The effect of irrigation and nitrogen on powdery scab and yield of potatoes

Summary Powdery scab, caused by the fungusSpongospora subterranea, has developed in the Cappodocia region of Turkey because of changes in agronomic practices, such as excessive irrigation and nitrogen fertilizer use and growth of highly susceptible cultivars. The most suitable irrigation and nitrogen application levels were established to maintain powdery scab at minimum levels without affecting potato yield. Three irrigation levels were used in 1998 (673, 897, 1121 mm) and five in 1999 (329, 494, 658, 823, 987 mm). Nitrogen levels were applied 150, 300, 450, 600 kg N ha⁻¹. In 1998, least powdery scab occurred with 673 mm irrigation, which yielded 41 t ha⁻¹ potatoes. The lowest disease severity occurred in 1999 with 494 mm irrigation and 150 kg N ha⁻¹. At these levels, tuber yield was 34 t ha⁻¹ which was not significantly different from the highest yield measured. In 1999 and at two of the three irrigation levels inl998, nitrogen increased disease severity.     

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.     

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.     

The cause of deep-pitted scab of potatoes

By use of a tyrosine-casinate-nitrate medium,Streptomyces atroolivaceous, S. cinerochromogenes, S. corchorusii, S. diastatochromogenes, S. lydicus, S. malachiticus, and three unidentifiedStreptomyces spp. were isolated from deep-pitted scab lesions on potato cultivars Green Mountain, Red Pontiac, Russet Burbank, and Saco. Over 90% of the deep-pitted lesions contained one or more of theseStreptomyces spp., butS. scabies the cause of shallow scab was not isolated. Isolates ofStreptomyces spp. were also consistently isolated from aseptically excised non-necrotic tissue near the edge of lesions. TheseStreptomyces spp. appeared to be the primary colonizers of this tissue. Alternaria spp.,Fusarium spp.,Penicillium spp.,Rhizopus spp.,Trichoderma spp., and several unidentified non-sporulating fungi as well asBacillus spp.,Pseudomonas spp., andMicrococcus spp. were isolated from deep-pitted scab lesions. Fungal and bacterial isolates varied from one scab lesion to another and except for anAlternaria sp., were not pathogenic. Most of theStreptomyces spp. isolates used to infest heat pasteurized field soil caused deep and/or shallow scab on tubers of the potato cultivar Kennebec in greenhouse and outdoor plantings. Re-isolations from resulting scab lesions yieldedStreptomyces spp. similar in morphology to those used as inoculum. We concluded that a number ofStreptomyces spp. probably includingS. scabies (ATCC 3352 = S.griseus) may cause deep and shallow scab.     

Resistance to powdery scab of seedling progenies ofSolanum tuberosum

Summary Tubers from individual seedlings of nineteen progenies involving eleven parental cultivars were tested for resistance to powdery scab over 2 years in artificially infested soil beds. There was a significant correlation between the mean resistance of a progeny and the phenotypic resistance of its parents.     

Incidence and tuber transmission of silver-scurf on potatoes in Israel

Summary Silver-scurf spots were observed during quarantine inspection from 1951–1959 among imported seed potatoes on their arrival in Israel. In 1960, the incidence of silver-scurf-affected tubers was especially common in cvs. Up-to-Date and Ulster Dale. Silver-scurf was frequent among tubers produced from above-mentioned seed, andHelminthosporium solani Dur. & Mont. was identified on samples from imported and local seeds. Transmission from parent set to daughter tubers was observed. Affected tubers produced either: a) hills with completely unaffected yield (Up-to-Date 25–91%, Ulster Dale 0–80%, Avenir 60%, Alpha 0%); b. partially affected hills; or c. completely affected hills (very small percentage in the yield plots and in sterile soil with the exception of Alpha with 70%). Most of the affected tubers were from partially affected hills. The keeping quality of affected tubers and the incidence in various cultivars were described.

