Document: DEN-3-46-22

Impacts of combined leaf damage and Plasmodiophora brassicae root infection on Brassica rapa.

FRANKE, D.M.* and A.E.WEIS

University of California - Irvine, Irvine, CA 92697 ¹

Abstract:
In this paper, we compare the individual effects of leaf damage (clipping) and of infection with the root pathogen Plasmodiophora brassicae with the effect of combined leaf damage and root infection. We also compare the effects of early (3-leaf rosette stage) and late (at bolting) leaf damage to see whether the timing of defoliation altered the impact on plant fitness. We found that control plants, which were not exposed to leaf damage or the root pathogen, produced more seed and were larger than plants in all other treatments. Plants that were clipped and infected with the fungus produced less seed than plants that were only clipped or only inoculated, as was expected. Moreover, many of the plants that were both clipped and infected died without producing any seed, while death was rare for plants in any other treatments. This demonstrates that experiencing two types of damage - in this case leaf damage and root infection - can have a much more severe impact on plants than the sum of the independent impacts of those types of damage. With regard to the timing of leaf damage, we found that plants that were only clipped produced more seed when they were clipped late than when they were clipped early. However, if plants were both clipped and infected, plants that were infected and clipped early produced more seed than plants that were inoculated and clipped late. In this case, the presence of a second type of damage (or second natural enemy) reversed the pattern observed when only a single type of damage was considered.

Keywords: Brassica, Plasmodiophora, clubroot, leaf damage, ecological interactions, phenology, timing of damage

This abstract is being presented at: 4:30 PM in session:
Oral Session #31: Agroecology.