Delaying Spongospora induced root infection in potato roots by altering inoculation dates and chemical treatment

Spongospora subterranea is an obligate, soil-borne pathogen that produces necrosis and galling on roots and powdery scab on potato tubers. The polycyclic nature of infection and the fact that a dormant sporeball produced can survive for long periods in the soil makes this pathogen a concern for potato growers. Epidemiological knowledge of the critical root infection phase is not fully understood making disease management difficult. Our study sought to track the infection process and identify whether delaying infection by altering the inoculation date could reduce root and tuber-based symptom development. Additionally a range of seed and soil treatments were applied in both glasshouse and field trials to see if this could also negate disease development. Disease progress was tracked through multiple sequential assessments which included counts of zoosporangial and quantification of pathogen DNA by qPCR in roots. Root gall formation and tuber disease was also measured. Early inoculation produced greater disease whereas later inoculation slowed disease progression. Some chemical treatments including tuber treated or in furrow application of Fluazinam and Mancozeb also slowed disease progression as demonstrated by lower levels of S. subterranea in the root and reduced galling and tuber disease, compared to untreated control treatments. The most effective chemicals have potential to minimise the disease reduction but not completely. These results also indicated that tracking the early infection process via root qPCR detection of Spongospora provides an early measure of the efficacy of various treatment options, with this technology a viable option for better understanding disease management and control.