Breakdown of potato virus X resistance gene NX: selection of a group four strain from strain group three

Isolate DX of potato virus X (PVX) caused the typical reactions of a group three strain, systemic top necrosis in presence of potato hypersensitivity gene Nx and mosaic with gene Nb. When tubers harvested from DX-infected plants of the Nx: Nb cultivars Maris Piper and Pentland Dell were, grown on, most progeny plants were healthy, but some had systemic top necrosis caused by DX while others had mosaic symptoms in upper leaves and severe necrosis in lower ones. Infective sap from the plants with mosaic and necrosis always caused similar symptoms when inoculated to Pentland Dell. Only group four PVX strains can cause systemic infection without top necrosis in Nx:Nb cultivars, so the affected plants all contained a group four strain. That the severe necrosis of their lower leaves resulted from a shock reaction rather than from isolate DX also being present was indicated because the plants partially recovered, inoculations from near to the dilution end-point failed to demonstrate any separation of strains and behaviour on back-testing to Pentland Dell was unchanged after passage twice through tubers of this cultivar. Also, although DX caused severe necrotic symptoms in tubers of both Nx: Nb cultivars, these symptoms did not develop in tubers of plants with mosaic and necrosis. When cultured serially in Nicotiana glutinosa , the group four strain eventually reverted to group three.     

Factors affecting the development and control of black dot on potato tubers

Field trials were carried out over a 4 year period (2004–2007) to determine the effect of agronomic factors, specifically cultivar resistance, irrigation, crop duration and chemical control (in‐furrow application of azoxystrobin), on black dot development on potato tubers grown in fields where soilborne inoculum of Colletotrichum coccodes was present. In 2004, 2005 and 2006, two field trials were performed each year and in 2007, 19 mini‐field trials were carried out across Scotland and England. Cultivar resistance was clearly demonstrated to be an effective method of reducing black dot disease severity on tubers (described here as the percentage of unmarketable tubers, i.e. those with symptoms covering a surface area of >10%). In the four field trials carried out in 2004 and 2005, in irrigated and fungicide‐untreated plots, 43·8% of tubers of cv. Maris Piper were unmarketable, compared with 17·0% of tubers of cv. Sante. Assessments of disease development on underground plant parts (stems, stolons and roots) revealed that cultivar resistance acted only at the tuber level, as disease symptoms on other parts were often high irrespective of published disease resistance ratings. Irrigation increased the severity of disease on tubers in two trials (England 2004 and 2006), but its effect was less significant when rainfall was high. Delaying harvest by 2 weeks increased disease severity in all six trials, whilst application of azoxystrobin consistently reduced black dot severity. There were significant interactions between factors. The results clearly show how black dot disease severity can be reduced through an integrated approach to disease management.     

一个马铃薯X病毒分离物的外壳蛋白基因序列分析与株系鉴定

对山东省侵染马铃薯的一个马铃薯X病毒(PVX)分离物PVX—SD1的外壳蛋白(CP)基因进行了克隆和序列分析。以提纯的病毒RNA为模板，应用RT-PCR扩增目的基因，通过常规的基因克隆法将扩增的CP基因导入pUC19载体，测序。结果表明，PVX—SD1的CP基因长719bp，可编码248个氨基酸；与Gen—Bank中报道的15个有代表性的株系或分离物相比较，核苷酸同源性在80．1％-99．7％，氨基酸同源性在89．8％-100％；与欧洲株系UK3仅1个核苷酸不同，同源性为99．7％，氨基酸同源性达100％，表明它们可能为同一株系，属于X^3组．     

Effect of plant genotype, virus isolate and temperature on the expression of the potato tuber necrotic ringspot disease (PTNRD)

The present study shows that a large range of potato cultivars (29/33 tested), widely grown in the world, are susceptible to potato tuber necrotic ringspot disease caused by potato virus Y. The three factors studied in this work, which proved to influence the level of tuber necrosis reaction, were, first, the plant genotype, since varietal behaviour exhibited large differences; second, the virus genotype, since variations of virulence occurred between the four isolates tested; and third, the environmental conditions, as shown by the different rates of tuber necrosis obtained under contrasting conditions of temperature as much during the growing period as during storage. Three of the cultivars tested, Spunta, Maris Piper and Thalassa, failed to produce necrotic tubers, although infected with a virulent tuber-necrosing isolate. This result, following observations on the inheritance of the tuber necrosis trait, suggests that at least a major dominant gene controls this reaction in non-sensitive cultivars. On the other hand, the extreme resistance genes ( Ry ) provide a good resistance to virus infection, thus, preventing tuber necrosis under field conditions.     

