Powdery scab, caused by Spongospora subterranea, is a significant economic threat to potato production, diminishing yield through root infection leading to root disfunction and reduced tuber quality through the formation of scabby blemishes on tuber skin. S. subterranea is a persistent soil-borne pathogen, producing resilient resting spores that can survive in the soil for over ten years diminishing the efficacy of rotation strategies. The resting spores germinate in presence of a potato crop to release short-lived zoospores that infect potato roots and initiate the disease cycle. A previous study identified 24 low molecular weight organic compounds within potato root exudates, that stimulate the germination of these resting spores and also chemotactically attract zoospores to the roots. Among these compounds, glutamine was found to be the most effective in promoting these processes.
This study investigates the effect of potato varietal susceptibility to powdery scab and root injury on root exudation of key metabolites involved in the initial stages of pathogenesis using UPLC MS/MS approach to analyse for comparison root exudation of in vitro and in vivo grown Kennebec (susceptible) and Gladiator (resistant) cultivars. In the in vitro treatment, plantlets were cultivated in potato multiplication medium for six weeks before transfer to sterile distilled water (SDW) for root exudate collection. To assess root injury effects, 2.5 cm of root tips of the plantlets were trimmed prior to root exudate collection in the SDW. The results showed that glutamine concentrations in root exudates increased with plant age in both cultivars. Additionally, mechanically injured roots exhibited higher glutamine levels compared to intact roots. Across all treatments and plant age periods, Gladiator consistently exhibited higher glutamine concentrations than Kennebec; however, these findings are preliminary and require further validation. In pot trials, root exudates were collected by gradually pouring sterile water over the plant-soil system, including both inoculated and un-inoculated treatments, until 100 mL of leachate drained from the pot. Non-pathogen treatments resulted in elevated glutamine concentrations per milligram of dry root mass in root exudates. A general increase in glutamine concentration was observed with plant age, ranging from four to twelve weeks, except in eight-week-old plants.
This study further explores the application of natural products containing key chemical compounds at planting to divert infective spores away from potato roots by providing competing chemotactic signals, to mitigate the risk of infection. Compared to the untreated pathogen control, all treatments led to a reduction in disease severity. Among the four tested compounds - glutamine, Cu-gluconate, FeEDTA, and potato slurry (a waste byproduct of potato processing) - Cu-gluconate exhibited the highest efficacy in reducing disease severity, decreasing it by 59.1% compared to the controls, followed by glutamine (45.5%). Notably, potato slurry also demonstrated a capacity to suppress powdery scab severity, reducing disease by 43.2% relative to the control.
The goal of this research is to develop a non-fungicidal strategy for managing powdery scab promoting sustainable potato production and economic benefits. By preventing zoospores from infecting tubers, this approach offers an effective alternative for disease control.