Potato leafroll virus and potato virus Y in seed potatoes used to plant the North Carolina crop

Incidence of potato leafroll virus (PLRV) and potato virus Y (PVY) was determined in seed potatoes (Solatium tuberosum) from Canada, Maine, Minnesota, New York, North Dakota, Nebraska, Pennsylvania, and Wisconsin used to plant the North Carolina crop in 1977, 1978 and 1979. Incidence of PLRV ranged from 0–5.2% (X = 0.57%) and for PVY from 0-5.6% (X = 0.62%) from all sources (112 seed lots). All PVY isolates (177) tested from potato caused a very mild veinbanding and mottling onNicotiana tabacum cultivars NC 95 and NC 2326. No serological difference was detected between these isolates and the common strain of PVY from tobacco in North Carolina. Essentially no spread of PVY occurred in three potato fields observed each year of the study.     

Comparison of Mineral Oil and Rapeseed Oil Used for the Protection of Seed Potatoes against PVY and PVM Infections

The aim of this research was to compare the effectiveness of mineral oil with rapeseed oil in the protection of potato seeds against Potato virus Y (PVY) and Potato virus M (PVM) infection. The research was carried out under field conditions in the north of Poland, in the Department of Potato Protection and Seed Science of the Plant Breeding and Acclimatization Institute??National Research Institute at Bonin. The effects of oil protection on potato seed infection by viruses, yield, and its structure and phytotoxity were assessed. Two rapeseed oils and one mineral oil were used: Olejan 85 EC (85% of natural rapeseed oil), alimentary oil Marlibo (100% of natural rapeseed oil) and Sunspray 850 EC (98.8% mineral oil+1.2% emulsifier). The effectiveness of oils in protection against PVY and PVM tuber infection was tested on two cultivars (Clarissa and Rosalind), which have a different level of resistance to the two viruses. The assessment of phytotoxicity was carried out on 10 potato cultivars from different earliness groups (Augusta, Bryza, Cekin, Clarissa, Impala, Krasa, Rosalind, Satina, Velox). Two oil concentrations, 2% and 4% were applied. During the growing period, eight to nine oil treatments were applied at 7-day intervals. The effectiveness of rapeseed oils against PVY and PVM was much weaker than that of the mineral oil and for the susceptible cultivar the percentage infected tubers did not differ significantly from untreated crops. However, Olejan 85 EC deserves attention as it significantly reduced PVY infection across years in the more resistant cultivar, especially in the case of a lower concentration (2% vs. 4%). When there are no other means of protection to use on organic seed plantations, this oil can be used as an alternative, especially in the case of cultivars which are moderately resistant to PVY. A disadvantage of its application may be the fact that in some years symptoms of phytotoxicity on potato plants were recorded and a lowering of tuber yield.     

Potato Breeding and Seed Production System Development in Russia

First, an extensive literature review was performed with respect to Potato virus Y (PVY) resistance sources and their further utilization in a breeding programme. On the basis of that review we present a scheme of backcrossing and new cultivar creation on the basis of five detected sources of PVY resistance and one source of Potato virus X resistance. Some cultivar pedigrees are presented reflecting the differences in the breeding strategies. Moreover, results of investigations on some polygenic traits such as field resistance against late blight and starch content are presented. For these purposes progenies were screened for suitable recombinant genotypes which were used in further crossings. Also the results of investigations on resistance to the potato golden nematode and on the selection of cultivars suitable for processing are briefly analysed. We also describe a programme of parallel evaluation of identical hybrid populations in different soils and climatic zones. The development of seed potato production systems facilitated the conditions to improve the quality of potato seed material, to increase potato production and to allow Russia to participate in the international potato market. Systems of virus detection, norms and methods of laboratory tests as well as requirements for quality and tolerance levels of different seed classes (generations) were unified and harmonized with European systems.     

