Incidence Of Powdery Scab Research Articles

Effects of Silicon on Development and Controlling of Powdery Scab in Irish Potato (Solanum tuberosum)

Effects of different silicon levels on plant height, stem diameter, disease incidence and severity and its activity on polyphenol oxidase and peroxidase enzymes on powdery scab caused by Spongospora subterranean on Irish potatoes (BP1) was assessed. This was a greenhouse study at the University of Zimbabwe Crop Science department. A mixture of 50% sterilised vermiculite and 50% sterilised sand was used as growing media. 0, 250, 500 and 750ppm silicon concentrations were used. Irrigation water, other fertilizers and insecticides applied were made uniform across all treatments. Variations among treatments were monitored from three weeks after planting then on weekly basis for the coming eighty weeks. Silicon concentrations showed significance difference (p<0.001) on plant height and stem diameter of Irish potatoes. It proved to play a significant role in the growth of the potato plants. Silicon levels showed no significant difference on powdery scab incidence with all plants getting diseased. Silicon reduced the infestation severity at high concentrations. It also increased the activity of polyphenol oxidase and peroxidase enzymes in potatoes at different response rates. Results from the study indicates great potential of silicon based fertilizers in controlling powdery scab as well as growth rate of Irish potatoes.

Evaluation of Effects of Chemical Soil Treatments and Potato Cultivars on Spongospora subterranea Soil Inoculum and Incidence of Powdery Scab and Potato Mop-Top Virus in Potato.

Spongospora subterranea is a soilborne plasmodiophorid that causes powdery scab in potato. It also transmits potato mop-top virus (PMTV), which causes necrotic arcs (spraing) in potato tubers. Three field experiments were conducted in naturally S. subterranea-infested soil to investigate the effects of two chemicals, Omega 500F (fluazinam) and FOLI-R-PLUS RIDEZ (biological extract), on powdery scab, PMTV, and changes in S. subterranea inoculum with six different potato cultivars. The efficacy of soil treatment with these two chemicals on tuber lesions, root galling, and pathogen population was also assessed in greenhouse trials. The chemical treatments did not reduce powdery scab, root gall formation, or S. subterranea inoculum in the field or greenhouse trials. Postharvest S. subterranea soil inoculum in fields varied across farms and among potato cultivars but the pathogen population consistently increased by the end of the growing season. The evaluated russet cultivars were more tolerant to powdery scab than the yellow- or red-skinned cultivars but all were susceptible to PMTV. In the field, powdery scab indices and soil inoculum changes were positively correlated, while postharvest S. subterranea inoculum was positively correlated with root galling in both greenhouse trials. Powdery scab and PMTV occurred in noninoculated potting mix, indicating that peat-based potting mix is a source for both pathogens. These results demonstrate that chemical management methods currently used by farmers are ineffective, that S. subterranea and PMTV in potting mix can cause severe epidemics in greenhouses, and that potato cultivar choices impact inoculum increases in soil.

Control of potato powdery scab (Spongospora subterranea) in Israel with chloropicrin, metam sodium or fluazinam

Powdery scab, caused by Spongospora subterranea, causes significant economic damage in potato production worldwide due to reduced quality and marketability of seed and ware tubers. Three field experiments were conducted in naturally infested soil during winter 2008, 2012 and 2013 to evaluate the efficacy of soil fumigation on powdery scab on tubers, root galling and the pathogen populations in soil. Soil fumigation with metam sodium (MS) or chloropicrin (PIC) was highly effective in controlling the disease under field conditions. Powdery scab incidence and severity on tubers were significantly reduced by MS applied at 219–222 L a.i. ha−1 by 66–98%. In application of PIC at 99–396 kg a.i. ha−1 followed with immediate plastic cover, disease incidence on tubers was significantly reduced by 56–90%, whereas, uncovered PIC treatments had a lower efficacy. Root galling was also affected by the fumigants and was significantly lower in MS and PIC treatments as compared to the control. In-furrow fluazinam treatments were less effective than the fumigants, with only 18–20% reduction in disease incidence on tubers. Pathogen levels in the soil, determined shortly after fumigation, were significantly lower than in the control. However, at the end of the growing season, they were increased to high levels with no significant differences among all treatments.

