Nematode Interactions Unit

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New cyst nematode threats to cereals in the UK

For the past 35 years cereal cyst nematodes (CCN) have been a minor problem in intensive cereal production in the UK and many other areas of northern Europe, despite the susceptibility of most cereal cultivars to these widespread pests. Historically, the principal cereal cyst nematode, Heterodera avenae has been controlled by parasitic fungi that destroy the females and eggs of the nematode and which have built up in cereal monocultures. This phenomenon is an example of the natural control of a pest in an intensive agriculture system.

In nematode surveys conducted at Rothamsted Research the cereal cyst nematode, Heterodera filipjevi was found in fields in Essex and in Wales. This pest had not been recorded in the UK and is currently a significant pest in Scandinavia and elsewhere in continental Europe. The research project described aimed to assess the risk of H. filipjevi to intensive cereal production in the UK. The research results are summarised in the following statements:

CCN populations were more diverse than expected. In a limited survey of cereal fields in the UK 65% were infested with cereal cyst nematodes and H. filipjevi was widespread. Heterodera pratensis was also present at one site but morphological, biochemical and host range studies confirmed that most fields contained mixed populations of H. avenae and H. filipjevi.

All CCN populations were suppressed by parasitic fungi that destroyed nematode females and eggs.  Cyst nematode populations containing H. filipjevi only produced a single generation in a growing season and their ability to multiply on wheat was similar to that of H. avenae, which also has a single generation. Nematode females and eggs in all populations studied were parasitised by fungi including Catenaria auxiliaris and Pochonia chlamydosporia that were also known to infect H. avenae. The amounts of parasitism observed indicated that these fungi were major factors in limiting nematode reproduction on susceptible crops.

The principal CCN pests had different responses to some plant defence compounds.  DIBOA a hydroxamic acid produced by wheat and rye as a plant defence compound reduced the hatch and mobility of juveniles of H.avenae and increased their mortality more than of those of H. filipjevi that recovered from exposure to such compounds.

These findings suggest that H. filipjevi is not a significant new threat to intensive cereal production in the UK and it is effectively controlled by those fungi that have successfully controlled the closely related H. avenae for many years. The unexpected widespread distribution of H. filipjevi in the UK may have resulted from the current predominance of autumn-sown cereals but this would need further testing.