2019 ASHS Annual Conference

This study examined lowering pH of nutrient solution as a new management strategy to mitigate the risk of oomycete disease incidence without influencing plant growth. Although pH below 5.0 has been shown to negatively affect oomycete pathogen growth, hydroponic nutrient solution is typically maintained within pH 5.5-6.5, as plants tend to exhibit growth inhibitions outside of this range. Nevertheless, growth inhibitions can typically be attributed to pH-dependent factors affecting nutrient availability, which may be mitigated by taking precautionary measures. We hypothesized that if plants can be grown in pH below 5.0, the risk of oomycete disease incidence may be reduced. As first steps towards development of a new nutrient solution management strategy, we determined if adjusting micronutrient concentrations in solution based on reported availability levels was effective in mitigating plant growth inhibition typically experienced at low pH. Basil and spinach plants were grown in hydroponic systems with pH maintained at 4.0, 4.5, 5.0, or 5.5. Two nutrient solutions (with and without micronutrient adjustments) were applied at each pH level, where concentrations of copper, zinc, manganese, and boron were decreased by one-half and molybdenum concentration was doubled in the adjusted solution. To our surprise, basil plant growth was not affected by pH for a range of 4.0-5.5 or nutrient solution adjustment. Alternatively, spinach plant growth was significantly reduced in pH below 5.0. Using basil plants, we examined the efficacy of lowering pH in preventing Pythium infection. Nutrient solution pH was maintained at 4.0 or a conventional range (pH 5.5-6.5) and inoculated with Pythium aphanidermatum zoospores. Disease symptomology was almost exclusively limited to pH 5.5-inoculated treatments. Additionally, fresh plant mass was significantly reduced in pH 5.5-inoculated. The results of this study indicate that low pH (pH 4.0) can effectively suppress Pythium aphanidermatum disease incidence after zoospore inoculation without influencing basil plant growth.