Field Evaluation of Potato Genotypes for Resistance to Powdery Scab on Tubers and Root Gall Formation Caused by Spongospora subterranea

Spongospora subterranea causes root galls and powdery scab on potato tubers (Solanum tuberosum L.). Host resistance represents an economically suitable and long term approach for the management of the disease; however, the relationship between root and tuber symptoms may vary across potato genotypes. To assess susceptibility differences among genotypes, 30 potato cultivars and 83 advanced clones with varying skin type (market class) were evaluated for powdery scab and root gall formation. Five field experiments were conducted during 2011 and 2012 on naturally infested soils in Minnesota and North Dakota. Differences among genotypes in the degree of susceptibility to tuber and root symptoms were observed (P < 0.001, n = 33 to 80). Higher powdery scab pressure (P < 0.001, n = 90) was observed in North Dakota locations across years. Environmental conditions influenced the formation of root galls and the expression of powdery scab, with greatest variability among white- and red-skinned genotypes. Under high disease pressure, the estimates of broad-sense heritability for powdery scab incidence and severity were 0.76 and 0.63, respectively. Across environments, russet-skinned genotypes resulted in less disease on tubers, but yielded similar levels of root galls as red-skinned genotypes. Tuber scab and root gall formation indices were significantly associated (r = 0.42, P < 0.001, n = 80); however, high levels of disease in roots were observed in genotypes ranked resistant to powdery scab. Cultivars Dakota Trailblazer, Dakota Russet and Karu ranked highly resistant, whereas Shepody, Kennebec and Red LaSoda were highly susceptible to both phases of the disease. Cultivar selection is highly recommended for disease management.

Effect of Soil Moisture Management on the Development of Potato mop-top virus-Induced Tuber Necrosis.

Potato mop-top virus (PMTV), transmitted by Spongospora subterranea f. sp. subterranea, the causal agent of powdery scab in potato, has become one of the most important tuber necrosis viruses in the United States. The virus has been confirmed in six major potato-producing states in the United States since its identification in 2003. Currently, no control methods are available for PMTV or its vector. A growth-chamber experiment was conducted to investigate the potential of using moisture regime adjustments to manage tuber necrosis caused by PMTV. Two commercial potato cultivars with varying levels of sensitivity to PMTV, 'Dakota Crisp' and 'Ivory Crisp', were grown in soil obtained from a PMTV-infested field. Over the course of the plant growth cycle, plants of each cultivar were subjected to moisture regimes of wet throughout (WT), wet early/dry late (WEDL), dry early/wet late (DEWL), and dry throughout (DT). Soil moisture levels of 90 and 60% field capacity were considered wet and dry, respectively, while early and late refer to first and last 50 days after planting, respectively. Results of visual assessment conducted 3 months after storage showed significant differences in root gall formation, powdery scab on tubers, and PMTV tuber necrosis among moisture regimes. Powdery scab incidence was significantly higher in the WT and DEWL regimes than WEDL and DT regimes. PMTV tuber necrosis incidence did not differ between the WT and DEWL or between DEWL and WEDL moisture regimes. However, PMTV tuber necrosis incidence was significantly higher in WT than under WEDL and DT regimes. The incidence of PMTV tuber necrosis was significantly lower in the DT regime than in the other three moisture regimes. Severity of PMTV tuber necrosis was significantly higher in the WT than the other regimes, which did not differ statistically among themselves. A significant interaction was found between cultivar and moisture regime on root gall formation, with the highest number of galls found on Ivory Crisp grown in the WT moisture regime. A significant correlation was found between powdery scab incidence on tubers and PMTV-induced tuber necrosis incidence. The results of this study provide useful basic information upon which further work can be built for formulating irrigation management schemes that have the potential of reducing the likelihood of powdery scab infection and PMTV-induced tuber necrosis development in potato.

