HORIZONTAL SPREAD OF BEET NECROTIC YELLOW VEIN VIRUS IN SOIL

Horizontal dispersal of beet necrotic yellow vein virus (BNYVV) by mea ns of viruliferous zoospores of Polymyxa betae was studied in greenhou se experiments. BNYVV was not detected in roots of sugar beet plants g rown in silver sand for 4 weeks at a root-free distance of 5 cm from e ither P. betae- and BNYVV-infected plants or BNYVV-infested soil. Spre ad of BNYVV from inoculum sources in the field was studied in the abse nce and presence of tillage practices. Active dispersal in combination with root growth from and towards point sources of inoculum contribut ed only little to horizontal dispersal of viruliferous inoculum and sp read of disease during the season, as determined for one soil type, tw o different years and in the absence of tillage and tread. In the seco nd beet crop after application of inoculum to whole field plots, more BNYVV-infected plants were detected at 2 m than at 8 m distance from t he infested plots in the tillage direction. In the third year, disease incidence at 8 m was high and equivalent to that at 2 m.