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Tomato plants are highly susceptible to root infection by Spongospora subterranea and are commonly used as bioassay hosts. The impacts of root infection with S. subterranea on plant productivity and yield have been debated. Recent experiments with potato, the major economic host of S. subterranea, have indicated significantly reduced plant growth and potato yield following heavy infection. However, there have been very few similar studies that have examined the possible impacts of S. subterranea infection on tomato plant growth. Three tomato cultivars, “Grape,” “Roma” and “Truss,” were challenged with S. subterranea inoculum in hydroponic culture. Moderate to severe zoosporangial infections were observed with minor but statistically significant differences in susceptibility among the three tomato cultivars. Zoosporangial root infection in the absence of root gall formation resulted in significantly diminished shoot lengths and plant fresh weights in pathogen challenge tests conducted both in hydroponic culture and glasshouse‐grown plants in potting mix. Root lengths were reduced, but the differences were statistically significant in a single trial only. The findings from this study demonstrate that, as with potato, root infection by S. subterranea can result in reduced tomato plant growth and that root gall production associated with root infection was not necessary for this retardation of growth response. This further suggests that possible yield impacts in other crop species that are hosts for S. subterranea root infection are worthy of examination.

Attempts at management of diseases caused by protozoan plant parasitic Phytomyxea have often been ineffective. The dormant life stage is characterised by long‐lived highly robust resting spores that are largely impervious to chemical treatment and environmental stress. This review explores some life stage weaknesses and highlights possible control measures associated with resting spore germination and zoospore taxis. With phytomyxid pathogens of agricultural importance, zoospore release from resting spores is stimulated by plant root exudates. On germination, the zoospores are attracted to host roots by chemoattractant components of root exudates. Both the relatively metabolically inactive resting spore and motile zoospore need to sense the chemical environment to determine the suitability of these germination stimulants or attractants respectively, before they can initiate an appropriate response. Blocking such sensing could inhibit resting spore germination or zoospore taxis. Conversely, the short life span and the vulnerability of zoospores to the environment require them to infect their host within a few hours after release. Identifying a mechanism or conditions that could synchronise resting spore germination in the absence of host plants could lead to diminished pathogen populations in the field.

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Ca2+ signaling regulates physiological processes including chemotaxis in eukaryotes and prokaryotes. Its inhibition has formed the basis for control of human disease but remains largely unexplored for plant disease. This study investigated the role of Ca2+ signaling on motility and chemotaxis of Spongospora subterranea zoospores, responsible for root infections leading to potato root and tuber disease. Cytosolic Ca2+ flux inhibition with Ca2+ antagonists were found to alter zoospore swimming patterns and constrain zoospore chemotaxis, root attachment and zoosporangia infection. LaCl3 and GdCl3, both Ca2+ channel blockers, at concentrations ≥ 50 μM showed complete inhibition of zoospore chemotaxis, root attachment and zoosporangia root infection. The Ca2+ chelator EGTA, showed efficient chemotaxis inhibition but had relatively less effect on root attachment. Conversely the calmodulin antagonist trifluoperazine had lesser effect on zoospore chemotaxis but showed strong inhibition of zoospore root attachment. Amiloride hydrochloride had a significant inhibitory effect on chemotaxis, root attachment, and zoosporangia root infection with dose rates ≥ 150 μM. As expected, zoospore attachment was directly associated with root infection and zoosporangia development. These results highlight the fundamental role of Ca2+ signaling in zoospore chemotaxis and disease establishment. Their efficient interruption may provide durable and practical control of Phytomyxea soilborne diseases in the field.

Spongospora subterranea, which causes powdery scab of potato, infects a diverse range of plant species. Crop rotation as a powdery scab management tool will be compromised if pathogen hosts exist between potato crops. Opium poppy (Papaver somniferum) and pyrethrum (Tanacetum cinerariifolium) are important crops within intensive vegetable production rotations in NW Tasmania. Measurements of S. subterranea soil inoculum within a commercial field showed pathogen amounts were substantially elevated following an opium poppy crop, which suggested host status. In glasshouse testing, opium poppy and pyrethrum were confirmed as hosts of S. subterranea, with opium poppy the more susceptible of the two. Both species were less susceptible than tomato, a known host. Observations of early growth suggested inoculation impacts on all three plant species, although at 16 (tomato and opium poppy) or 26 (pyrethrum) weeks postinoculation, only tomato had significantly reduced shoot and root development. The role of rotation crops in inoculum persistence and the possible role of S. subterranea as a minor pathogen of nonpotato crops are discussed.

Spongospora subterranea f. sp. subterranea is an important pathogen of potato responsible for major losses in most potato growing regions of the world. Infection is initiated by bi-flagellated motile zoospores released from long-lived resting spores. Zoospore chemotaxis to the host plant root is widely believed to be stimulated by host root exudate compounds, although direct evidence is lacking. This study refined the traditional chemotaxis capillary assay. With this we provided the first empirical evidence of S. subterranea zoospore chemotaxis. Individual potato root exudate metabolites were either taxis neutral, inhibitory, or attractant to the zoospores. L-glutamine was the strongest chemoattractant, while spermine was the most inhibitory. Zoospore motility and chemotaxis were constrained by strongly acidic or alkaline solutions of pH < 5.3 and > 8.5, respectively. Beyond pH, ionic constituents of the test solution affected zoospore motility as Sorensen’s phosphate buffer stalled zoospore motility, but HEPES buffer at the same concentration and pH had little or no negative motility effect. Zoospore motility, as characterized by several parameters, influenced chemotaxis. Among the parameters measured, total distance travelled was the best predictor of zoospore chemotaxis. The characterization of environmental and ecological effects on zoospore motility and chemotaxis highlights useful targets for S. subterranea disease control through manipulation of zoospore taxis or selection of host resistance traits.

Misidentification of Aframomum melegueta, an important medicinal plant has huge adverse health implications. Thus, the scientific description and characterization of the accessions in Ghana was imperative. The study found the plant to bear creepy stolons which bear terminal bud for production of tillers instead of rhizomes which had earlier been reported by other investigators. All the accessions had a distinctive non storage bulbous structure at the base of the pseudostem. The UPGMA dendrogram clustered the accession into Ashanti and Eastern accessions based on ecological location. The Eastern accessions were sub-clustered in two groups based on fruit colour.