Aphid Transmission of Potato aucuba mosaic virus Strains Mediated by Different Strains of Potato virus Y

Three British strains of potato aucuba mosaic virus (PAMV) were tested for transmissibility by the aphid Myzus persicae. None was aphid transmissible on its own but all three were transmitted in the nonpersistent manner by aphids that had previously been fed on a source of the potyvirus potato virus Y (PVY). Different PVY strains mediated PAMV transmission from Nicotiana clevelandii to Capsicum annuum to different degrees, and different PAMV strains were transmitted at different frequencies when assisted by the same PVY strain. These results are compatible with the idea that subtle differences in the PAMV coat protein and in the PVY helper component are responsible for diffrences in frequencies of transmission of PAMV, without however, excluding the possibility of effects of other undefined factors. Transmission of PAMV was no less frequent when mediated by a PVY strain that was unable to infect C. annuum than when a C. annuum‐infecting PVY strain was used.     

Effect of mineral oil on Potato virus Y acquisition by Rhopalosiphum padi

Seed potato crops are currently sprayed weekly with mineral oil to prevent transmission of the Potato virus Y (PVY; Potyviridae: Potyvirus), one of the most prevalent and important non‐persistent viruses affecting potato production. In spite of its wide usage as inhibitor of virus transmission, the mode of action for mineral oil is poorly known. The objective of this study was to quantify the effect of dosage and time from application of mineral oil on the inhibition of PVY acquisition. The bird cherry‐oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), known as vector of PVY, was used in all the experiments. The results indicated that mineral oil efficiently decreased PVY acquisition by 75 and 70% 1 day after application of 5 and 10 l ha^?1, respectively. The inhibition effect decreased with time from application; mineral oil inhibits acquisition for less than 4 days at 5 l ha^?1 and between 8 and 12 days at 10 l ha^?1. As mineral oil was detected in the body of fewer aphids when they fed on plants 1 day after oil application, a change in the aphid probing behaviour on mineral oil‐treated plants was deduced. These results support the hypothesis that mineral oil physically inhibits the binding of the virus at the tip of the stylets.     

Information‐theory‐based model selection for determining the main vector and period of transmission of Potato virus Y

Potato virus Y (PVY, genus Potyvirus, family Potyviridae) is transmitted non‐persistently by aphids. It causes major losses in potato production (Solanum tuberosum), especially following seed tuber‐borne infection of plants. To limit the risk of PVY infection, seed potato production is located preferably in regions where vector pressure is low. The northern‐most high‐grade seed potato production area (HG zone) of Europe is in Finland. The aim of this study was to determine the incidence of aphid species with documented ability to transmit PVY and to use a modelling approach to determine their relative importance as vectors of PVY in the HG zone of Finland. Winged aphids were caught from six to seven potato fields in each of three growing seasons (2007–09) using yellow pan traps that were examined twice a week. Identification of more than 30 000 individuals indicated that 37% of the aphids belonged to nine species reported to transmit PVY. Incidence of PVY in seed lots was low (0–5.6%) and the seasonal increase of PVY incidence was also low in the potato crops. No potato‐colonising aphids were found on the plants in any of the years. The seasonal increase in PVY incidence was modelled using aphid counts in traps, the relative vector efficiencies of the aphids, virus resistance of cultivars, and the initial infection rate of the seed tubers as explanatory variables in generalised linear mixed modelling. Akaike's information criterion was employed to find the best set of explanatory variables for PVY in harvested tubers. Results of this modelling approach showed that the incidence of seed‐borne PVY infection and the early‐season vector flights are the most important factors contributing to the incidence of PVY in the yield. Compared to models with data from all potential vector species, models containing data from Aphis fabae only showed a better model fit with regard to the incidence of PVY in the harvested tubers. The explanatory power of the models was lost when A. fabae was omitted from the vector data, suggesting that other species play a negligible role as vectors of PVY in the HG zone of Finland. Results can be used to devise appropriate strategies for enhanced control of PVY.     