Sensitivity of Potato Cultivars to Potato mop-top virus-Induced Tuber Necrosis.

Potato (Solanum tuberosum) cultivars representing four market classes were assessed for sensitivity to Potato mop-top virus (PMTV)-induced tuber necrosis in three separate trials in a field in North Dakota known to be infested with PMTV. Reverse-transcription polymerase chain reaction confirmed the presence of PMTV in randomly selected samples. Results of tuber necrosis assessments conducted during storage demonstrated that sensitivity to PMTV-induced tuber necrosis among cultivars follows a continuum of tolerant to sensitive. As a group, the russet-skinned cultivars had a lower incidence of tuber necrosis than red-, yellow-, and white-skinned cultivars. The incidence and severity of PMTV-induced tuber necrosis in trial 1 were significantly correlated with those parameters in trial 2 across years. Significant correlations also existed between the incidence of powdery scab on tubers and the incidence of PMTV-induced tuber necrosis in trial 1 across years. A significant correlation was also found between root gall numbers and powdery scab incidence and severity on tubers as well as PMTV-induced tuber necrosis incidence in trial 2. The results of this study provide growers with disease management options by avoiding cultivars highly sensitive to PMTV-induced tuber necrosis development and potentially replacing them with tolerant cultivars in the same market class. It is apparent from these studies that field assessments can be used for the development of PMTV-resistant germplasm for use in future breeding strategies.

Atributos Morfológicos de Tubérculos en Genotipos de Solanum Phureja Juz et Buk y su Relación con la Incidencia de la Sarna Polvosa

&lt;p&gt;El objetivo de este trabajo es determinar si existe relación entre las características morfológicas de genotipos de &lt;em&gt;Solanum phureja &lt;/em&gt;de la colección de trabajo de la Universidad Nacional de Colombia y la respuesta al ataque de la sarna polvosa en tubérculos. Se evaluaron 93 genotipos y de cada uno se cosecharon diez tubérculos en el municipio de La Unión (Ant). Se determinó la densidad y el área de las lenticelas, el grosor de la peridermis, el color y forma de los tubérculos. Los datos obtenidos se confrontaron con la información de la incidencia de la sarna polvosa en tubérculos, bajo condiciones de campo. Se encontró que existe una amplia variabilidad genética en la colección evaluada para todas las características morfológicas de tubérculos. Los tubérculos de color negro presentaron mayor densidad y área de lenticelas y el menor grosor de peridermis, mientras que los genotipos rojizos presentaron menores densidades y área de lenticelas y valores intermedios para el grosor de la peridermis. Por otro lado los tubérculos alargados presentan mayor densidad de lenticelas y menor grosor de peridermis, mientras que los tubérculos ovalados presentan el comportamiento contrario. Igualmente se encontró que los tubérculos redondos presentaron bajos valores de densidad de lenticelas y grosor de la peridermis. No se encontró relación entre las características morfológicas evaluadas y la incidencia de la sarna polvosa en campo.&lt;/p&gt;

Somaclonal selection in potato for resistance to common scab provides concurrent resistance to powdery scab

Variant somaclones of potato cultivar Russet Burbank, selected for resistance to common scab using in vitro cell selection techniques, were tested for resistance to powdery scab, another important disease of potato caused by Spongospora subterranea. This pathogen also invades roots, producing root galls. Most variants consistently showed increased resistance to powdery scab, both in field and glasshouse challenge, when compared to the parental cultivar, several significantly so. On average, the best variant reduced powdery scab incidence by 51% and severity (tuber surface coverage) by 64%. In contrast, no improvement in the extent of root infection and root galling was seen. These results suggest host interactions during root and tuber infection are distinct. Correlation analyses of disease indices amongst the selected variants showed no association between Sp. subterranea root infection and gall scores, nor between root infection and tuber disease severity. However, a weak positive association was found between root gall score and tuber disease, and a strong correlation between tuber disease incidence and severity scores. Interestingly, positive correlations were also found between the extent of powdery and common scab resistance expressed and both incidence and severity of these diseases within the variants, suggesting a common defence mechanism. The role of thaxtomin A in selecting for concurrent resistance to both diseases is discussed.

