can also be hosts; host range varies for each Pratylenchus species.


• Yield losses can be reduced by rotation with resistant and tolerant crops and varieties, good nutrition and sowing early.

 

Background

Root lesion nematodes emerged as potential problems in cereals (and other crops) after management strategies were implemented to control cereal cyst nematode and take-all. Yield losses in the southern region are variable and currently under investigation, but present estimates for intolerant varieties indicate a 1 % yield loss per 2 nematodes per gram soil. Pratylenchus thornei occurs throughout the root zone and is often more damaging than P. Neglectus, which tends to be concentrated in the top 15 cm of the soil.

Root lesion nematodes survive summer as dormant individuals in dry soil and roots, and become active after rain. They can survive several wetting/drying cycles. About three generations of the nematodes are produced each season, with the highest multiplication in spring.

 

Symptoms

Crop symptoms of RLN are not distinctive and can be easily overlooked. The typical symptom in the southern region is large areas of poor crop vigor (figure 1) due to poor root growth. In cereals, affected roots may be discoloured and have reduced lateral branches (figure 2).

 

Figure 1: Poor vigor wheat in high RLN plot (left) compard to healthy plot with low RLN (right). (Photo: Grant Hollaway)

 

Figure 2: Discolouration and lack of lateral roots on cereals is caused by root lesion nematodes. (Photo: Frank Henry)

 

In chickpeas, roots show brown lesions where nematodes enter the roots (figure 3). When infected roots are stained and examined under the microscope, nematodes can be seen inside the roots (figure 4). For accurate diagnosis, the plant root systems should be examined by a plant pathologist.

 

Figure 3: Distinctive brown lesions on chickpea roots indicate root lesion nematode infection. (Photo: Vivien Vanstone)

 

Figure 4: Stained nematodes feeding in the root cortex. (Photo: Adbol Taheri)

 

Management

Root lesion nematodes are not necessarily controlled by traditional ‘break’ crops; research is progressing to check for cultivar variation. Crops that can control both P. Thornei and P. Neglectus, include narrow leaf lupin, triticale and some pea cultivars (table 1).

 

Table 1: Susceptibility of some non-cereal crop and pasture species to root lesion nematode infection.

RLN Species
Susceptible
Moderately susceptible
Resistant


Pratylenchus neglectus
canola, chickpea, mustard
common vetch, lentil
field pea, narrow leaf lupin, faba bean, triticale, safflower, cereal rye, medic, clover


Pratylenchus thornei
chickpea, vetch, faba bean
canola, mustard, field pea*, lentil
field pea*, lupin

 

*New field pea varieties are more susceptible to P. Thorneithan older varieties, check classification of specific varieties.

 

The PreDicta B soil test done prior to sowing can quantify both nematodes. This information is useful to help plan a cropping program to manage RLN. Check current Cereal Disease Variety Guides to identify which varieties have useful resistance and tolerance. Minimise the use of susceptible crops or varieties. More than one break crop is often needed to reduce high numbers.

Controlling any ‘green bridge’ between crops helps prevent early multiplication of the nematodes. If you are growing intolerant crops or varieties, sow at the optimum time and provide adequate nutrition to reduce yield losses.

 

Further reading and references

Wallwork H (2000) Cereal Root and Crown Diseases, Grains Research & Development Corporation and South Australian Research and Development Institute.

Wallwork H (2013) Cereal variety disease guide 2013 fact sheet, South Australian Research and Development Institute and Grains Research & Development Corporation.

 

Author: Alan McKay (South Australian Research and Development Institute) alan.mckay@sa.gov.au

 

 

The National Soil Quality Monitoring Program is being funded by the Grains Research and Development Corporation, as part of the second Soil Biology Initiative.

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.