Efficacy of Three Strategies Based on Insecticide,Oil and Elicitor Treatments in Controlling Aphid Populations and Potato virus Y Epidemics in Potato Fields

Potato virus Y (PVY), the potato virus with the highest economic impact in Europe, is transmitted by aphids in a non‐persistent manner. A two‐year field experiment was conducted in Switzerland to evaluate the efficacy of three strategies for controlling aphid populations and the spread of PVY, consisting of treatment with one insecticide (Karate Zeon^®), one elicitor (Bion^®) and one oil (Telmion^®), respectively. The elicitor strategy proved to be ineffective for controlling aphid populations and inadequate for controlling PVY spread. The insecticide strategy gave incomplete protection from aphid infestations, owing to the selection of aphid‐resistant clones. The insecticide gave too little protection against PVY spread for it to be considered a suitable candidate for the purpose. The oil strategy had no effect on aphid populations, but was the best option to reduce PVY spread.     

The effect of pre-acquisition starvation on aphid transmission of potyviruses during observed and electrically recorded stylet penetrations

The effect of pre-acquisition starvation on stylet penetration behaviour by the aphidMyzus persicae (Sulz.) and the consequent non-persistent transmission of the potyviruses beet mosaic virus (BMV) and potato virus Y (PVY) were investigated. Visual observations indicated that starved aphids initiated penetrations earlier and penetrated for shorter periods than non-starved insects. Tethering with a fine gold wire did not affect these observations with either starved or non-starved aphids, but starvation caused increased PVY and BMV acquisition efficiency, regardless of tethering. Tethered aphids were then made part of an electrical circuit and their stylet activities investigated in detail. Electrically recorded aphids also acquired and inoculated both potyviruses more efficiently when starved, and these acquisitions and inoculations were associated with stylet punctures of plant cell membranes. However, starvation did not affect the occurrence of electrically recorded membrane puncture, suggesting that non-behavioural factors may contribute to the enhancement of virus transmission by pre-acquisition starvation.     

马铃薯Y病毒pipo基因的分子变异及结构特征分析

为揭示马铃薯Y病毒(Potato virus Y, PVY) pipo基因的分子变异和结构特征, 文章根据文献报道的马铃薯Y病毒属(Potyvirus) pipo 基因保守区序列设计一对简并引物, 从感染PVY的马铃薯病叶中克隆获得pipo基因的cDNA全长序列, 分析其核苷酸序列和氨基酸序列的特征, 并基于氨基酸序列使用贝叶斯法重建了Potyvirus的系统发育树。结果显示：20个PVY分离物成功扩增出预期大小(约235 bp)的特异性片段, 其核苷酸序列与已报道的其它PVY 株系的pipo基因核苷酸序列一致性均在92%以上; 5′端均含有典型的G1-2A6-7 基序(motif), 无碱基插入/缺失, 所有的核苷酸变异都是碱基置换, 共发现13个多态性位点, 其中4个简约信息位点, 9个单一变异位点, 表明该基因高度保守, 但不同分离物也存在一定的分子变异; PIPO蛋白理论等电点11.26~11.62, 无信号肽和跨膜区, 是可溶的亲水性蛋白; 整个蛋白含有3个保守区, 其中位于10~59aa的基序最为保守。该蛋白主要定位于线粒体中, 可能是线粒体导肽。系统发育分析结果显示, 源于PVY不同株系优先相聚成簇, 而向日葵褪绿斑驳病毒(Sunflower chlorotic mottle virus, SuCMoV)与辣椒重花叶病毒(Pepper severe mosaic virus, PepSMV)的亲缘关系较PVY相比更近, 与前人的结果相一致, 表明PIPO蛋白可以作为研究Potyvirus系统发育关系的新的分子标记。     

马铃薯Y病毒pl基因的克隆与序列分析

利用依据马铃薯Y病毒(PVY)pl基因序列设计合成的一对引物YP1,YP2,以带毒烟草总RNA为模板,通过RT-PCR方法扩增得到了0.83kb的目的条带,测序结果表明为PVY pl基因。通过对PVY P1蛋白氨基酸序列分析发现PVY不同分离物间P1蛋白氨基酸序列存在明显差异,氨基酸序列同源性在64％～94％间。依据P1蛋白氨基酸序列建立了PVY系统关系树并对PVY进行了类型分析。     

Potato virus Y Strain Spectrum in New Zealand – Absence of Recombinant N:O Strains

Potato virus Y (PVY) is a serious plant pathogen, causing severe yield losses worldwide on members of the Solanaceae, including potato, pepper, tomato and tobacco. During the last two decades new virus strains have been detected, including those representing recombinants between N- and O-strains, now designated PVY^NTN and PVY^N-Wilga, respectively. The question of whether recombination is easily induced in nature by mixed infections of potato might be answered by an investigation of strains appearing under isolated conditions such as those in New Zealand. More than 30 PVY isolates collected during the last 20 years were characterized biologically, serologically and using molecular biological approaches. The New Zealand population of PVY isolates was mainly composed of PVY^N and PVY^O. To date no recombinant strains have been found among the isolates tested. Similarly, experiments performed with these isolates on potatoes under greenhouse conditions with mixed infection PVY^N/PVY^O did not result in signs of recombination. This raises the question as to the driving force for the appearance of recombinant strains. It also demonstrates the efficacy of plant quarantine measures in New Zealand over the past 20 years.     