Molecular breeding for virus resistant potato plants

To engineer resistance against potato virus X (PVX), the viral coat protein (CP) gene has been introduced into two potato cultivars. Stable expression of the gene in transgenic clones throughout the growing season has been obtained and resulted in considerably increased virus resistance. With varying frequencies depending on the original cultivar used, true-to-type PVX resistant transgenic clones have been obtained. Since deviant light sprout characteristics were invariably associated with aberrations in plant phenotype, they can be used in procedures to early screen for deviations. Furthermore, it has been possible to unequivocally discriminate between the original untransformed and independent transgenic cultivars. Although no relation has been found between the presence, if any, of the CP of potato virus Y (PVY) or potato leafroll virus (PLRV) in CP gene transgenic potato, appreciable levels of resistance to these viruses has been obtained. This suggests that the mechanism by which a viral CP gene in the potato genome evokes resistance, differs amongst various viruses.     

Molecular breeding for virus resistant potato plants

To engineer resistance against potato virus X (PVX), the viral coat protein (CP) gene has been introduced into two potato cultivars. Stable expression of the gene in transgenic clones throughout the growing season has been obtained and resulted in considerably increased virus resistance. With varying frequencies depending on the original cultivar used, true-to-type PVX resistant transgenic clones have been obtained. Since deviant light sprout characteristics were invariably associated with aberrations in plant phenotype, they can be used in procedures to early screen for deviations. Furthermore, it has been possible to unequivocally discriminate between the original untransformed and independent transgenic cultivars. Although no relation has been found between the presence, if any, of the CP of potato virus Y (PVY) or potato leafroll virus (PLRV) in CP gene transgenic potato, appreciable levels of resistance to these viruses has been obtained. This suggests that the mechanism by which a viral CP gene in the potato genome evokes resistance, differs amongst various viruses.     

Interactions between Globodera pallida juveniles, Verticillium dahliae and three potato cultivars, with descriptions of associated histopathologies

Experiments carried out in agar culture showed that the potato cultivar Pentland Javelin is relatively resistant to infection by Verticillium dahliae because it has a multilayered cortex of thick-walled cells, each producing lignituber appositions to invading hyphae. Its thick-walled xylem vessels are difficult to penetrate, its large vessel lumens difficult to obstruct, and its ability to produce tyloses limits the spread of the fungus, By comparison. Maris Anchor roots have fewer cortical layers and very small xylem vessels which are more easily blocked by hyphae. Maris Peer is intermediate in both the number of cortical cell layers and the size of xylem vessels. Globodera pallida juveniles assist V. dahliae to evade the natural defences of the root by opening an invasion channel for the fungus. In Maris Anchor and Maris Peer, but not in Pentland Javelin, the nematode provokes a widespread hypersensitive response; the resulting cell wall lignification impedes the growth of those hyphae which invade several days after the nematode. Hyphae grow well in syncytia and this enhances the probability of their penetrating xylem vessels. Although V. dahliae is generally held to induce symptoms through xylem blockage, the phloem colonization which was noted may affect the growth of both plant and nematode through its effect on assimilate movement towards root lips and into syncytia.     

Mature plant resistance of potato against some virus diseases. I. Concurrence of development of mature plant resistance against potato virus X,and decrease of ribosome and RNA content

Four of five weeks after planting a group of potato plants ‘Bintje’ was inoculated with potato virus X (PVX). Other groups were inoculated at intervals of 14 days. Tubers produced by plants inoculated 35 days after planting were all infected. The plants inoculated 49 days or later after planting produced few infected tubers. The latter had developed mature plant resistance against PVX infection. The ribosome and RNA contents of leaves were measured by application of adsorption chromatography. A rapid decrease in ribosome and RNA contents occurred in plants at the time of rapid increase in the rate of mature plant resistance. The decrease was most distinct in the fifteenth leaf and therefore the contents in this leaf seem to give a good indication of the rapid increase in resistance.     

