SUMMARY

Observations on tillering and the build-up of nematode populations on sugar-cane both in light (sandy) and heavy (clayey) soils may give information on how nematodes reduce yields. It has been shown by plant physiologists that the emergence of stems after planting is directly related to the development of.the roots on the setts. The authors have observed that nematodes only multiply abundantly on the roots produced by the sett during the emergence of the stem. The attacks on these roots lead to a reduction in the number of stems, prhich is known to be directly correlated to yield reduction. In sandy soils, nematodes heavily attack sett-roots immediately, thus, disturbing primary and secondary tillering, but in heavy Clay soils nematode attacks are slower and only interfere with secondary tillering, this explains why, on heavy soils, yield reduction is generally less marked although nema-tode populations are often higher. These observations may also indicate what effect nematodes will have ony ields in the first weeks after planting. The authors conclude that: i) research concerning tolerant sugar-cane cultivars should aim a t selecting those with a large, quick developing and rapidly renewed root system on setts, i i) nematicides should be selected for their ability to control early nematode attacks. RÉSUMÉ Mécanisme de l’action pathogdne des nimatodes sur la canne à sucre en culture irrigue’e Il est connu que l’effet des traitements nématicides sur canne à sucre est beaucoup plus faible en terrain lour