AN ENVIRONMENTALLY CONTROLLED EXPERIMENT TO MONITOR THE EFFECT OF APHANOMYCES ROOT-ROT AND RHIZOMANIA ON SUGAR-BEET

An experiment was initiated to determine how sugar beets are affected by Aphanomyces cochlioides and beet necrotic yellow vein virus (BNYVV), the causal agents of Aphanomyces root rot and rhizomania, respectively. The experiment was conducted in a controlled temperature box maintained at 27 +/- 2 C. Treatments consisted of soil infested with Aphanomyces, BNYVV, both pathogens combined, and an untreated control. At 8 and 12 wk after planting, leaf and petiole weights and leaf areas were taken. At harvest, tops were removed, and the soil cores were divided into three 15-cm segments and washed. After 8 wk, leaf weights and leaf areas for the control treatment were significantly higher than those for the pathogen treatments. However, after 12 wk, significant reductions in infected beets were seen only when both pathogens were present. Simultaneous infection with both pathogens caused a greater reduction of dry top weight and taproot weight than either pathogen alone. Although the root-rot rating for A. cochlioides was more severe than for BNYVV, there was less weight reduction in the taproot. No differences were detected between the three pathogen treatments regarding the number of roots recovered from the bottom segment of the soil profile, but infected beets had significantly fewer roots than plants grown in noninfested soil.