The host range ofSpongospora subterranea f. sp.subterranea in the United States

This study was performed to determine the host range ofSpongospora subterranea f. sp.subterranea on common crops and weeds in the northeastern United States. Seedlings of the plants were grown in nutrient solutions and inoculated with spore balls ofS. subterranea. The roots were microscopically examined for the presence of plasmodia or zoosporangia 14 days after inoculation. The plants were then transferred to a greenhouse and grown in a soilless mix. The roots were examined for the presence of symptoms and spore balls after 4 months. Of 26 species within 10 families from monocotyledons and dicotyledons tested, 16 species were found to be susceptible toS. subterranea. Twelve species were newly recorded hosts forS. subterranea. Gall symptoms were observed on the roots of six species and spore balls were found on three species. Evidence is presented for the first time that galls and spore balls ofS. subterranea might form on non-Solanaceous species. This investigation is important for the cultural management of potato powdery scab disease because there currently are no effective controls.     

Potato powdery scab, caused bySpongospora subterranea f. sp.subterranea, in Costa Rica

Summary Seven samples of potato powdery scab like-lesions were used to determine and confirm the occurrence ofSpongospora subterranea f.sp.subterranea in Costa Rica. Light microscope observations of spore balls and zoosporangia in tomato bait plants identified the organism asS. subterranea. Positive DAS-ELISA test results from all seven samples and PCR specific amplification products from five samples confirmed its identity. The geographical location of the samples source plantations suggests wide distribution of the plant pathogen across Costa Rica main potato growing areas. Different lesion types may indicate host-pathogen or environment-pathogen interactions. The symptoms differences and PCR amplification results among specific primer pairs suggest that some degree of genetic variation among theS. subterranea samples may exist; however, further testing is required.     

Improved diagnosis of powdery scab (Spongospora subterranea f.sp.subterranea) symptoms on potato tubers (Solanum tuberosum L.)

Summary Based on visual inspection, discrimination between common scab (Streptomyces spp.) and powdery scab (Spongospora subterranea) can be difficult. Inspections are performed on unwashed samples, incidentally supported by microscopic examination. During 1994–1996 surveys were performed in The Netherlands on tubers with symptoms resembling common scab. Under microscopic assessment nearly all samples showed the presence of structures resembling cystosori (sporeballs) ofS. subterranea. At that time confirmation using alternative techniques was not possible. In 2003 research was undertaken to clarify the situation with respect to scab on potato tubers in The Netherlands. One hundred and eighteen scab samples were extensively tested forS. subterranea. All samples were digitally photographed, microscopically examinated and tested with real-time PCR and DAS-ELISA. Use of these modern methods resulted in a clear picture of symptoms that can be attributed toS. subterranea. A lot of scab samples with structures resembling cystosori could not be confirmed as contaminated withS. subterranea.     

Genetic variation and phylogeny ofSpongospora subterranea f.sp.subterranea based on ribosomal DNA sequence analysis

The nuclear rDNA regions of the two internal transcribed spacers (ITS1 and ITS2) and 5.8S rRNA gene from 52 field isolates ofSpongospora subterranea f.sp.subterranea obtained from the British Isles and North America were polymerase chain reaction-amplified, sequenced, and assessed for genetic variation. Two genetically distinct groups (I and II) were identified based on the ITS sequence diversity among the isolates, representing 34.6% and 65.4% of the isolates, respectively. British Isles isolates occurred in groups I and II, whereas North American isolates belonged only to group II. The British Isles groups ofS. subterranea were associated with particular potato cultivars. The full-length small-subunit rRNA gene ofS. subterranea was sequenced and analyzed by both neighbor-joining and parsimony methods to clarify the taxonomic position of this pathogen. The results of phylogenetic analysis showed thatS. subterranea grouped together with other species of plasmodiphorids, and this group clustered with the phylum Cercozoa, an assemblage of filose and reticulose amoebae and phylogenetically related zooflagellates. The recognition of the existence of different genetic groups withinS. subterranea will be important for the design of plant-breeding programs and in testing for plant resistance.     