The Rate of Virus Spread in New Potato Cultivars in the North of Poland

The aim of this research was to assess the rate of increase in the level of tuber infection by PVY, PVM, and PLRV during three consecutive years of multiplication in the field for 17 new cultivars registered in Poland in 2009–2011 and for two cultivars not listed in the registry but popularly cultivated. The research was conducted in Bonin near Koszalin (north-western Poland) in 2010–2013. Tuber infection was assessed using DAS ELISA in a grow-out test in the winter-spring period. Among the 19 cultivars examined, eight had high resistance to PVY (above grade 8 on a scale of 1–9); during the 3-year research period, they were not infected. Also, cv. Gawin seemed more resistant than previously assumed. In contrast, cvs. Hermes and Sylvana, which were rated in the Netherlands as quite resistant, were clearly very susceptible (grade 3–4) in Polish conditions, as within 2 years 100% of tubers were infected with this virus. The greatest susceptibility to PVM was shown by cvs. Danuta and Stasia, 50% of which were infected, despite moderate exposure to the virus. Cultivars Zenia, Etiuda, Jubilat, and Viviana appeared very resistant to PVM as the number of infected tubers did not exceed 5%. PVM was not detected in the tubers of cvs. Bursztyn, Gustaw, and Legenda, which confirmed that these cultivars possess the Rm gene. Not all cultivars regarded susceptible (grade 3–4) to PLRV were infected. The virus was not found in tubers of cv. Bursztyn, while in cv. Hermes, assessed in the Netherlands as being quite resistant, almost 40% of tubers were infected.     

Potato Plants Grown from Minitubers are Delayed in Maturity and Lower in Yield,but are not at a Higher Risk of <Emphasis Type="Italic">Potato virus Y</Emphasis> Infection than Plants Grown from Conventional Seed

Potato virus Y (PVY) is the most important virus in North American seed potato (Solanum tuberosum L.) production. Planting virus-free minitubers in place of field-grown seed, which usually has a low PVY incidence, reduces initial PVY inoculum in the field. However, plants grown from minitubers are smaller and emerge later than those grown from conventional seed, which could make them more likely to become infected with PVY. We tested the effects of seed type of three potato cultivars (Dark Red Norland, Goldrush, and Red La Soda) on PVY incidence, tuber yield, and flowering time. The incidence of PVY in plants grown from minitubers did not differ from that of plants grown from conventional seed. Minituber-grown plants produced lower tuber yields than plants grown from conventional seed. Plants from minitubers also emerged and flowered later, but this did not increase their incidence of PVY. Cultivar-specific differences were observed in tuber yield and flowering times, suggesting that this variation may influence PVY incidence more than seed type.     

Occurrence and Distribution of Potato Pests and Diseases in Kenya

Potato plays an important role in food security in Kenya but yields are low (<10 t/ha), and this is partly attributed to the lack of healthy planting material. This study is the first wide-scale survey to determine the occurrence and distribution of common potato pests and diseases in Kenyan seed (certified and quality declared) and ware crops. Potato crops growing on 101 farms in 21 districts were examined. Approximately 36% of plants in farmers’ fields sampled both during the long rains (main potato-growing season) and short rains seasons displayed virus-like disease symptoms. Six viruses (potato leafroll virus (PLRV), Potato virus A (PVA), potato virus M (PVM), potato virus S (PVS), potato virus X (PVX), and potato virus Y (PVY)) were detected using double antibody sandwich enzyme-linked immunosorbent assay in potato samples. Sequencing of polymerase chain reaction products from PVY-infected plants revealed the presence of recombinant strains of PVY (NTN and Wilga). Four aphid species, Macrosiphum euphorbiae, Aphis gossypii, Myzus persicae, and Aphis fabae, colonized potato in all districts, occurring in greater numbers west of the Great Rift Valley than to the east. There was a positive correlation between virus incidence and aphid numbers in the long rains (main) potato-growing season. PLRV, PVM, PVS, PVX, and PVY were detected in solanaceous weeds. Ralstonia solanacearum was detected in soils from 13 farms in 8 of the 18 districts surveyed. Approximately 38% of soil samples were infested with Meloidogyne spp. Phytophthora infestans isolates belonging to the US 1 and 2_A1 genotypes were identified. Although many economically important diseases are present in Kenya, the lower aphid incidence in districts east of the Great Rift Valley may indicate that these districts are more suitable for seed potato production.     

