The Effects of Chlorine Dioxide on SAR Plant Immunity Responses to a Bacterial Wilt Infection

The objective of this study was to determine the plant immunity effects of two oxidant disinfectants on kidney bean seedlings that were inoculated with a bacterial wilt [Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) (bacterial wilt of common bean)]. Research has shown that chemical signals can increase the Systemic Acquired Resistance (SAR) plant response to plant pathogens and insect herbivory. Oxidants such as chlorine dioxide and hydrogen peroxide may act as signals to increase SAR activities that help defend plants from biotic stressors. The study factors for the kidney bean growth and morphology responses were: 1) oxidants applied either four days before plants were inoculated with the wilt, or four days after plants were inoculated; 2) non-inoculated plants and plants inoculated with Cff; and 3) four oxidant treatments. The four oxidant disinfectant treatments were ClO₂ at 200 ppm (Electrobiocide) and H₂O₂ at 100 ppm (Oxidate) with each oxidant mixed with two different surfactants (EA and Sarc.). The kidney bean plant growth and morphology responses were total leaf area, specific leaf area, total fresh weight, total oven dry weight, and relative growth rate, as averaged across the six plants. The plants were harvested at 48 to 51 days after planting to take the growth and leaf morphology data. Each of the study factors (chemical treatment, inoculation date, and inoculation status) interacted with each other (two, 2-way interactions) in three out of the six main plant growth responses. The total above-ground dry biomass response increased by 35% and 24% for the non-inoculated and inoculated plants, respectively, when the plants were sprayed with EB plus sarcosinate surfactant, at nine days after planting. The study results show that oxidant disinfectants sprayed before the plants were inoculated had increased plant growth. Also, the oxidant disinfectants show some promise for signaling/stimulating natural plant defenses against foliar injury from the bacterial wilt. Future studies should focus on the most effective treatments and increase the number of plant replications in order to reduce variation between treatments.