Metabolomes of Potato Root Exudates: Compounds That Stimulate Resting Spore Germination of the Soil-Borne Pathogen Spongospora subterranea

Abstract

Root exudation has importance in soil chemical ecology influencing rhizosphere microbiota. Prior studies reported root exudates from host and nonhost plants stimulated resting spore germination of Spongospora subterranea, the powdery scab pathogen of potato, but the identities of stimulatory compounds were unknown. This study showed that potato root exudates stimulated S. subterranea resting spore germination, releasing more zoospores at an earlier time than the control. We detected 24 low molecular weight organic compounds within potato root exudates and identified specific amino acids, sugars, organic acids, and other compounds that were stimulatory to S. subterranea resting spore germination. Given that several stimulatory compounds are commonly found in exudates of diverse plant species, we support observations of nonhost-specific stimulation. We provide knowledge of S. subterranea resting spore biology and chemical ecology that may be useful in formulating new disease management strategies.

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

“…The inoculum was approximately 1 year old when used. Inoculum contained approximately 6900 sporosori mg À1 , as determined by suspending 0.1 g of inoculum in 10 mL of water and quantifying using a haemocytometer under light microscopy (Balendres et al, 2016a).…”

“…Previous studies (Ledingham, 1934;Kole, 1954;Merz, 1989Merz, , 1992Merz, , 1997 indicated that zoospore release could be stimulated by incubation of resting spores in Hoagland's solution (HS). The first direct measurement of stimulation of zoospore release by HS was recently reported, but the specific chemical(s) involved was not determined (Balendres et al, 2016a).…”

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

“…Individual disease lesions were excised using a scalpel, oven‐dried for 4 days at 40°C, ground to a powder with a mortar and pestle and stored at 4°C until use. The inoculum contained an estimated 6,900 sporosori mg −1 determined by suspending 0.1 mg of inoculum in 10 ml water and enumerating using a haemocytometer with a light microscope (DM 2500 LED; Leica Microsystem, Germany; Balendres et al., ).…”

“…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, ). Released zoospores migrate towards roots of susceptible hosts, aided most likely by chemotaxic attraction to root exudates, where they encyst and transfer their cell contents into the root epidermis cell.…”

Not in your usual Top 10: protists that infect plants and algae

“…Powdery scab and root galling susceptibility differ across potato cultivars (Bittara et al, 2016;Falloon et al, 2003), but no genetic basis of resistance has yet been identified. Metabolites of potato root exudates induce S. subterranea resting spore germination, but as L-glutamine and tyramine have the strongest effects, this might not be host specific (Balendres et al, 2016). This may explain reports of primary infection by S. subterranea in a range of nonsolanaceous host plants (Merz and Falloon, 2009).…”