Some Effects of Abiotic Stress on Infection of Dyer’s Woad (Isatis tinctoria L.) by Puccinia thlaspeos C. Schub.: Implications for Biological Control

Problem statement: The rust pathogen, Puccinia thlaspeos, is being studied as a potential biocontrol agent for the noxious weed dyer’s woad. Although its disease etiology is well understood, very little has been learned about the effect of environmental stresses on infection. Approach: Dyer’s woad plants were exposed to different levels of oxidative stress, salinity stress, osmotic stress, dehydration, and cold stress before being inoculated with the rust pathogen. Rust infections were subsequently detected in asymptomatic tissue using rust-selective primers with the polymerase chain reaction. Results: Mild abiotic stress appears to enable dyer’s woad plants to develop cross-tolerance to the rust pathogen. Plants exposed to the mildest level of salinity were only 60% infected. Those exposed to the lowest osmotic stress were only 50% infected while plants exposed to the shortest period of dehydration, or cold stress were both only 70% infected. Control plants were 100% infected for all experiments. On the other hand, exposing plants to mild oxidative stress did not lower infection while the highest level of oxidative stress significantly lowered infection to 55%. Conclusion: Crosstolerance to multiple stresses often a desirable trait for plants of economic importance, is a cause for concern in biocontrol of weeds because of its potential to adversely impact the efficacy of mycoherbicides.