Spraing

Abstract: Contents Potato Disease, Pest and Disorder Diagnostics 1 Bacterial Diseases 2 Fungal and Fungal-like Diseases 3 Viral and Phytoplasma Diseases 4 Nematodes 5 Insects and other Pests 6 Non-infectious Disorders: chemical, nutritional & physical environmental physiological Glossary Index Diseases and Pests covered: * Potato early blight * Gray mould * Black dot * Ring rot * Blackleg * Soft rot * Pit rot * Dry rot and wilt * Violet root rot * Silver scurf * Aster yellows * Witches broom * Pocket rot * Gangrene * Pink rot * Potato late blight * Skin spot * Spraing * Mild Mosaic * Sev. Mosaic * Net Necrosis * Watery wound rot * Leak, Brown rot * Stem canker * Black Scurf * White mould * Powdery scab * Common scab * Wart * Spraing * Verticillium wilt

Abstract: SUMMARY At a site in eastern Scotland, nine common species of arable weeds were infected with tobacco rattle virus (TRV), and some of these, notably Viola arvensis and Stellaria media, comprised an overwintering reservoir of the virus. TRV was seed-borne both in naturally and in experimentally infected V. arvensis (2–10%), and occasionally in other weed species. In the glasshouse at 20 oC a naturally infective population of vector nematodes (Tricho-dorus spp.) kept in soil free of plants retained its infectivity for 20 wk, although few Trichodorus survived for this period. In the field, the incidence of TRV infection in potato (spraing disease) in plots kept free of weeds for 1–5 years was 3–4 times that in weed-infested plots but Trichodorus numbers did not differ appreciably between the two treatments. Presumably the virus is retained for long periods in its vectors and these feed on potato more frequently when other hosts are not available. Weeds are probably important in the long term as hosts of both TRV and its vectors, but in the short term weed control seems unlikely to prevent potato spraing because of the long persistence of TRV in vector populations. In the field, Trichodorus accumulated near the interface between topsoil and subsoil, and the incidence of spraing was greatest where the topsoil was shallowest. When cucumber seedlings were exposed to virus-carrying Trichodorus, TRV reached a greater concentration in roots at 20 oC than at 24 oC, and the virus was not detected in roots at 29 oC. In a sandy soil, TRV was transmitted only when the water content exceeded 15%, and at least 30 % water was needed for maximum transmission. Annual records of rainfall and spraing disease suggest that spraing is most prevalent when the summer is wettest. TRV is not confined to cultivated land. Stabilized sand dunes supporting a pure stand of Ammophila armaria were colonized by Trichodorus pachyder-mus, but TRV was detected only where the plant community had enlarged to include V. arvensis and other dicotyledons. In such situations, TRV may be introduced in the seed of V. arvensis, and the movement of soil by wind probably contributes to the dispersal of Trichodorus.

Abstract: Potato mop-top virus (PMTV, genus Pomovirus) causes severe quality problems by inducing necrotic arcs (spraing symptoms) in potato tubers. In this study, coat protein (CP) gene and read-through domain of RNA2 and 8K gene and 3′ untranslated region of RNA3 were characterized from 37 PMTV isolates detected in tubers from fields in Finland and a screenhouse in Latvia. Two distinguishable types of RNA2 and RNA3 were found, each showing only little genetic variability. Sequencing and restriction fragment length polymorphism analysis of polymerase chain reaction amplicons indicated that the majority of PMTV isolates infecting tubers comprise restrictotypes RNA2-II and RNA3-B. The incidence of PMTV-infected tubers in 2006 (2007) was 55 (60), 33 (39), and 62 (68)% in cvs. Kardal, Saturna, and Nicola, respectively, grown in the same field in 2006 (2007). Incidence of PMTV-infected tubers that were symptomless was 100 (90)% in Kardal and 88 (44)% in Saturna, and also high in cvs. Bintje (95%) and Van Gogh ...

Abstract: The occorrence of potato mop-top virus (PMTV) was assessed by two different soil sampling methods. PMTV was prevalent in southwestern Sweden but was not detected in the northern part of the country. In storage trials more symptoms developed in tubers kept at 9°C than 4 °C. irrespective of the cultivar. Cutting the tubers enhanced post storage symptom develoment in some cultivars. Of 14 cultivars grown in Sweden, those used for crisp products were more inclined to develop spraing than the others. A comparison of the severity of PMTV symptoms in field trials in Sweden. Denmark and Finland indicated substantial geographic variation in the relative susceptibility of different cultivars suggesting variation among isolates of the virus. From glasshouse experiments it was found that inoculations done at flower bud development or at flowering resulted in most spraing. Cultivar trials in pots produced a low level of spraing symptoms in general.