Root Lesion Nematode

Pratylenchus neglectus, Pratylenchus thornei and Pratylenchus zeae

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 Barley, Sorghum or resistant cultivars are planted.
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.

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.

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.

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 and Triticale are resistant and are good break crops. Canola is susceptible to Pratylenchus neglectus and moderately resistant to Pratylenchus thornei.
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 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.

Related and Similar Species:

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

References:

1295

Acknowledgments:

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