Factors influencing PVY development and disease expression in three potato cultivars

Studies were performed to investigate factors affecting symptom expression of potato virus Y infection in three potato cultivars, Russet Norkotah, Shepody, and Red LaSoda. Quantitative enzyme-linked immunosorbent assay (ELISA) results revealed few differences in the relative virus titer among cultivars tested. Potato virus Y (PVY) titers developed as rapidly in Russet Norkotah as in Shepody and Red LaSoda. Additional studies were performed to determine the effect of light intensity and infections of PVY and potato virus X (PVX), alone and in combination, on the expression of mosaic symptoms in these three cultivars. Low light intensity (270-330 uE/m²/sec) significantly increased plant heights and severity of mosaic disease among the cultivars compared to high light intensity (100-200 uE/m²/sec). PVX and PVY, as well as the combination of PVX and PVY in the same plant, decreased plant height compared to the uninoculated (healthy) controls. Low light intensity and dual infections of PVX and PVY significantly increased mosaic disease severity in Shepody and Red LaSoda, but not in Russet Norkotah. Results of these studies refute the suggestion that Russet Norkotah is resistant to PVY infection since virus titers in this cultivar are similar to the known susceptible cultivars Shepody and Red LaSoda. These results further suggest that while Russet Norkotah is fully susceptible to infection by PVY, it resists symptom expression.     

Potato Cultivar and Seed Type Affect the Development of Systemic <Emphasis Type="Italic">Potato virus Y</Emphasis> (PVY<Superscript>N-Wi</Superscript>) Infection

Potato virus Y (PVY) infection is one of the greatest challenges to seed potato production in the United States. To determine how cultivar and seed type affect the development of systemic PVY infection, Russet Burbank and Russet Norkotah Colorado 3 cultivars were grown from two types of pre-nuclear seed (i.e., plantlets and minitubers) and Generation 3 (G3) tubers and challenged with PVY strain Wilga (PVY^N-Wi). Systemic PVY infection was measured by assaying spread of virus from the inoculation site to upper non-inoculated leaves. The Burbank cultivar had a lower incidence of systemic PVY infection compared to the incidence of systemic PVY that developed in the Colorado 3 cultivar. Furthermore, Burbank plants grown from G3 tubers had a lower incidence of systemic PVY infection, as compared to Burbank plants grown from plantlets. Together our results indicate that both cultivar and seed type affect the development of systemic PVY^N-Wi infections post-inoculation.     

New isolates of the necrotic strain of potato virus Y (PVYN) found recently in Poland

Summary In comparison to the previously known isolates of potato virus Y^N (PVY^N), some isolates found in Poland since 1984 are more infectious to potato plants, reach faster a higher concentration and induce milder disease symptoms. Potato cultivars resistant to the standard type of PVY_N may be susceptible to the new isolates whereas those that are extremely resistant to PVY remain extremely resistant to the new isolates. The potato cultivar Elipsa is suitable for the differentiation of PVY^N isolates.     

The effect of metribuzin interaction with potato viruses X and Y on potato foliage,yield and grade

Foliar treatment of potato (Solanum tuberosum L.) with metribuzin at 0.57–1.0 lb/A caused a necrotic reaction in leaflets of plants infected with potato virus Y (PVY), but not in plants infected with potato virus X (PVX) or potato leafroll virus. Necrosis symptoms resulting from metribuzin-PVY interaction were distinct from symptoms of either PVY infection or of metribuzin injury. This reaction was similar in the Russet Burbank, Lemhi Russet, and Pioneer cultivars. Russet Burbank infected with PVY and PVX, alone or in combination, was treated with metribuzin to study herbicidevirus interaction effects on yield. Secondary PVY infection alone caused a 57% yield reduction, and when combined with PVX caused a 71% yield reduction. Although leaflet necrosis was induced by the metribuzin-PVY combination, there was no significant yield interaction. Results suggest that post-emergence application of metribuzin can be used as an aid for detecting and removing potato virus Y infected plants from potato seed fields     

Occurrence of Viruses Affecting Potato Crops in Khartoum State-Sudan

The incidence of Alfalfa mosaic virus (AMV), Potato leafroll virus (PLRV), and Potato virus Y (PVY) in potato crops derived from various types of seed potatoes was assessed visually and confirmed by direct tissue blot immunoassay, over two winter growing seasons (1999/2000, 2000/2001) at three locations, Elnaiya, Elshehinab, and Shambat in Khartoum State, the main potato growing region in Sudan. Virus infection was most prevalent in 2000/2001. In general, crops grown directly from imported certified seed potatoes and from “improved seed”, produced in Sudan from imported basic seed, showed the lowest levels of PLRV and PVY compared with crops grown from Sudanese farm saved seed. For AMV, however, only crops grown directly from imported certified seed potatoes had low levels of AMV. Crop location also affected virus incidence, although this varied with year. For AMV, levels were similar at all locations in 1999/2000, but were greatest at Elnaiya in 2000/2001. For PVY, levels were greatest at Elnaiya in 1999/2000 and Shambat in 2000/2001. For PLRV, no symptoms were observed in 1999/2000 and virus levels were similar for all locations in 2000/2001. This study reports for the first time the occurrence of AMV in potatoes grown in Sudan.     

