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FIELD VARIATION OF ABIOTIC FACTORS AND THEIR RELATIONSHIP WITH NEMATODE COMMUNITIES IN SUGARCANE

The abundance and distribution of nematodes in the soil is influenced by biotic and abiotic soil factors. A previous study based on soil samples collected over a large part of KwaZulu-Natal showed that numbers of Pratylenchus, Helicotylenchus and Paratrichodorus were inversely related to pH and positively related to iron levels in the soil. Weaker relationships occurred between both aluminium and manganese and the three nematode genera. In contrast, numbers of Xiphinema showed no strong association with any of the soil characteristics. To determine whether the same relationships occurred on a much smaller scale, a study was made of the levels of certain abiotic soil factors and the distribution of the plant parasitic nematodes in a single sugarcane field. The data were derived from soil samples collected from five, adjacent, 200m rows across the field. Xiphinema elongatum dominated one part of the five transects while Helicotylenchus dihystera dominated the other part. The relationship between the soil elements and the nematodes differed from that found in the large scale survey. Co-inertia analysis showed a strong positive association between the numbers of H. dihystera and levels of magnesium in the soil whereas the reverse was true for X. elongatum. There was also a strong positive association between the numbers X. elongatum and levels of phosphorus. H. dihystera showed a positive association with most of the soil cations. The opposite was true for X. elongatum. The differences between the two studies are thought to be a consequence of the difference in scale.