Alternative hosts for potato mop-top virus, genus Pomovirus and its vectorSpongospora subterranea f.sp. subterranea

Summary Seventeen weed species common in the potato fields in Denmark were grown in a hydroponic system infested with viruliferous zoospores ofSpongospora subterranea f.sp.subterranea carrying potato mop-top virus (PMTV). The plants were examined for infection with PMTV andS.s.s. using DAS-ELISA and based on visible symptoms. Only two weed species were found to be infected with PMTV,Chenopodium album andSolanum nigrum, whereas 13 became infected withS.s.s. C. album was infected with PMTV by mechanical inoculation were the infection became systemically and the leaves showed necrotic spots.S. nigrum became local infected with PMTV by mechanical inoculation. By inoculation with viruliferousS.s.s. the roots ofS. nigrum became infected but in three weeks PMTV had not spread into the top of the plants.Nicotiana benthamiana was used as a control susceptible toS.s.s. and PMTV.     

Resistance toSpongospora subterranea in tuber-bearing and non tuber-bearingSolanum spp.

Summary The incidence of infection withSpongospora subterranea was studied in the non tuber-bearingSolanum brevidens andS. etuberosum and the tuber-bearingS. acaule, S. sucrense andS. tuberosum cvs Olympia and Pito. Shoot cuttings were grown in soil naturally infested withS. subterranea, or the roots were inoculated with a zoospore suspension. Logit models were used to analyse the data. The incidence ofS. subterranea was higher in plants inoculated with zoospore suspension than in those grown in infested soil (odds ratio (OR) 10.65). Ageing the inoculum reduced the incidence of infection in the plants (OR 0.30) without altering the interspecific differences. The ORs of infection (compared to cv. Olympia) were 0.07, 0.29, 0.60 and 2.88 forS. acaule, S. sucrense, S. brevidens andS. etuberosum. OnlyS. acaule was significantly more resistant to infection than cv. Olympia. No infection was detected in cv. Pito.     

Chloropicrin Soil Fumigation Reduces <Emphasis Type="Italic">Spongospora subterranea</Emphasis> Soil Inoculum Levels but Does Not Control Powdery Scab Disease on Roots and Tubers of Potato

The effect of chloropicrin fumigation on the soil populations of Spongospora subterranea and the development of powdery scab, formation of root galls and tuber yield was investigated in seven field trials conducted in Minnesota and North Dakota. Sixteen potato cultivars, with different levels of susceptibility to disease on roots and tubers, were planted in plots treated with chloropicrin at rates ranging from zero to 201.8 kg a.i. ha^?1. The amount of S. subterranea DNA in soil was determined using qPCR. Bioassays were conducted to further assess the effect of chloropicrin fumigation on root colonization by S. subterranea in two potato cultivars with contrasting disease susceptibility. In the field, chloropicrin applied at rates between 70.1 to 201.8 kg a.i. ha^?1 significantly decreased S. subterranea initial inoculum in soil but increased the amount of disease observed on roots and tubers of susceptible cultivars. The effect of increasing disease was confirmed in controlled conditions experiments. Although the amount of S. subterranea DNA in roots of bioassay plants increased with increasing chloropicrin rates, it remained similar among potato cultivars. Chloropicrin fumigation significantly increased tuber yield which in cultivars such as Shepody and Umatilla Russet were associated with the amount root galls (r = 0.30; P < 0.03). Results of these studies contradict earlier reports on the use of chloropicrin fumigation for the control of powdery scab. Factors other than inoculum level, such as environmental conditions that affect inoculum efficiency and host susceptibility, may be significant contributors to the development of powdery scab and root gall formation.     

Assessing the resistance of potatoes to powdery scab (Spongospora subterranea (Wallr.) Lagerh.)

Summary The reaction of nine cultivars to infection bySpongospora subterranea (powdery scab) was studied in two successive years of trials in naturally infested field soil and in artificially-inoculated field soil contained in brick-sided beds. The incidence of infection was recorded on a 1–9 scale, with complete absence of the disease scoring 9. The correlation coefficient (r) between scores from bed and field was 0.84 (1985) and 0.81 (1986). The field test gave satisfactory discrimination between resistant and susceptible cultivars in only one year, but the bed test gave good results in both years and is suggested as a small-scale alternative to field trials for this disease.     

