Resting Spore Dormancy and Infectivity Characteristics of the Potato Powdery Scab Pathogen Spongospora subterranea

Abstract

The soil‐borne potato pathogen Spongospora subterranea persists in soil as sporosori, which are aggregates of resting spores. Resting spores may germinate in the presence of plant or environmental stimuli, but direct evidence for resting spore dormancy is limited. A soilless tomato bait plant bioassay and microscopic examination were used to examine features of S. subterranea resting spore dormancy and infectivity. Dried sporosori inocula prepared from tuber lesions and root galls were infective after both short‐ and long‐term storage (1 week to 5 years for tuber lesions and 1 week to 1 year for root galls) with both young and mature root galls inocula showing infectivity. This demonstrated that a proportion of all S. subterranea resting spores regardless of maturity exhibit characteristics of stimuli‐responsive dormancy, germinating under the stimulatory conditions of the bait host plant bioassay. However, evidence for constitutive dormancy within the resting spore population was also provided as incubation of sporosorus inoculum in a germination‐stimulating environment did not fully exhaust germination potential even after 2.4 years. We conclude that S. subterranea sporosori contain both exogenous (stimuli‐responsive) and constitutively dormant resting spores, which enables successful host infection by germination in response to plant stimuli and long‐term persistence in the soil.

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

“…Soil inoculum was not eradicated by stimulant treatment over the trial periods considered in this study. It has recently been shown that not all resting spores of S. subterranea are responsive to germination stimulation, and that a level of constitutive dormancy exists (Balendres et al, 2017). Thus, regardless of efficiency of distribution within the soil, it would be expected that soil treatment with stimulants might not provide complete disease control.…”

“…The tomato bait test procedure of Balendres et al . (), modified from Merz (), was used to compare the effects of Hoagland's solution and distilled water on root infection. Three‐week‐old healthy tomato (cv.…”

“…These tuber and root diseases are responsible for substantial financial losses to the global potato industry (Balendres et al, 2016b;Falloon et al, 2016;Wilson, 2016). The pathogen persists in the soil for many years between potato crops (De Boer, 2000;Balendres et al, 2017) as aggregates of resistant resting spores called sporosori (Kole, 1954;Falloon et al, 2011). Each of the resting spores within a sporosorus contains a zoospore that, when released, is motile and is responsible for initiating infections in susceptible plant hosts.…”

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

“…subterranea is a soil‐borne protozoan pathogen and is best known as the causal agent of powdery scab in potato tubers (Balendres, Tegg, & Wilson, ; Harrison, Searle, & Williams, ). The pathogen persists in the soil as dormant resting spores aggregated as clusters known as sporosori (Balendres, Tegg, & Wilson, ). Pathogenicity initiates with the germination of the resting spores stimulated by host plant root exudates resulting in the release of short‐lived primary zoospores into the soil (Balendres, Clark, Tegg, & Wilson, ; Balendres, Nichols, Tegg, & Wilson, ).…”

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

“…Spongospora subterranea is known to persist in the soil for many years between potato crops as sporosori, which are aggregates of dormant resting spores (Kole, ; De Boer, ; Falloon, Merz, Lister, Wallace, & Hayes, ; Balendres, Tegg, & Wilson, ). This may be influenced by the presence of alternative host plants that maintain and build soil inoculum during the intercropping period (Falloon, ).…”