马铃薯Y病毒N-Wi株系广西分离物的鉴定

 马铃薯Y病毒 (potato virus Y,PVY) 是一种重要的农作物病毒,可造成产量损失和产品质量下降。其宿主范围广泛,包括马铃薯、烟草、番茄和辣椒等经济作物。在广西从叶片表现斑驳褪绿症状的马铃薯上分离到一株PVY分离物DX,其基因组包含一个大的开放阅读框 (open reading frame,ORF),由9 186 nt组成,编码3 061个氨基酸。系统发育进化分析显示,分离物DX与PVY^N-Wi株系分离物IUNG-12、SGS-AG、MAF-VOY聚类成一个分支。重组分析表明分离物DX基因组在496 nt和2 388 nt存在重组位点,分别位于P1和HC-Pro/P3结合区,是分离物Oz和N605的重组体。通过机械摩擦接种,分离物DX可侵染茄科9种作物,引起本生烟叶片花叶、皱缩和泡状突起等症状;引起普通烟草和番茄的轻微花叶症状;引起马铃薯叶片花叶症状,接种辣椒没有发病。序列比对分析显示,分离物DX缺乏引起烟草叶脉坏死相关的氨基酸位点N₂₀₅、K₄₀₀和E₄₁₉。本研究比较了分离物DX对茄科共12种作物的侵染能力和病害症状差异,结果表明分离物DX可用于探索PVY在不同寄主中的致病机理。     

Transgenic potato plants expressing the potato virus X (PVX) coat protein gene developed resistance to the viral infection

The gene coding for potato virus X (PVX) coat protein (CP) was expressed in transgenic potato plants obtained byAgrobacterium tumefaciens transformation. One hundred independent clones were analyzed in challenge experiments for resistance to PVX infection under greenhouse conditions as a preliminary test. From this test, 16 clones with the best resistance results were selected for a small-scale field trial. Clones 54, 60, 73 and 91 demonstrated the best values of resistance to PVX in the field. Statistical analysis of the field trial showed significant differences between means of optical density obtained in ELISA from transgenic clones and non-transformed plants (P<0.05). There was correspondence between resistance to virus infection and expression of the CP gene of PVX virus in the analyzed clones. http://www.phytoparasitica.org posting Jan. 21, 2002. Corresponding author [e-mail: vivian.doreste@cigb.edu.cu].     

Identification of the molecular make-up of the Potato virus Y strain PVY(Z): genetic typing of PVY(Z)-NTN

Potato virus Y (PVY) strains were originally defined by interactions with different resistance genes in standard potato cultivars. Five distinct strain groups are defined that cause local or systemic hypersensitive responses (HRs) in genetic background with a corresponding N gene: PVY(O), PVY(N), PVY(C), PVY(Z), and PVY(E). The nucleotide sequences of multiple isolates of PVY(O) and PVY(N) differ from each other by ≈8% along their genomes. Additionally, complete genome sequences of multiple recombinant isolates are composed of segments of parental PVY(O) and PVY(N) sequences. Here, we report that recombinant isolate PVY-L26 induces an HR in potato 'Maris Bard' carrying the putative Nz gene, and is not recognized by two other resistance genes, Nc and Ny(tbr). These genetic responses in potato, combined with the inability of PVY-L26 to induce vein necrosis in tobacco, clearly define it as an isolate from the PVY(Z) strain group and provide the first information on genome structure and sequence of PVY(Z). The genome of PVY-L26 displays typical features of European NTN-type isolates with three recombinant junctions (PVY(EU-NTN)), and the PVY-L26 is named PVY(Z)-NTN. Three typical PVY(NTN) isolates and two PVY(N) isolates, all inducing vein necrosis in tobacco, were compared with PVY-L26. One PVY(NTN) isolate elicited HR reactions in Maris Bard, similar to PVY-L26, while two induced a severe systemic HR-like reaction quite different from the quasi-symptomless reaction induced by two PVY(N) isolates. 'Yukon Gold' potato from North America produced HR against several PVY(NTN) isolates, including PVY-L26, but only late and limited systemic necrosis against one PVY(N) isolate. Consequently, according to symptoms in potato indicators, both PVY(Z) and PVY(NTN) isolates appeared biologically very close and clearly distinct from PVY(O) and PVY(N) strain groups.     

