Root Lesion Nematode

Pratylenchus neglectus, Pratylenchus penetrans, Pratylenchus quasitereoides, Pratylenchus thornei and Pratylenchus zeae.

Pratylenchus quasitereoides was formerly called Pratylenchus teres

Description:

A tiny worm like organism that is less than 1 mm long and feeds on the young roots of many legumes and grasses. They produce stunting, reduced tillering, ill thrift, greyness and wilting in cereals. Where nematode numbers are very high plants may show almost total yellowing. There may be fewer lateral roots and fewer root hairs. Brown, indistinct lesions or spots may be present on the roots.
It is most common where Wheat has been grown continuously for a number of years. There may be patches of poor crop growth and the patches are usually indistinct with ill defined edges. Nutrient deficiency symptoms may also become apparent as the nematodes damage the root system. Root appearance is similar to fungal attack by Take-all and Rhizoctonia.
It is often easiest to detect in the field where Barley (which is resistant) is grown alongside a Wheat crop or where a number of varieties of differing tolerance are grown in close proximity.

Species Affected:

Wheat, Soybeans, Chickpeas, Faba Beans and most legumes are susceptible.
Oilseeds, pastures and legumes may be attacked.
Some Wheat varieties are tolerant.
Barley, Sorghum and Sunflowers are resistant.

Biology:

Nematode numbers usually build up when susceptible Wheat or legumes are planted and are decreased when Sorghum or resistant cultivars are planted.
In WA numbers increased with wheat>barley>canola>pasture>lupins and numbers remained constant under field peas (Harries 2018).
There are 3-4 generations of nematode per year. These may occur within the root so the soil numbers may be relatively low whilst root numbers are high.
Numbers multiply rapidly as the soil temperatures increase.
There may be up to 10,000 nematodes per gram of root.
Late sown crops are generally affected more than early sown crops.
The multiplication rate for P. neglectus was 16, 8, 5 and 1 times for wheat, barley, canola and lupins respectively in a 2015 trial at Wongan Hills (Collin s 2017).
The multiplication rate for P. quasitereoides was 16 for barley and canola, 13 for wheat and 2 for lupins in a 2015 trial at Gibson near Esperance (Collins 2017).

Life Cycle:

The nematode moves through to soil in water films to the hosts roots. Females lay eggs as they move through the root tissue. The eggs hatch and the young nematodes swim to new young roots. There may be 3-4 generations per year. Nematodes survive over summer in a dry form in soil or in dead root tissue and emerge when rain wets the soil.

Origin and History:

Pratylenchus neglectus was recorded in Germany in 1924.

Distribution:

More common on heavy black or grey clay soils.
Pratylenchus neglectus is the most common species in the Southern Australian wheatbelts.
Pratylenchus thorneii is more common in the North eastern wheatbelts.
Pratylenchus quasitereoides occurs in WA and is relatively uncommon in the eastern states.
Pratylenchus thorneii and Pratylenchus penetrans are rare in WA.

Significance:

Pratylenchus thorneii usually causes more damage than Pratylenchus neglectus.
Affected crops often compete poorly with weeds, have reduced nutrient uptake and suffer more from waterlogging, drought and other stresses.
Yield losses in Wheat are usually around 5-10% and 5-20% in Barley in WA.
Root lesion nematodes cost the Australian wheat industry A$134 million in 2009 as below.

 Northern Southern Western Australian 
Root Lesion NematodePotentialActualPotentialActualPotentialActualPotentialActual
Pratylenchus crenatus00000000
Pratylenchus neglectus218113311323326673
Pratylenchus penetrans0000102102
Pratylenchus teres0000349349
Pratylenchus thornei1043852910316750
The Potential and Actual costs of Root Lesion Nematodes to the Australian Wheat Industry in A$ millions 2009. (Murray and Brennan, 2009)
Yield losses in canola have averaged 16% (11-22%) with 17 root lesion nematodes per gram of soil and common canola varieties were all susceptible (Collins 2017). Yield losses in wheat were around 11-18% and were around 10-19% in barley and most common varieties are susceptible.

Symptoms

In cereals
Patches of poor growth
Stunted plants
Stunted roots with few lateral branches
Roots with brown lesions from nematode feeding
Yellowing plants especially on the lower leaves
Premature wilting or dying under drought stress.
Poor tillering
In canola there are no obvious symptoms

Management and Control:

Avoid rotations with successive susceptible crops.
Do a PreDicta B soil test which is available from SARDI Root Disease Testing Service.
Plant tolerant or resistant cultivars. See Susceptibility of crops and pastures to Pratylenchus species. Tolerant cultivars will tolerate larger numbers of nematodes and resistant cultivars reduce nematode reproduction leading to lower numbers in following seasons. Faba Beans, Field Peas, Lentils, Lupins, Oats, Rye, Triticale and Sunflowers are resistant and are good break crops. Lupins are highly susceptible to Pratylenchus penetrans but tolerant of to other species. Canola is susceptible to Pratylenchus neglectus and moderately resistant to Pratylenchus thornei. Determining the species present in the paddock is important.
On average for the cereals, triticale is more tolerant than barley which is more tolerant than wheat.
Ensure adequate nutrition and weed control.
Control summer weeds.
Increase cultivation.
Test soil for nematode numbers before planting.
During the growing season AgWest can test plants and soil for nematode numbers
It usually takes 2 years of break crops to reduce nematode numbers significantly.
Note the difference between resistant and tolerant varieties. Resistant varieties prevent the nematode building up and affecting following crops and but they may be seriously affected by the nematodes in the current season. Tolerant varieties are not affected by the presence of the nematode. That is, they tolerate it but may allow numbers to build up and affect subsequent crops.

Thresholds:

Above ground symptoms are hard to distinguish. Infested plants have fewer root hairs, lateral roots and indistinct brown lesions along the roots.
A DNA test is available through SARDI.
Numbers above 0.15 nematodes per mL of soil do not usually cause significant yield losses.

Nematodes
per mL soil
Nematodes
per g dw root
Effect
0-0.20-1000No significant effect on cereal yields
0.2-1.01000-10,000No visual effects. Yield loss up to 15%
1.0-2.010,000-100,000Patches in crop. 15-30% yield loss in patches
> 2.0> 100,000Poor crop growth. 30-50% yield loss
Adapted from Sharma, Wright and Loughman 2001.
This has been updated by McKay et al (2016) for soil infestations as below
Nematodes
per gram soil
Cereal yield loss
0-0.1No significant effect on yields
0.1-2.0Yield loss 0-15%
2.0-15Yield loss 0-30%
>15Yield loss 0-50%

In 2016 40% of WA cereal paddocks had significant root lesion nematode populations.
On average wheat and barley yields are reduced by 270 kg for every 10 root lesion nematodes per gram of soil (Collins 2017).

Related and Similar Species:

Pratylenchus brachyurus
Pratylenchus penetrans
Pratylenchus scribneri
Take-all and Rhizoctonia produce similar lesions on the roots.

References:

(Lamb, 1989)

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.