Some Observations On the Orientation of Ditylenchus Dipsaci and Invasion of Oat Seedlings

Abstract

In sand fractions with particles of diameter larger than 150 u, the speed Ditylenchus dipsaci larvae migrated was closely correlated with the number that invaded oat seedlings within 3 days of inoculation. Migration was fastest and invasion rates highest at the flex point of the moisture characteristic of each sand when the pores were draining. In either sand or aseptic conditions on agar, larvae accumulated around seedlings even when the larvae were separated from the seedlings by dialysis membranes. In the rhizosphere, larvae appeared to orientate along a concentration gradient of secretions from the plant, whereas elsewhere they moved at random. Not all the larvae that arrived at a root stayed there. Accumulation depended on fewer leaving than arriving and also on the moisture content of the sand. Larvae belonging to the oat, red clover, lucerne and daffodil races were attracted to oats and most accumulated at the root-stem junction of oat seedlings.