Interaction effects of two biological control organisms on resistant and susceptible weed biotypes of Chondrilla juncea

• Published in: Phytopathology Vol. 99; no. 6; p. S19
• Main Authors: Campanella, D M, McEvoy, P B, Mundt, C C
• Format: Journal Article
• Language: English
• Published: 01.06.2009
• Subjects: Chondrilla juncea; Eriophyes; Puccinia
• ISSN: 0031-949X

Interactions between natural enemy species may modify their net effect on host plants, but little research has been done to examine how plant resistance influences species interactions in biological weed control. We performed common garden experiments with the invasive plant Chondrilla juncea to compare a rust-susceptible weed biotype with a rust-resistant biotype. Inoculations with two biological control organisms, the rust fungus pathogen Puccinia chondrillina and the eriophyid gall mite Eriophyes chondrillae, were applied separately and in combination to test if plant performance is modified by antagonistic or facilitative species interactions. As expected, genetic resistance of weed biotypes modified the effects of rust disease. We found no significant rust x mite interaction effects for several plant performance traits, and analysis of effect sizes and their confidence intervals supports the conclusion of truly additive interactions. Therefore the two natural enemies appear to have independent and complementary effects on plant performance. However, a competitive indirect effect was detected because rust inoculation reduced the total dry biomass of mite galls in the rust-susceptible biotype due to decreased growth of diseased shoots, but not in the rust-resistant biotype. Our results indicate that rust disease may have the potential to modify mite gall epidemiology as well as relative plant performance in mixed populations of resistant and susceptible C. juncea biotypes.