Evaluating the Efficacy of Essential Oil Seed Treatments to Reduce Verticillium Wilt of Potato in the Greenhouse.

Verticillium dahliae (VD) is a persistent soil borne pathogen of potato that, left untreated, can cause early plant death, lead to significant yield loss, and subsequent economic loss. Soil fumigation for disease prevention is standard grower practice, which is both expensive and highly regulated.  Sixteen seed treatments were evaluated as possible alternatives to reduce VD severity, including carvacrol, clove, salicylic acid, CaCl₂, and ammonium phosphate.  Single nuclear potato seeds were planted into individual pots (25.4 cm diameter and 22.86 cm deep) containing 11.34 kg of sterilized sandy loam soil in two separate greenhouses in a randomized complete block design in Hermiston, OR.  Plants were inoculated with 50 ml of a 10⁶ conidial suspension 21 days after full emergence and were destructively sampled 21 days later.  Plants emerged 18 to 26 days after planting in one greenhouse and 22 to 46 days after planting in the other.  Despite concerns that certain essential oils would be phytotoxic, there were no differences in emergence rates or times by treatment.  Although there were differences in plant height and vigor by block in both greenhouses, these differences were not observed by treatment.  In one greenhouse, more VD propagules per ml of plant sap were measured for eight of the treatments as compared to the uninoculated control: salicylic acid, garlic, carvacrol + CaCl₂, salicylic acid + CaCl₂, salicyclic acid + ammonium phosphate, carvacrol + ammonium phosphate, clove, and a tween 80 solution.  No treatment differences were measured in the second greenhouse but similar trends were observed in the best performing treatments.  Previous lab data suggests that essential oils are effective in controlling VD growth in vitro.  This research demonstrates that there may be an opportunity to reduce VD using essential oils in vivo, although further research is required to evaluate best application method and rates, product costs, and in field implementation, to confirm disease reduction before these treatments are applied in a commercial setting.