全基因组序列的系统发育与重组分析鉴定我国马铃薯Y病毒株系

为明确我国马铃薯Y病毒(Potato virus Y,PVY)株系组成及其在不同寄主上的分布特征,文章对31条PVY中国分离物的基因组编码区进行了系统发育及重组分析。系统发育分析结果显示,最大似然法(maximum likelihood,ML)和邻接法(neighbor-joining,NJ)重建的系统发育拓扑结构基本一致,GF_YL20、FZ10、DF、SD1、1116和9703-3等6个分离物均未与已知株系相聚,其他株系来源相同的分离物以较高的自展值相聚成簇,显示出较强的株系特异性。重组分析显示,31个PVY分离物中,共有28个PVY分离物均检测到具有显著的重组信号,这些分离物主要包括PVY~(N-Wi)、PVY~(NTN)和PVY~(NTN-NW)三种株系。进一步分析显示,分离物1104、DF、SD1、1116和9703-3为未报道过的PVY新重组分离物。株系统计结果显示PVY重组株系已上升为优势株系,生产上需要密切注意这些株系,尤其新重组分离物的发展动态。以上结果表明,综合应用PVY全基因组序列的系统发育和重组分析,可以实现PVY株系的准确鉴定。     

Effects of the pyrethroid deltamethrin on the acquisition and inoculation of viruses by Myzus persicae

The pyrethroid, deltamethrin, alone or as an emulsifiable formulation, hindered infection of healthy plants with the persistent beet mild yellowing virus (BMYV) and both acquisition of, and infection with, the non-persistent potato virus Y (PVY) and the semi-persistent sugar beet yellows virus (BYV) by Myzus persicae in glasshouse tests.
Another pyrethroid, RU-15525, also protected against infection with PVY. Even sub-lethal amounts of deltamethrin decreased virus transmission by rapidly incapacitating the aphids, the effect being least with aphids most resistant to organophosphorous insecticides and to certain pyrethroids including deltamethrin. Demeton-S-methyl hindered infection only with BMYV. This work shows that deltamethrin restricts transmission of persistent, semi-persistent and perhaps more importantly of non-persistent viruses in the glasshouse, and has potential for doing the same in the field.     

Molecular Analysis of the Coat Protein of Potato virus Y Isolates in Greece Suggests Multiple Introduction from Different Genetic Pools

The phylogenetic relationships among Potato virus Y (PVY) isolates from northern and southern Greece were investigated. A large part of coat protein gene of 49 tobacco isolates and three from pepper was examined. The analysis showed that all 52 isolates consisted of 34 distinct haplotypes, with only one haplotype found in both northern and southern regions. The southern population was more diverse than that from the north. The phylogenetic analyses of the Greek haplotypes alone or in combination with isolates from other countries using the maximum likelihood method classified unambiguously almost all the haplotypes examined. Nine tobacco haplotypes from the south were classified as C‐like (particularly C1), whereas 22 haplotypes from tobacco and two from pepper from both north and south were classified as N‐like. One tobacco haplotype from the south was found recombinant between N‐like and C1 lineages. The pattern of molecular evolution was examined using the fixed‐effects likelihood and the single‐likelihood ancestor counting methods. The analysis indicated that the evolution of PVY isolates appeared to be conservative (purifying selection and neutral evolution). These findings are discussed in relation to the introduction of PVY in the tobacco crop in Greece and the between region dispersal. A scenario of multiple introductions of PVY isolates in north and south Greece from different genetic pools and low or nil between region spread of the virus isolates was proposed.     