A coat protein transgene from a Scottish isolate of potato mop-top virus mediates strong resistance against Scandinavian isolates which have similar coat protein genes

Resistance tests were made on seedlings of transformed lines of Nicotiana benthamiana which contain a transgene encoding the coat protein (CP) gene of a Scottish isolate of potato mop-top virus (PMTV). This transgene has been reported to confer strong resistance to the PMTV isolate from which the transgene sequence was derived and also to a second Scottish isolate. Plants of lines of the transgenic N. benthamiana were as resistant to two Swedish and two Danish PMTV isolates as to a Scottish isolate, and of five lines tested, greater than 93.5% of transgenic plants were immune. The coat protein gene sequences of these four Scandinavian isolates were very similar to those of the two Scottish isolates. The greatest divergence between the isolates was three amino acid changes and there was less than 2% change in CP gene nucleotide sequence. It is concluded that the PMTV CP transgene used in these experiments could confer resistance against isolates from different geographical areas because it is becoming apparent that the CP genes of PMTV isolates are highly conserved.     

Colonization of roots, stolons, tubers and stems of various potato (Solanum tuberosum) cultivars by the black-dot fungus Colletotrichum coccodes

In an attempt to better understand the importance of tuber-borne inoculum in black dot development, several potato cultivars were inoculated with various Colletotrichum coccodes isolates. Symptoms developed first on underground organs (starting 2 weeks after inoculation on roots, and later on stolons and tubers) of inoculated plants; stem infections developed only after 7–10 weeks, depending on the cultivar. Infection with C. coccodes resulted in a reduction in numbers of stolons and tubers in cv. Bintje, but not in the later maturing cv. Roseval. Significant isolate by cultivar interactions were detected from the analysis of root symptoms after inoculation of three potato cultivars (Bintje, Spunta and Desiree) with five C. coccodes isolates. Such an interaction was also detected for stolon/tuber symptoms at the latest scoring date (98 days after inoculation), but not at earlier dates (58, 70 and 84 days after inoculation). These results suggest that protocols based on root colonization might be used for investigating cultivar response to black dot and pathogenicity of C. coccodes isolates, and that some specificity exists in the reaction of potato genotypes to this pathogenic fungus.     

Mature plant resistance of potato against some virus diseases. II. Mature plant resistance and the influence of temperature on the ribosome and RNA content in leaves

Potato plants ‘Bintje’ were grown in growth chambers; one group of 27 plants at a daily regime of 15 h light and 9 h darkness with corresponding temperatures of 18 °C and 12°C, and a second group of 27 potato plants at a daily regime of 15 h light and 9 h darkness with corresponding temperatures of 22 °C and 17 °C. The plants of both groups were inoculated with potato virus X (PVX) 56 days after planting. Young leaves had a 3-fold higher ribosome and RNA content than ageing leaves. The decrease occurred earlier at 22 °C than at 18 °C. Although plants grown at 18 C produced smaller and fewer leaves than those grown at 22 C, the former produced a higher weight of tubers than those at the higher temperature. Although corresponding leaves of both groups showed considerable differences in ribosome and RNA contents, the rate of virus translocation to the tubers was equal in both groups. This can be explained by the different growth pattern.     

Direct tuber testing for Potato Y potyvirus by real‐time RT‐PCR and ELISA: reliable options for post‐harvest testing?*

The method currently used for testing potato tubers for viruses following harvest involves a growing‐on test. This takes up to 6 weeks to complete, and there is therefore a demand for more rapid test results. The sensitivity and reliability of direct tuber testing by DAS‐ELISA and real‐time RT‐PCR (TaqMan) were compared with the growing‐on test. In addition, the reliability of all three methods for the detection of Potato Y potyvirus (PVY) in tubers was compared over post‐harvest intervals of 6, 10, 14 and 18 weeks. The test material came from plots of tubers (cv. ‘Maris Piper’) containing a primary infection of strains PVY^N and PVY^O, following aphid transmission from marked infector plants grown during the 2003 season. Sample material was homogenized and divided, to provide comparative test material for detection of PVY by ELISA and real‐time RT‐PCR. Tuber eye‐plugs were then taken and subjected to the growing‐on test. The remainder of the tuber was also grown on and tested, to ensure infection was not missed as a consequence of an uneven distribution of virus throughout the tuber material. The results obtained using the two methods for direct testing of the tubers, and those results obtained from the traditional growing‐on test, are compared. The advantages and disadvantages of each method are discussed.     

