Powdery Scab of Potato—Occurrence, Life Cycle and Epidemiology

Powdery scab of potato, caused by the zoosporic pathogen Spongospora subterranea f.sp. subterranea (Sss), is an often underestimated disease, which has lead to lack of appropriate control strategies. A new wave of increasing importance of this disease has occurred in the last 30years in many countries, among them France, Pakistan, Japan, Australia, New Zealand, Costa Rica, USA, and, very recently, Colombia, Korea and China. A consequence is that occurrence of, and research on, powdery scab has shown a cyclic pattern. Additionally to its importance as a pathogen, Sss is a vector of potato mop top virus which itself can cause substantial damage. Factors such as intensification of potato production, increasing use of susceptible cultivars, more frequent irrigation and banning of mercury, previously used as an efficient seed tuber treatment, have all contributed to greater incidence of powdery scab. Since 1842, when Wallroth first described the disease in the scientific literature, many researchers, particularly before 1960, started to work with Sss, mostly because powdery scab became a problem in their respective countries. Today we know many aspects of the biology of the biotrophic protozoan organism that causes powdery scab, but we still lack basic knowledge on the etiology and epidemiology of the disease. We lack sufficient knowledge of the factors that affect survival of the resting structures, potato and alternative host infection and disease development. This knowledge is essential in predicting disease risk and developing effective powdery scab management strategie

Morphological Enumeration of Resting Spores in Sporosori of the Plant Pathogen Spongospora subterranean

Plasmodiophorid sporosori (aggregations of resting spores) reach their most complex form in Spongospora subterranea f. sp. subterranea, the biotrophic plant pathogen which causes the economically important disease powdery scab of potato (Solanum tuberosum). Resting spores are the perennation life cycle stage of plasmodiophorids, allowing them to survive for long periods and infect subsequent host generations. Light microscopy was used to measure resting spores and sporosori of Sp. subterranea, and enumerate resting spores in individual sporosori. Mean resting spore diameters differed for two sporosorus collections, being 4.0 μm (from New Zealand) and 4.3 μm (from Switzerland). Counts of resting spores in 4 μm thick serial sections of sporosori from one collection gave a mean of 667 (range 155 to 1,526) resting spores per sporosorus. Number of resting spores per sporosorus was closely related to sporosorus volume, and could be accurately estimated using the formula; number of resting spores = 0.0081 × sporosorus volume (assuming sporosori to be spheroids). Using this formula, mean numbers of resting spores in sporosori from 37 Sp. subterranea collections from field-grown potato tubers from 13 countries were determined to range from 199 to 713. Differences in numbers of resting spores between the collections were statistically significant (P < 0.05), and independent of country or host cultivar of origin, indicating that enumeration should be carried out for individual sporosorus collections to accurately quantify inoculum. Morphology, using scanning electron microscopy, also showed that between 2 and 51% (average 20%) of resting spores released zoospores after exposure to roots of host plants. The formula for resting spore enumeration validated in this study can be used to standardise Sp. subterranea resting spore inoculum for plant pathology studies, and possibly to assist determination of soil inoculum potential for disease risk evaluations

Powdery scab of potato - occurrence, life cycle and epidemiology

ISSN:1874-9380ISSN:0003-0589ISSN:1099-209

Infection Risk Potential of South American Spongospora subterranea f.sp. subterranea Root Gall and Tuber Lesion Inoculum on Potato ( Solanum tuberosum ssp. tuberosum )

Spongospora subterranea f. sp. subterranea causes the potato diseases powdery scab on tubers and galls on roots, and occurs in most potato production areas worldwide. The pathogen was probably introduced to Europe from South America in the 16th century. Three different genotype clusters have been found worldwide: the genetically variable groups from South America (native), and, in contrast, the nearly clonal group outside South America (invasive). An inoculation experiment was carried out with the long-day potato host ‘Agria' comparing three different native Spongospora resting spore inocula with an invasive one, to determine the infection risk potential on a widely grown potato subspecies. All inocula led to root infection. Invasive tuber lesion sporosori from ‘Agria' produced the greatest amount of infection, whereas the tuber lesion inoculum from the Venezuelan S. tuberosum ssp. tuberosum host and the root gall inoculum from the Colombian S. phureja host caused the least infections. The inoculum genotypes corresponded to all of the three previously described groups. Most root galls showed the invasive group type, independent of the inoculum. These results suggest that the most successful invasive genotype is still present in native pathogen populations and emphasize the need for continued quarantine vigilance to prevent new virulent recombinants of the pathogen

