Root pathology and symptoms of nematodes attacking apple roots

A total of 302 root and soil samples were taken in all the major Western Cape apple producing areas to determine if it is possible to use root symptoms to predict nematode numbers in apple orchards.  Roots were examined for stubbiness, discolouration, abnormal root appearance, root lesions and galls.  Apart from a general nematode soil extraction method, specific extraction methods for lesion and dagger nematodes were also used.

Complete chemical and mechanical soil analysis were also done on every soil sample.

1. The hypothesis that root symptoms can be used to predict nematode numbers could not be proved.
2. There are also other factors besides nematodes that cause discoloured, stubby abnormal roots.
3. Woolly apple aphid (WAA) was often associated with abnormal roots. The role of WAA in causing root damage should be researched.
4. Soils with a clay content of less than 2,5% had significantly higher numbers of the dagger nematode species Xiphinema americanum, X. diffusum and X. elongatum than soils with a higher clay content.
5. Soil carbon content was not correlated with higher numbers of free-living, non-parasitic nematodes.
6. The Flegg’s decanting and sieving method extracted 1,69 times more Xiphinema than the centrifugal-flotation extraction method.