Nematode-resistant rotation and cover crops
Plant-parasitic nematode are important pest of many crops and growing nematode-resistant rotation and cover crops plays an important role in managing nematode pests.
A range of potentially useful crops have been tested for resistance to root-knot nematode in Australia and the results can be found in two publications:
As part of work in many projects in Queensland, useful crops have also been tested for resistance to a range of other plant-parasitic nematodes. This work has been collated and presented in this key and will be added to as new information becomes available.
Resistance ratings are based on greenhouse trials in pots. Levels of resistance or susceptibility are determined by inoculating plants with a known number of nematodes (the initial population density, Pi), measuring the final population density (Pf) and then determining the reproduction of the nematode on the crop (i.e. Pf/Pi).
Highly Resistant (HR) The nematode does not reproduce on these crops. When a highly resistant crop is grown, there will be no more nematodes present at the end of the crop than when it was planted.
Resistant (R) Virtually no reproduction occurs on these crops. As with highly resistant crops, there will be no more nematodes present at the end of the crop than when it was planted.
Slightly Susceptible (SS) Limited reproduction occurs on these crops. Nematode populations will increase to levels capable of damaging crops.
Moderately Susceptible (MS) These crops are good hosts of the nematode. Nematode populations will increase 10 -100 times.
Highly Susceptible (HS) These crops are excellent hosts of the nematode. Nematode populations will increase more than 100 times.
As crops may be resistant to some species of plant-parasitic nematodes and not others, it is important to know which nematode species is present in a particular field.
For root-knot nematode, as there are a number of root-knot nematode species in Australia, a rotation or cover crop with resistance to that particular species should be selected. Alternatively, a crop that is resistant to all known species of root-knot nematode can be chosen. Unfortunately, information on the resistance of newly-released cultivars is usually not available because the appropriate screening work has not been undertaken.
The results presented in this key are from greenhouse trials undertaken in Queensland. As they may not be indicative of host susceptibility in the field, further assessment by growers in the field under local conditions is recommended.
Advice should be sought on the suitability of any rotation or cover crop for growing in a particular region, and for its ability to harbour pathogens of relevance to the intended cash crop which follows.
Katherine Thomson, Jennifer Cobon, Wayne O'Neill and Tony Pattison
Department of Agriculture and Fisheries Queensland