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Zusammenfassung 1960 zeigten zertifizierte Pflanzkartoffeln aus Irland einen h?heren Befall an Silberschorf als üblich. Bei den befallenen Knollen handelt es sich um die Sorten Up-to-Date und Ulster Dale.Helminthosporium solani Dur. & Mont. wurde an Mustern von importiertem und von lokalem Pflanzgut festgestellt. Die Uebertragung von befallenen Mutterknollen auf die Tochterknollen wurde untersucht. Befallene Knollen erzeugten entweder Pflanzen mit vollst?ndig befallsfreien Knollen (Up-to-Date 25–91%, Ulster Dale 0–80%, Avenir 60%, Alpha 0%) oder Pflanzen mit teilweise befallenen oder vollst?ndig befallenen Knollen (Tabelle 1). Es gab keinen Hinweis dafür, dass infizierte Mutterknollen den Ertrag je Pflanze reduzieren. Der Befall an Knollen verschiedener Gr?ssen war ?hnlich (Tabelle 2). Lagerungsf?higkeit. Nach der Lagerung waren die befallenen Knollen st?rker geschrumpft als die nicht befallenen. Bei Kühllagerung war diese Erscheinung st?rker ausgepr?gt (Tabelle 3), aber weder hatte der Befall zugenommen, noch waren die Silberschorfflecken gr?sser geworden. Bei normaler Lagerung kam eine Vergr?sserung von Silberschorfflecken an anscheinend nicht befallenen Knollen nur vor, wenn die Knollen von teilweise befallenen Pflanzen stammten und an befallenen Knollen, die von Januar bis April eingelagert waren. Das Auftreten von Silberschorf an importierten anerkannten Pflanzkartoffeln wird beschrieben (Tabelle 4). Der Befall von sogenanntem lokalen Nachbau aus importiertem Pflanzgut war wie folgt gekennzeichnet: die meisten der befallenen Knollen stammten von teilweise befallenen Klonen, und sehr wenige Klone waren total befallen (Tabelle 5). Bei Up-to-Date waren die am st?rksten befallenen Knollen jene, die von importiertem Pflanzgut stammten (Holland, Schottland und D?nemark). Beim sogenannten lokalen Nachbau war der Befall sehr schwach, und er nahm noch ab, je ?fter das Pflanzgut in Israel nachgebaut wurde (Tabelle 6), und es bestand auch ein Unterschied zwischen dem Pflanzgut der drei Anbauperioden (Tabelle 7). Das Auftreten von Silberschorf bei verschiedenen Sorten wird beschrieben. (Tabelle 8).

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Résumé En 1960, des plants de pomme de terre certifiés importés d'Irlande ont montré une infection plus élevée que de coutume de gale argentée. Les tubercules atteints appartenaient aux cultivars Up-to-Date et Ulster Dale.Helminthosporium solani Dur. & Mont. fut identifié sur des échantillons de plants importés et d'origine locale. On a étudié la transmission de plants parentaux infectés aux tubercules-fils. Les tubercules infectés ont produit soit des touffes tout-à-fait indemnes d'attaque (Up-to-Date 25–91%, Ulster Dale 0–80%, Avenir 60%, Alpha 0%), soit des touffes partiellement ou complètement infectées (tableau 1). Rien n'indique que l'infection des tuberculesmères réduit la production des plantes. Les manifestations de l'infection sur les tubercules de divers calibres sont similaires (tableau 2). Faculté de conservation: il appara?t après stockage un ratatinement plus accentué chez les tubercules infectés. Ce phénomène est plus marqué en conservation froide (tableau 3), mais il n'appara?t aucun accroissement de gravité, ni aucune extension des taches de gale argentée. Dans des conditions normales de conservation, il se révèle une extension de la gale argentée sur les tubercules apparemment sains seulement lorsque ces tubercules proviennent de touffes partiellement infectées, et ainsi que sur les tubercules infectés conservés de janvier à avril. Les manifestations de la gale argentée sur les plants de pomme de terre certifiés importés figurent au tableau 4. Le tableau 5 montre la présence de la gale argentée dans la production locale issue de plants importés; la plupart des tubercules infectés proviennent de clones partiellement infectés, et très peu de clones montrent une infection totale. Chez Up-to-Date, les rubercules très infectés proviennent de plants importés (Hollande, Ecosse et Danemark). La présence de la gale argentée est très basse dans les plants locaux et diminue avec le nombre de reproductions en Isra?l (tableau 6); une différence appara?t entre les plants issus des trois périodes de croissance (tableau 7). Les manifestations de gale argentée dans divers cultivars sont mentionnées à le tableau 8.