不同寄主来源的马铃薯Y病毒群体遗传结构的比较分析

文章以马铃薯Y病毒(Potato virus Y, PVY) P3和pipo基因为分子标记,比较分析烟草和马铃薯两个寄主的PVY遗传多样性和群体分化,并评估突变、选择、基因流等遗传力所起的作用。通过P3和pipo基因计算获得的烟草和马铃薯群体分化指数F_ST分别为0.116和0.120,且统计检验差异显著,表明烟草和马铃薯寄主的PVY之间中度分化。变异分析结果显示,烟草分离物P3和pipo基因的核苷酸序列一致性分别为85.2%~100%和76.5%~100%,而马铃薯分离物的P3和pipo基因的核苷酸序列一致性分别为95.7%~100%和93.0%~100%,表明烟草PVY变异程度高于马铃薯。同时,P3基因内检测到大量的净化选择位点,表明该基因大部分位点的变异为有害突变,在进化过程中被剔除。此外,P3基因内还检测到两个显著正向选择位点,表明这两个位点的变异为有益突变,有利于病毒的生存竞争。在pipo基因中未检测到显著的选择位点,表明该基因上的变异基本不受自然选择影响。通过P3和pipo基因计算烟草和马铃薯群体间的基因流Nm值分别为1.91和1.83,表明这两个群体间存在较强的基因交流。以上结果表明,来源于烟草和马铃薯寄主的PVY遗传差异显著,突变、自然选择以及基因流都影响两者的遗传多样性及遗传分化程度。     

Expression of Potato Virus Y Coat Protein Gene in Transgenic Potato

Potato virus Y (PVY) N coat protein (CP) coding sequence was cloned into a plant expression vector pMON316 under the CaMV 35S promoter. Leaf discs of potato (Solanum tuberosum) were used to Agrobacterium-mediated gene transfer. A large number of regenerated putative transgenic plants were obtained based on kanamycin resistance. Using total DNA purified from transgenic plants as templates and two oligonucleotides synthesized from 5' and 3' of the PVY coat protein gene as primers, the authors carried out polymerase chain reaction (PCR) to check the presence of this gene and obtained a 0. 8 kb specific DNA fragment after 35 cycles of amplification. Southern blot indicated that the PCR product was indeed PVY CP gene which had been integrated into the potato genome. Enzyme-linked immunosorbent assay (ELISA) of our transgenic plants showed that CP gene was expressed in at least some transgenic potato plants.     

Engineering virus resistance using a modified potato gene

Natural mutations in translation initiation factor eIF4E confer resistance to potyviruses in many plant species. Potato is a staple food crop plagued by several potyviruses, yet to date no known eIF4E-mediated resistance genes have been identified. In this study, we demonstrate that transgenic expression of the pvr1(2) gene from pepper confers resistance to Potato virus Y (PVY) in potato. We then use this information to convert the susceptible potato ortholog of this allele into a de novo allele for resistance to PVY using site-directed mutagenesis. Potato plants overexpressing the mutated potato allele are resistant to virus infection. Resistant lines expressed high levels of eIF4E mRNA and protein. The resistant plants showed growth similar to untransformed controls and produced phenotypically similar tubers. This technique disrupts a key step in the viral infection process and may potentially be used to engineer virus resistance in a number of economically important plant-viral pathosystems. Furthermore, the general public may be more amenable to the 'intragenic' nature of this approach because the transferred coding region is modified from a gene in the target crop rather than from a distant species.     

Characterization of Viruses Infecting Potato Plants from a Single Location in Shetland,an Isolated Scottish Archipelago

Sequence data were obtained from 29 isolates of Potato virus A (PVA), Potato virus S (PVS), Potato virus V (PVV) and Potato virus X (PVX) infecting nine tubers from Shetland, one of the most remote inhabited islands in the United Kingdom. These isolates were sequenced in the coat protein region, as were 29 Scottish mainland isolates of the same four potato virus species, and these 58 isolates were compared to previously published sequence data. This has allowed the characterization of viruses from a relatively isolated location, where there is little production of ware potatoes and no seed potato production. Phylogenetic homogeneity of the Shetland isolates of PVS and PVV was apparent. PVX was more heterogeneous, and Shetland isolates cluster with the Scottish isolates in a group which includes Asian and European isolates. For PVA, the majority of the Shetland and Scottish mainland isolates formed a predominantly Scottish grouping, with the remaining Shetland and Scottish mainland isolates clustering with a previously characterized Scottish isolate. There were three main groups of PVA, of which the Scottish grouping was the only one which did not have a fully characterized representative. To extend the characterization of PVA, the nucleotide sequence of the full polyprotein region encoding all the gene products of an isolate from Shetland was determined.