Monitoring Spongospora subterranea Development in Potato Roots Reveals Distinct Infection Patterns and Enables Efficient Assessment of Disease Control Methods

Abstract

Spongospora subterranea is responsible for significant potato root and tuber disease globally. Study of this obligate (non-culturable) pathogen that infects below-ground plant parts is technically difficult. The capacity to measure the dynamics and patterns of root infections can greatly assist in determining the efficacy of control treatments on disease progression. This study used qPCR and histological analysis in time-course experiments to measure temporal patterns of pathogen multiplication and disease development in potato (and tomato) roots and tubers. Effects of delayed initiation of infection and fungicidal seed tuber and soil treatments were assessed. This study found roots at all plant developmental ages were susceptible to infection but that delaying infection significantly reduced pathogen content and resultant disease at final harvest. The pathogen was first detected in roots 15–20 days after inoculation (DAI) and the presence of zoosporangia noted 15–45 DAI. Following initial infection pathogen content in roots increased at a similar rate regardless of plant age at inoculation. All fungicide treatments (except soil-applied mancozeb which had a variable response) suppressed pathogen multiplication and root and tuber disease. In contrast to delayed inoculation, the fungicide treatments slowed disease progress (rate) rather than delaying onset of infection. Trials under suboptimal temperatures for disease expression provided valuable data on root infection rate, demonstrating the robustness of monitoring root infection. These results provide an early measure of the efficacy of control treatments and indicate two possible patterns of disease suppression by either delayed initiation of infection which then proceeds at a similar rate or diminished epidemic rate.

Germinate to exterminate: chemical stimulation of Spongospora subterranea resting spore germination and its potential to diminish soil inoculum

“…It is possible that earlier and greater zoospore release contributed to greater disease in the tomato bioassay. It has been previously demonstrated that early root infection results in greater root and tuber disease in potato hosts than if infection is delayed by several days (Thangavel et al, 2015). However, while presence of more zoospores would probably increase the chance and rate of root infection, prior studies have shown that presence of large numbers of sporosori in soil does not always result in severe disease (Van De Graaf et al, 2005).…”

“…The concentration of S. subterranea DNA in each soil sample was determined by quantitative PCR (qPCR) following the protocol of Thangavel et al (2015). Primers for quantification of S. subterranea (SPO10, SPO11, Probe) were from the ribosomal ITS region (Hernandez Maldonado et al, 2012).…”

Susceptibility of opium poppy and pyrethrum to root infection by Spongospora subterranea

“…Testing for root infection by S. subterranea followed the method of Thangavel, Tegg, and Wilson (). Root samples from each plant (50 mg) were cut into small pieces, and DNA was extracted using the DNeasy PowerPlant Pro Kit DNA isolation kit with RNAase treatment (Qiagen Group, Germany).…”

Zoosporangial root infection of tomato by Spongospora subterranea in hydroponic and glasshouse culture results in diminished plant growth

“…Root disease thus progresses in a polycyclic manner (Merz & Falloon, ). The initial infection of the roots of a susceptible host can occur throughout the plant growth cycle; however, an early host–pathogen interaction will lead to greater disease than if the first infection is delayed (Thangavel, Tegg, & Wilson, ).…”

“…growth cycle; however, an early host-pathogen interaction will lead to greater disease than if the first infection is delayed (Thangavel, Tegg, & Wilson, 2015).…”