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Formerly FAO Plant Quarantine Expert.     

Some properties of soils affecting russet scab and silver scurf of potatoes

The relationship of soil ammonia, nitrates, pH, total bacteria,Streptomyces sp., temperature and moisture on the incidence of russet scab and silver scurf of potatoes was studied. The soil properties were changed by the addition of various levels of alfalfa, wheat straw and green rye residues. Within the limits of the changes caused by these residues, the most consistent relationship was found between the nitrate level in the soil and russet scab, and to a lesser extent, silver scurf. In both instances there was a general decrease in russet scab and silver scurf with increasing levels of nitrates. Also, in the only comparison made, an increasing total bacterial count in the soil resulted in a decreasing level of infection from silver scurf. In some instances the alfalfa, rye and straw residue applications caused small changes in soil pH, soil temperature, and soil moisture. These changes were not great enough to show any consistent significant relationship to russet scab or silver scurf, except for a significant negative correlation between soil moisture at the 6-inch level and silver scurf in both years.     

Impact of a cultivar mixture on scab,powdery mildew and rosy aphid in an organic apple orchard

The impact of a cultivar mixture within the rows including the cvs Melrouge (low susceptibility to scab) and Pitchounette (Rvi6 resistant) was assessed during 2008–2009 in an organic apple orchard located in Rhône Valley (Drôme, France), on three important pests and diseases: scab, powdery mildew and rosy apple aphid. In this area, the resistance of Rvi6 gene was effective since the orchard plantation in 2004. The impact of the cultivar mixture was assessed per se, but also associated with sanitation practices to decrease the primary inoculum of scab and mildew, and compared to disease development on pure stands of Melrouge. The cultivar mixture showed a good efficiency to decrease the scab incidence on leaves and fruits; a significant effect on scab severity was observed in 2009 for the cultivar mixture plus sanitation practices. Our data confirmed the different susceptibility levels of the two cultivars for powdery mildew. Against powdery mildew, a favourable effect of cultivar mixture, at the condition it is associated with sanitation, was observed in case of a moderate level of the disease (2008). For rosy apple aphid, a favourable effect of cultivar mixture was observed on Melrouge in 2008 when Pitchounette has a good resistance level. In the context of organic production, the impact of the cultivar mixture seemed favourable for the control of the three pests and diseases.     

Resistance of potato to powdery scab (Spongospora subterranea) under andean field conditions

Six field trials were carried out in naturally infested soil to identify resistance to powdery scab. Trials were conducted at Anta, Cusco, in southern Peru (3300 m altitude) during six seasons. A scale of 1 (0%) to 9 (>95%) of tuber surface showing infection was used to evaluate resistance. Ratings 1–3 were considered resistant (R), 4 moderately resistant (R) and 5 or more, susceptible (S). Among 467 tested potato accessions (cultivars and advanced clones) of the potato germplasm collection held at the International Potato Center (CIP), 17 were R and 33 MR during two or more seasons. Another 55 were R and 70 MR during only one season. In addition, 251 were S and 41 did not grow for different reasons. Resistant were G-6, LT-6, DGV-103 A, Santiaguina, Alka Pinu, G84270.4, Serrana INTA, Esperanza, Gabriela, Albina, Primicia INTA, Pentland Crown, Ultimus, Katahdin, DTO-28, AL-624, and G81422.6. Cultivars Gabriela and Albina and clone G81422.6 can now be used by Cusco farmers because of their high yield, adaptability, and good resistance to powdery scab.     

Reliability of methods of assessing the degree of tuber attack by common scab of potatoes

Summary Four methods of assessing the degree of tuber attack by common scab caused byStreptomyces scabies (Thaxt.) Waksman and Henrici were compared in five experiments, over three years at two locations. The experiments were conducted on light, naturally infested soils in counties Wexford and Carlow. Comparison of the coefficients of variation showed that the cover score method gave the least consistent results. The other three methods gave consistent results. Of these the visual assessment (0–10) of tubers in the field and the highest scab method were the easiest and quickest methods to operate.     

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.