Evidence of potato virus Y asymptomatic clones in diploid and tetraploid potato-breeding populations

Potato virus Y (PVY) is a potyvirus affecting potato productivity by reducing yield and quality. To reduce the amount of PVY in potato production systems, state seed certification agencies have established threshold criteria, which simultaneously increase quality. Research has documented several commercial cultivars lacking symptom expression of PVY despite infection. The presence of PVY asymptomatic clones in production and breeding populations is particularly important because it may provide an inoculum source in breeders’ seed and this reduces the efficiency of selection. The objectives of this research were to determine to what extent PVY asymptomatic clones are present in potato-breeding populations, and if PVY expression is influenced by the environment. After exposure to PVY, genotypes from different 2x and 4x populations were evaluated for the presence of PVY both visually and by ELISA assay. PVY asymptomatic genotypes were identified in both 2x and 4x populations. Chi square indicated dependency between PVY symptom expression and (1) ploidy, (2) genetically distinct 4x germplasm enhancement populations, and (3) expression in a north temperatevs. tropical environment using 4x progeny from five half-sib families. Dependency was not found between two 4x genetically related sub-populations and PVY asymptomatic expression. Analysis of variance (ANOVA) indicated that clones within family, families, location, and the interaction of location by clone were significant sources of variation for PVY symptom expression, ELISA, and visual evaluation. PVY asymptomatic clones were present in both 2x and 4x populations with higher frequencies in a north temperate compared to a tropical environment, suggesting that PVY symptom expression may be influenced by the environment.     

Identification of triplex (YYYy) Potato Virus Y (PVY) immune progenitors derived fromSolanum tuberosum ssp.andigena

As part of the International Potato Center’s (CIP) virus resistance breeding strategy, a group of 182 selected clones from intercrosses among duplex Potato Virus Y (PVY) immune progenitors derived fromSolanum tuberosum ssp.andigena (i.e., YYyy × YYyy) was sampled. These clones were test-crossed to the PVY susceptible tester 377964.5 (yyyy) to search for triplex (YYYy) and quadruplex (YYYY) PVY immune potato progenitors. Seedlings of each test-crossed progeny were screened for PVY immunity. Genetic analysis of observed ratios for immunity-susceptibility showed that two of the 182 clones segregated as triplex under the assumption of a random chromatid segregation model. The double reduction coefficient, α, and its standard error were estimated from the experimental data, and had values of 0.1566 and 0.0186 respectively. These results indicated that crossovers take place during meiosis between the locus and the centromere, permitting sister chromatids to migrate to the same pole producing a random chromatid segregation. In the population evaluated, no clone was identified as a quadruplex. The two triplex PVY immune genotypes will produce about 96% of progenies with PVY immunity when mated to PVY susceptible advanced clones or varieties. These progenitors have the potential to provide a durable PVY genetic control and diminish the present impact of this virus on the potato crop. Also, immunity to PVY will significantly simplify the seed production process.     

Genetic Resistances to Potato Leafroll Virus, Potato Virus Y, and Green Peach Aphid in Progeny ofSolanum etuberosum

