Influence of pH, Sulfur, Chloride, and Potassium On Infection Severity of Verticillium dahliae In Russet Burbank Potato Roots

Verticillium dahliae is a soil-borne pathogen that causes a vascular disease of plants and is the primary causal agent of potato early dying disease (PED), PED causes plant death before tubers have finished bulking and can reduce yields by 30-50%. Optimal pH, sulfur (S), chloride (Cl), and potassium (K) concentrations were used to grow potato to determine impacts on Verticillium infection. This was accomplished by inoculating plants grown in hydroponic solutions with varying pH and concentrations of S, Cl, and K. Solution pH levels were maintained at 5.0, 6.0, 7.0, and 8.0 using MES buffer and daily adjustment with HCl or KOH. Low, moderate, optimum, and toxic concentrations of S, Cl, and K were were used to determine influence on Verticillium, all other essential nutrients were kept constant. Impacts of these treatments on Verticillium development were tested by inoculation of each treatment solution with 40 ml of a 100,000 spore per ml solution and by growing plant roots in this inoculated, 14 L solution. Infection was evaluated in two ways after growing plants for 30 days; first, through culturing on modified potato dextrose agar (mPDA) and second, through DNA extraction and quantitative PCR with specific primers. Comparative analysis of DNA produced infection coefficients (IC) relating the total DNA of both potato and V. dahliae. As pH levels increased from 5 to 8 the IC increased indicating higher levels of V. dahliae in the potato roots. Neither solution K nor Cl levels significantly influenced IC levels. However, as solution S levels increased, the IC values significantly increased, suggesting that S nutrition promotes higher infection of V. dahliae. There was also a significant Cl x S interaction on infection. Our preliminary findings suggest a need to minimize S application in fertilizers to reduce PED in Russet Burbank potatoes.