Effect of planting date and inoculum level on incidence and severity of powdery scab on potato

Summary Powdery scab incidence and severity was examined on six potato cultivars planted at two different dates in a naturally infested field. There were two sub-plots; one where seed was exposed prior to planting to spores ofSpongospora subterranea from scabby peels, which were then added to the furrow at planting, and another where seed was exposed only to natural inoculum within the field. The later planting data reduced incidence and severity, but there were no differences between sub-plots. All cultivars became infected, but ‘Rosa’ was the most susceptible and ‘Katahdin’ the most resistant. Contribution No. 1720, Department of Plant Pathology, The Pennsylvania Agricultural Experiment Station. Authorized for publication September 22, 1988 as Journal Series Paper No. 8007.     

Incidence and severity of powdery scab on potatoes in Pennsylvania

Studies were conducted in Potter Co., Pennsylvania to investigate the effect of powdery scab (Spongospora subterranea) on five potato cultivars (Norchip, Rosa, Kennebec, Katahdin, and Monona) at two planting dates. Soil temperature was within the range of 15–18 C and soil moisture was within 15–19% based on dry weight throughout the season. The effect of planting date was significant at each disease assessment, except for the severity on the fourth assessment. By the end of the season, incidence of scab was 66% or more for all cultivars. Rosa, Kennebec and Katahdin had a greater scab incidence over both planting dates and a greater severity at the first planting date than Monona and Norchip.     

马铃薯粉痂菌诱饵植物筛选及环境对病害发生的影响

通过筛选获得土壤中马铃薯粉痂菌的诱饵植物,明确不同地区土样的含菌量以及马铃薯栽培品种对土壤含菌量的影响;同时,研究温度和土壤含水量对马铃薯粉痂病发病情况的影响。采用带菌土壤诱导和带菌薯块诱导两种活体诱导的方法进行马铃薯粉痂菌的诱导;在温室条件下设计不同的处理来研究温度和土壤含水量对马铃薯粉痂病发病的影响。筛选得到诱饵植物为番茄品种‘3-375’,不同地区和种植不同马铃薯品种的土壤中粉痂菌的含量存在差异。温度和土壤含水量对粉痂病发病情况有一定影响。土壤中存在马铃薯粉痂菌,该病原菌可以通过土壤和种薯传播;温度和土壤含水量等环境因素对该病害的发生有影响。     

Relationship Between Tuber Storage Proteins and Tuber Powdery Scab Resistance in Potato

The potato genotypes (Solanum tuberosum L.) with russet tuber skin are generally resistant to powdery scab (Spongospora subterranea f.sp. subterranea or Sss). Lipoxygenase (LOX; EC 1.13.11.12) and patatin are two key storage proteins that are known to offer resistance to several diseases and insects. The objective of this study was to find out the relationship of these proteins in stored tubers with potato tuber powdery scab resistance, especially in russet skinned potatoes. An evaluation of potato germplasm with different tuber characteristics in a greenhouse environment over several years (2006–’11) suggests that russet skinned tuber genotypes (Mesa Russet, Centennial Russet and Russet Nugget) with negligible tuber disease severity index (DSI) and 100 % marketability were resistant to powdery scab. Higher physiological levels of LOX protein (on a dry weight basis) were negatively correlated with tuber DSI and positively correlated with tuber russet skin. Tuber total protein and patatin-lipase levels did not have a significant relationship with tuber powdery scab resistance. The proposed role of LOX protein in suberin- and/or non-suberin-mediated mechanisms of powdery scab resistance in russet skinned tubers are discussed here. The physiological levels of LOX protein can be considered as a useful marker for powdery scab resistance in potato breeding programs.     

Effects of Different Soil Treatments on the Development of <Emphasis Type="Italic">Spongospora subterranea</Emphasis> f. sp. <Emphasis Type="Italic">subterranea</Emphasis> in Potato Roots and Tubers in the Greenhouse