Blackleg development and tuber yield in relation to numbers of Erwinia carotovora subsp. atroseptica on seed potatoes

The relationship between number of viable cells of Erwinia carotovora subsp. atroseptica on inoculated potato seed tubers and blackleg development was investigated in 2 years for five cultivars grown in the contrasting climates of Scotland and Israel. Blackleg, and to a lesser extent non-emergence, increased with higher numbers of bacteria on the seed tubers at planting. This relationship was also found for several commercial seed stocks of one cultivar naturally contaminated with different numbers of E. carotovora subsp. atroseptica.The threshold number of bacteria necessary for the development of blackleg declined during the growing season and was also higher for the cultivar Pentland Crown in comparison with the others. In general, yield declined linearly with blackleg incidence and there was a 0.8% reduction in yield for every 1 % blackleg at 13 weeks after planting. Yield loss was positively related to the incidence of blackleg late in the season, whereas the relationship between yield loss and the incidence of non-emergence was poor.     

湖南省马铃薯病毒病发生情况调查

为了解湖南省马铃薯种薯质量和主要病毒病发生情况,2019年-2020年马铃薯秋作和冬作期间,对长沙、益阳、湘潭、澧临等马铃薯生产区的155个马铃薯样品,运用反转录-聚合酶链式反应(RT-PCR)和双抗体夹心酶联免疫吸附检测(DAS-ELISA)技术,筛查6种主要马铃薯病毒,包括马铃薯X病毒Potato virus X(PVX)、马铃薯Y病毒Potato virus Y(PVY)、马铃薯M病毒Potato virus M(PVM)、马铃薯S病毒Potato virus S(PVS)、马铃薯A病毒Potato virus A(PVA)、马铃薯卷叶病毒Potato leaf roll virus(PLRV)。检测结果表明:6种马铃薯病毒病在湖南均有不同程度的发生,单一和两种病毒复合感染植株占比最高,其次是3种病毒复合感染,存在极少数植株复合感染4～5种病毒病情况。在秋作马铃薯中,PVY检出率达到29.41%;PVS和PVA检出率均为27.94%;PVM、PVX、PLRV的检出率分别为20.59%、19.12%、17.65%。在冬作马铃薯中,PVX检出率最高,达到31.03%;其次是PLRV,...     

Occurrence of the Andean strain of potato virus S in imported potato material and its effects on potato cultivars

Infection with potato virus S Andean (PVS^A) and ordinary (PVS^o) strains was found in potato breeder's selection No. 8163-511 imported from West Germany; the two PVS strains were differentiated by their reactions on Chenopodium quinoa Tests on potato leaf samples using enzyme-linked immunosorbent assay followed by inoculation to C quinoa were subsequently used to detect PVS^A and PVS^o in a large-scale survey of imported and domestic potato material. PVS^A was detected in breeders' selections and cultivars imported from the Netherlands and West Germany, but not in domestic certified seed potato stocks or farmers' once-grown stocks. PVS^o was found in both imported and domestic certified stocks, but infection was commoner in the imported ones. When plants of C. quinoa, C. amaranticolor, C. murale and Nicotiana debneyi were inoculated with four isolates of PVS^A, one induced mild symptoms while the reactions of the others ranged from moderate to severe. When plants of different potato cultivars were inoculated with three isolates, the plants were mostly infected without symptoms. However, when tubers from some were grown on, the progeny plants of most of the different combinations of cultivar and isolate of PVS^A developed one or more of the following symptoms: vein deepening, rugosity, interveinal chlorosis, premature senescence and early loss of lower leaves.