Evaluation of the Sss AgriStrip rapid diagnostic test for the detectionof Spongospora subterranea on potato tubers

International audienceSpongospora subterranea, f.sp. subterranea (Sss), which causes powdery scab, is mainly spread through infected seed tubers and survives in contaminated soil for many years. The visual assessment of tuber lots by inspectors carries the risk of misidentification due to the difficulty of distinguishing lesions caused by either Sss or Streptomyces spp.. To avoid this, the "Sss AgriStrip", a rapid and lab-independent test tool based on a lateral flow immunoassay has been developed, and we assessed its accuracy and sensitivity for detecting Sss. The Sss AgriStrip performed as well as other lab-based identification methods. The Sss AgriStrip, microscopy, ELISA, PCR, and real-time PCR techniques identified infection with S. subterranea in all tubers with typical powdery scab lesions. When lots with tubers showing a mixture of typical and atypical (suspicious) symptoms were tested, the presence of S. subterranea was confirmed in all lesions by all methods. The DNA content was generally lower in atypical than in typical lesions. Diverse and suspicious symptoms, which were difficult to assign to either powdery or common scab, tested negative with Sss AgriStrip and the other methods. This was despite microscopic observation of sporosori-like structures in some samples. Isolation and molecular identification confirmed that these lesions were mostly caused by Streptomyces spp. The Sss AgriStrip is as sensitive as DAS-ELISA with a detection limit between 1 and 10 sporosori per ml buffer. It is ideal for rapid and selective detection of Sss on farms and border inspection points to prevent spread of the pathogen

Powdery scab effect on the potato Solanum tuberosum ssp andigena growth and yield

Powdery scab affects most potato production zones in the world. The causal organism Spongospora subterranea f. sp. subterranea forms galls in roots and lesions on tubers during its replication. Recent researches suggest that S. subterranea could cause harmful effects on the host plant and potentially on yield.In order to quantify the disease impact on plant growth and yield, potato Solanum tuberosum ssp. andigena, cv. Diacol Capiro was grown in a soil infested with S. subterranea and compared to a healthy control soil. Data was taken at the flowering stage and at harvest. S. subterranea caused a plant length reduction of 23%, a foliar dry weight reduction of 32% and a tuber weight reduction of 30%, whereas S. subterranea did not reduce the number of tubers or stems.ISSN:1982-5676ISSN:1983-205

Percutaneous ultrasound-guided abomasocentesis in cows

The goal of this study was to determine the optimal location for ultrasound-guided centesis of the bovine abomasum and to assess the safety of the procedure. In the first part of this study, the technique was applied to 50 clinically healthy cows which were slaughtered within two hours of the procedure. The abomasum and peritoneum were then examined for lesions. In all but one cow, the location for abomasocentesis was 10 to 27 cm caudal to the xiphoid and on the ventral midline or up to 10 cm to the right of it. No peritoneal lesions were observed in any of the cows. In all cases, the site of centesis was visible as a localised haemorrhage on the serosal surface of the abomasum. In 41 of the cows, a haematoma was visible on the mucosal surface of the abomasum. In the second part of the study, 10 cows were monitored clinically for 10 days after abomasocentesis, to assess the safety of the procedure. The appetite, general behaviour, attitude and rectal temperature of the cows remained normal. The haematocrit, total and differential leucocyte counts, and the concentrations of total solids and fibrinogen were determined daily and remained within their normal ranges. At slaughter minimal changes, such as localised reddening and adhesions between the site of the puncture in the abomasum and the abdominal wall, were visible in three of the cows

Powdery scab effect on the potato Solanum tuberosum ssp.andigena growth and yield: andigena

Powdery scab affects most potato production zones in the world. The causal organism Spongospora subterranea f. sp. subterranea forms galls in roots and lesions on tubers during its replication. Recent researches suggest that S. subterranea could cause harmful effects on the host plant and potentially on yield.In order to quantify the disease impact on plant growth and yield, potato Solanum tuberosum ssp. andigena, cv. Diacol Capiro was grown in a soil infested with S. subterranea and compared to a healthy control soil. Data was taken at the flowering stage and at harvest. S. subterranea caused a plant length reduction of 23%, a foliar dry weight reduction of 32% and a tuber weight reduction of 30%, whereas S. subterranea did not reduce the number of tubers or stems