Low amounts of Spongospora subterranea sporosorus inoculum cause severe powdery scab, root galling and reduced water use in potato (Solanum tuberosum)

This study measured effects of Spongospora subterranea soil inoculum levels on disease of potato tubers and roots, determining relationships between amount of sporosorus inoculum at planting, and both root function during plant growth and powdery scab on tubers at harvest. In a series of shadehouse experiments, different amounts of inoculum were applied to soil before planting tubers in large pots, and effects on plant growth and powdery scab incidence and severity were determined. In a glasshouse experiment different amounts of inoculum were applied to plants growing in sand/nutrient solution culture, and effects on water use, plant parameters and intensity of S. subterranea root gall formation were measured. In the shadehouse experiments, as few as 25 sporosori mL-1 soil caused powdery scab on daughter tubers, and greater amounts of inoculum reduced plant productivity (tuber yields). In the glasshouse experiment, from one to ten sporosori g-1 sand reduced water use by plants and shoot and root dry weights, and caused severe root galling. No consistently strong relationship was found between amount of inoculum at planting and disease incidence or severity at harvest. These results highlight the ability of S. subterranea to cause disease on host plants from low amounts of inoculum when conditions favour disease development, and emphasise the potential for the pathogen to reduce plant growth and tuber yields. They also show that inoculum detection methods should detect low soil inoculum amounts if they are to be useful for powdery scab prediction.

Effect of temperature on the transmission of Potato mop‐top virus from seed tuber and by its vector, Spongospora subterranea

Potato mop‐top virus (PMTV) causes disease in both the growing plant and tubers (spraing) of potato and is transmitted by the plasmodiophorid Spongospora subterranea, the cause of powdery scab. The effect of temperature during plant growth on the transmission of PMTV from infected seed tubers and from infested growing media was investigated in a series of glasshouse experiments. Symptoms developed on foliage of plants derived from infected seed tubers but none developed when PMTV was transmitted by S. subterranea in soil. The incidence of foliar symptoms was greatest on plants grown at 12°C, less at 16°C, few at 20°C and absent at 24°C. The transmission of PMTV from infected seed tubers was not significantly affected by temperatures between 12 and 24°C, but when the virus was transmitted by S. subterranea, minimal tuber infection occurred at 24°C and no differences were recorded at temperatures between 12 and 20°C. The incidence of powdery scab on tubers was greatest at 12 and 16°C and very low at 20 and 24°C. However, the incidence and severity of root galling caused by S. subterranea, was greatest at 20 and very low at 24°C. The incidence of powdery scab was greater on tubers of plants derived from infected seed tubers grown in a fluctuating temperature regime of 12 h at 20°C followed by 24 h at 12°C than on those grown at a constant 20°C, whereas the incidence of tuber infection by PMTV and spraing was similar for both regimes. This demonstrates that infection of roots can occur at a higher temperature than that for powdery scab on tubers and that this root infection can enable the transmission of PMTV into the potato plant.

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 30 years 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 strategies.

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

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.

Resistance to powdery scab inSolanum tuberosum L.

Seedlings and named varieties of potatoes were planted in five-hill lots in soil infested with the powdery scab organism. Over a three year period, the incidence of powdery scab varied considerably. In all three years, however, the Kennebec variety, used as a check, showed considerable infection indicating it to be very susceptible to this disease. The data suggest that resistance or susceptibility to this disease is a matter of degree. Although it cannot be said that any of the seedlings or named varieties tested are especially resistant to powdery scab, most of them proved to be less susceptible than the Kennebec variety.