Powdery scab caused by Spongospora subterranea f. sp. subterranea (Sss) causes extensive losses in potato production systems globally. Two pot experiments were established in the greenhouse in summer 2013 and winter 2014 to evaluate the effectiveness of different soil chemicals, fumigant, amendments and biological control agents (BCAs) against Sss in the rhizospheric soil, potato roots and tubers. The study used visual assessment methods to assess the effect of treatments on root galling and zoosporangia production, and qPCR to measure Sss concentration in the soil and in the potato roots and tubers. All six soil treatments, namely metam sodium, fluazinam, ZincMax, calcium cyanamide, Biocult and a combination of Bacillus subtilis and Trichoderma asperellum recorded significantly (P < 0.05) lower numbers of zoosporangia in the roots compared to the untreated control. The same effect was observed on the concentration of Sss DNA in the roots at tuber initiation. A more diverse picture was obtained when root gall scores at tuber initiation and Sss DNA in the rhizospheric soil at tuber initiation and harvesting were compared. Significant differences (P < 0.05) were also noted in disease severity, disease incidence, and tuber yield between metam sodium, fluazinam, ZincMax, calcium cyanamide and the untreated control. Calcium cyanamide gave the highest tuber yield. The study demonstrated the potential of soil treatments such as metam sodium, fluazinam, ZincMax and calcium cyanamide in managing Sss in potatoes by reducing the pathogen both in the rhizospheric soil and the roots of the potato plant.     

Incidence, appearance and development of potato mop-top furovirus-induced spraing in potato cultivars and the influence on yield, distribution in Denmark and detection of the virus in tubers by ELISA

Summary 23 potato cultivars were grown in fields infested with potato mop-top virus and spraing was assessed on tubers at harvest and after storage. Large differences in spraing susceptibility were found between cultivars. Compared with other countries, spraing in Denmark is characterised by a high incidence at harvest, a low increase during storage and a very low proportion of superficial spraing. Decrease in spraing during storage was recorded in two cultivars. DASELISA tests for PMTV in tubers revealted a high reliability. Mapping of PMTV in important Danish potato growing areas showed that the virus is widespread. Occurrence of spraing did not influence total yield or dry matter content. Soil acidity did not influence incidence of spraing but it was more common on coarse-grained soil than on finer sandy soils. PMTV in viruliferous resting spores ofSpongospora subterranea was inactivated by heating to 90°C for 15 minutes.     

Review: Powdery Scab of Potato—Increased Knowledge of Pathogen Biology and Disease Epidemiology for Effective Disease Management

The importance of the potato tuber disease powdery scab, caused by the zoosporic pathogen Spongospora subterranea f. sp. subterranea, has increased worldwide, and the disease is one of the most important problems facing potato production in some regions. This soilborne pathogen produces many resting spores which can remain dormant for long periods, are highly resistant to environmental stresses and can spread the disease on seed potatoes and in contaminated soil. The enigmatic nature of this organism exacerbates the development of effective powdery scab control methods. Substantial knowledge has been gained in the last decade on the biology of the pathogen and the epidemiology of the disease, but no single effective control measure is, or is likely to be, available. An integrated approach to powdery scab management is the aim, with host resistance as a substantial and sustainable component. Further research on the epidemiology of powdery scab and population genetics of the pathogen is urgently required. All stakeholders involved in the potato industry must become aware that solution of the powdery scab problem is likely to be a long-term goal. When resistant cultivars with all the other characteristics demanded for marketing high-quality potatoes are available, and when disease risk from the pathogen on seed and/or in soil can be accurately determined, then the mission to develop effective powdery scab control will become achievable.     

Occurrence of Skin Blemish Diseases (Scab and Scurf) in Norwegian Potato Production

A survey of the prevalence of skin blemish diseases in potatoes after the growing seasons of 2008 and 2009 was carried out on 247 potato lots representing different cultivars and production regions in Norway. The results showed the presence of silver scurf (Helminthosporium solani) in all lots. Skin spot (Polyscytalum pustulans) and black scurf (Rhizoctonia solani) were found in 80% of the lots, and black dot (Colletotrichum coccodes) and common scab caused by Streptomyces spp. were present in 50–70%. Also, powdery scab (Spongospora subterranea) occurred in 65–80% of the lots, and root-lesion nematodes (Pratylenchus spp.) were detected in 60% of the sub-samples that exhibited symptoms of common scab.     