Increasing prevalence of potato leafroll virus (PLRV) and potato virus Y (PVY) has been reported in seed and commercial potato production, resulting in the rejection of potatoes for certification and processing. Host plant resistance to PLRV and PVY and their primary vector, green peach aphid,Myzus persicae, could limit the spread of these viruses. Host plant resistance to PLRV, PVY, and green peach aphid has been identified in non-tuber-bearingSolanum etuberosum (PI 245939) and in its backcross 2 (BC₂) progeny. Resistance to green peach aphid involved a reduction in fecundity and adult aphid size. In addition, one BC₂ individual was identified as possessing a genetic factor that was detrimental to nymph survival. PVY resistance was identified in all five BC₂ progenies evaluated in a field screening under intense virus pressure. PLRV resistance was identified in two of the five BC₂ progeny. This resistance was stable in field and cage evaluations with large populations of viruliferous aphids. Based on the segregation of virus resistances in the BC₂ , PVY and PLRV resistances appear to result from the action of independent genetic mechanisms that reduce the levels of primary and secondary virus infection. Two BC₂ individuals, Etb 6-21-3 and Etb 6-21-5 were identified as having multiple resistances to PLRV, PVY, and green peach aphid derived fromS. etuberosum. This germplasm could prove useful to potato breeders in the development of virus-resistant cultivars.     

Assessment of Possibilities of Microtuber and in vitro Plantlet Seed Multiplication in Field Conditions. Part 1: PVY,PVM and PLRV Spreading

Currently in vitro plantlets and microtubers provide the basis for pre-base production of potato seeds, from which minitubers are produced under covers – they serve later as seed material to be planted in the field. The aim of the research was to determine the possibility for multiplication of material produced in vitro directly in field conditions. The research assessed PVY, PVM and PLRV infection of potato tubers derived from plants grown directly from in vitro plantlets, microtubers, minitubers and traditional seed potatoes planted in the field at different times. Moreover, testing in laboratory conditions, the susceptibility of these plants to virus infection was determined for the case of artificial inoculation of Myzus persicae and Aphis nasturtii. It was found that the infection of tubers derived from in vitro plantlets and microtubers was greater than that of seed potatoes and minitubers. Yet it seems that the reason for their higher infection level resulted not from the plant’s sensitivity or its greater attractiveness to aphids but from a largely unknown cause. Earlier planting of microtubers and in vitro plantlets in the field in case of the more resistant cultivar and certainly later in relation to the main time of planting had an impact on limiting the PVY and PVM infection of potato tubers. Hence multiplication of microtubers and in vitro plantlets in field conditions could be very economical using cultivars which are relatively resistant to viruses. However, adopting a later than usual planting period (end of June) and applying an additional protective cover (such as non-woven agricultural fabric) in the first period of a plant’s growth, promotes multiplication of microtubers and in vitro plantlets in field conditions for cultivars with low resistance levels.     

Comparative levels of potato viruses S and Y infection of microplants and tuber-propagated plants in the field

The practice of transplanting microplants from tissue-culture to the field was compared to normal tuber propagation with respect to the transmission and translocation of potato virus S (PVS) and potato virus Y (PVY) to the daughter tubers of Red Pontiac, Shepody, Kennebec, and Russet Burbank cultivars in Prince Edward Island in 1984 and 1985. In general, the use of microplants to produce seed stocks appeared to increase the risk of infection with both viruses, although the results for tuber infection with PVY were only significant in one of the years.     

New disease symptoms observed on field-grown potato plants with potato spindle tuber viroid and potato virus Y infections

Summary Potato spindle tuber viroid (PSTV) and potato virus Y (PVY) were isolated from plants of cultivar Kennebec with severe necrotic symptoms in the field. In the greenhouse, severe necrotic symptoms were reproduced only when potato plants were infected either simultaneously with PSTV+PVY, or with PSTV prior to PVY infection. Thirteen additional potato cultivars were tested in the greenhouse for this synergistic reaction and eight developed necrotic responses similar to cv. Kennebec. PVY concentration was significantly higher in doubly infected plants, compared with those infected with PVY alone.     

Use of the virus strain group concept to characterize the resistance to PVX and PVYo in the potato cv Allegany

Resistance to the potato viruses X (PVX), Y (PVY) and A (PVA) was examined in the potato cv Allegany released by Cornell University in 1990. Standard potato cultivars from North America and Europe were included for characterization of the resistance response. Allegany was extremely resistant to a strain group 3 isolate of PVX and reacted with hypersensitivity to an ordinary strain isolate of PVY (PVY^o). However, Allegany was susceptible to an isolate of PVY causing necrosis in tobacco (PVY^N), and to an isolate of PVA. No symptoms appeared following infection with PVY^N and PVA. Identification of existing virus strain groups in a geographic area is an important aspect of predicting cultivar response to inoculation in the field.