Evaluation of some North and South American potato breeding lines for resistance toPotato mop-top virus in Sweden

The necrotic symptoms (spraing) in tubers caused byPotato mop-top pomovirus (PMTV) have become a severe problem for potato production in Scandinavia. PMTV is transmitted by the powdery scab pathogen (Spongospora subterranea) and no methods for control are currently available. Two breeding lines (NY99 and NY103) from the Cornell University potato breeding program, twotuberosum ×acaule lines (TA3.8.3.3 and TA3.5.3.7) from the International Potato Center (CIP), and one line (IvP35) ofSolarium phureja were tested for resistance to PMTV in field trials in Sweden in 1998 and 1999. In both years, NY99 had a low incidence of PMTV infection in tubers, and the infected tubers showed a low accumulation of PMTV, indicating that NY99 is a promising new source of resistance to PMTV for breeding programs. Furthermore, it may be suitable for cultivation in Scandinavia, which, however, needs to be evaluated in more extensive field trials.     

Effects of inoculum density and cultivar resistance on common scab of potato and population dynamics ofStreptomyces scabies

The interaction ofStreptomyces scabies, causal agent of common scab, and its potato host was examined under scab-conducive conditions in the greenhouse. Three potato cultivars with different levels of resistance to common scab were inoculated with four levels of two rifampin-resistant strains ofS. scabies. In general, scab severity increased linearly with an increase in log₁₀ of the inoculum, but both cultivar resistance and strain ofS. scabies affected the slope of the regression line. Rhizosphere and rhizoplane populations ofS. scabies also increased with increasing soil population. One strain ofS. scabies consistently had higher rhizosphere and rhizoplane populations than the other strain. However, rhizosphere population was not consistently related to scab severity, scab incidence, cultivar resistance, or strain virulence.     

QuantifyingVerticillium dahliae in soils collected from potato fields using a competitive PCR assay

A quantitative PCR assay based on the competitive PCR technique was compared to the classical soil dilution (SD) method for its ability to estimateV. dahliae propagules directly in soils collected from fields under potato production. A strong correlation (r = 0.97) was observed betweenV. dahliae propagules estimated using the quantitative PCR assay and those using the SD method. Coamplification ofV. dahliae DNA with competitor DNA provided accurate quantification in the range of 10² to 10⁷ spores and 1 to 100 microsclerotia/g of soil. The number ofV. dahliae propagules detected in PEI soils ranged from 4.9 to 15.6 and 0.06 to 0.5 microsclerotia/g of soil for PCR assay and SD method, respectively. The strong correlation between PCR assay and SD method and the non significant differences between replications of PCR estimates ofV. dahliae propagules in soils (P< 0.05) show that the PCR assay is reliable and reproducible, and comparable to the SD method. This method is fast, does not depend on the subjectiveness of the traditional plating method, and offers an improvement in speed and precision over currently used methods. In addition, it can be extended to estimateV. dahliae propagules in other pathosystems and finds immediate and practical use in epidemiological studies to determine the effects of various crop management strategies on the dynamics and level of fungal propagules in the soil in order to establish threshold levels for assessing disease risks and develop disease prediction systems.     

Reaction of potato varieties toPotato mop-top virus infection in the andes

The unexpected detection ofPotato mop-top virus (PMTV) in potatoes growing at several locations in the U.S.A. and Canada in 2002 has led to the realization that this soil-borne virus may be widespread throughout the potato-producing regions of both countries. A lack of information concerning the response of U.S. cultivars to PMTV infection caused us to examine the effects of PMTV on field-grown plants at three locations in the Peruvian Andes where the virus and its fungal vector,Spongospora subterranea, are endemic. All 21 U.S. cultivars tested proved susceptible to PMTV infection, especially at La Victoria where the overall incidence of both PMTV and powdery scab was high. Symptom expression in the foliage proved to be an unreliable indicator of virus infection, and thus, more reliable serological (NCM-ELISA) and nucleic acid-based techniques (NASH and RT-PCR) were used to monitor tuber tissue for the presence of PMTV. As much as 25% of field-grown tubers of cvs Kennebec, Monona, and Norland were infected with PMTV, but no correlation between virus infection and either the incidence or severity of powdery scab for any variety was apparent. Although PMTV infection did not result in the appearance of spraing or other internal necrotic reactions resembling those reported from many North American and European locations, a disproportionate proportion of infected tubers did exhibit a reticulate surface cracking. In hydroponic culture, the proportion of cracked tubers increased dramatically when the nutrient solution was seeded with virus-infestedS. subterranea. Comparatively few tubers of cvs Monona and Russet Burbank exhibited this surface cracking, suggesting that these two varieties may be somewhat tolerant to PMTV infection.