Control of potato virus Y (PVY) in seed potatoes by oil spraying,straw mulching and intercropping

Potato virus Y (PVY) is the potato virus with the highest economic impact on seed potato production. Insecticides are efficient in controlling aphids, which are the vectors of this virus, but rarely limit virus spread in the field. Straw mulching and mineral oil spraying are known as alternatives to insecticides to reduce PVY incidence, but important year‐to‐year variation in efficacy has been observed with both of these techniques. Preliminary studies revealed the efficacy of intercropping in controlling PVY spread, but more data are needed to validate this observation. A four‐year field trial was conducted in Switzerland to assess the potential synergistic effect of combining mineral oil spraying with straw mulching to increase the protection of seed potato crops against PVY spread. Furthermore, the efficacy of intercropping with oat and hairy vetch was examined as a novel way to control in‐field PVY spread. The present work demonstrates that the modes of action of mineral oil and straw mulching are complementary and reduce the year‐to‐year variation observed with oil and straw when used alone as PVY control agents. The results also demonstrate the efficacy of intercropping for the control of PVY, and the mode of action of this novel control method is discussed. Overall, this work shows that it is possible to increase the protection of potato fields against PVY spread by combining control strategies with different modes of action that complement each other, such as mulching, oil spraying and intercropping.     

矿物油和维生素B1对马铃薯病毒病的防效研究

多数马铃薯病毒可以借助蚜虫传播, 并通过块茎世代积累, 导致马铃薯种性退化, 严重影响块茎的产量和品质?为了筛选新型?环保的马铃薯病毒病防治药剂, 本研究通过3个季节的田间试验, 对矿物油?维生素B1和杀虫剂吡虫啉在防治马铃薯病毒病中的效果进行了评价?结果表明, 通过马铃薯出苗后间隔10 d连续3次喷施, 矿物油能够控制马铃薯卷叶病(potato leaf-roll virus, PLRV)的发生, 对马铃薯M病毒(potato virus M, PVM)和马铃薯S病毒(potato virus S, PVS)的平均防效也分别达到66.72%和70.40%, 但对马铃薯Y病毒(potato virus Y, PVY)和马铃薯A病毒(potato virus A, PVA)在不同的年份和季节的防效不稳定, 平均防效为27.34%和65.02%?维生素B1对PLRV?PVM和PVS的防效也比较明显, 分别达83.36%?83.33%和73.32%, 而对PVY同样防效不稳定, 对PVA防效不明显?杀虫剂吡虫啉对PLRV?PVS和PVM的防效也不稳定, 且对PVY和PVA的防效均不显著?本研究中马铃薯X病毒(potato virus X, PVX)发生频率极低, 未进行病毒病的防效比较?综上所述, 矿物油和维生素B1对马铃薯主要病毒病的综合防效较吡虫啉好, 同时它们的增产效果更明显, 产投比高于化学药剂, 值得推广?     

马铃薯Y病毒在种薯中检出率及其株系鉴定

 马铃薯是我国重要粮食和经济作物。马铃薯Y病毒(potato virus Y,PVY)是危害马铃薯生产的重要病害。种植脱毒种薯是防治PVY最有效的途径。马铃薯种薯携带PVY问题严重,但种薯中PVY株系还不清楚。本研究利用PVY特异性抗体检测了7个马铃薯品种362个种薯,发现不同品种种薯带毒率差异较大,最高达12%。通过RT-PCR方法扩增获得了7个PVY分离物编码区全序列。重组分析发现7个分离物基因组均为重组型,根据重组位点的差异可以分为PVY^NTN-NW(SYR-II型)、Rec-1、Rec-2和Rec-3等4种重组类型,后3种为新重组类型。系统进化分析发现,分离物HQH18G3-10与PVY^NTN-NW(SYR-II型)处于同一个大的分支,但与中国PVY大田分离物聚集在一起形成一个相对独立的组,命名为PVY^NTN-NW(CN型);其余6个分离物与数据库中的中国分离物聚集在PVY^N-Wi组。这暗示PVY中国分离物具有相对独立的进化过程,PVY马铃薯大田分离物和种薯分离物进化上相近。所有分离物均能在珊西烟上引起典型叶脉坏死症状,HQH18G3-10引起的坏死症状最为严重。本研究首次报道了我国种薯内PVY发生情况,对分析病毒发生发展规律和防控具有借鉴作用。     

马铃薯Y病毒在种薯中检出率及其株系鉴定

马铃薯是我国重要粮食和经济作物。马铃薯Y病毒(potato virus Y,PVY)是危害马铃薯生产的重要病害。种植脱毒种薯是防治PVY最有效的途径。马铃薯种薯携带PVY问题严重,但种薯中PVY株系还不清楚。本研究利用PVY特异性抗体检测了7个马铃薯品种362个种薯,发现不同品种种薯带毒率差异较大,最高达12%。通过RT-PCR方法扩增获得了7个PVY分离物编码区全序列。重组分析发现7个分离物基因组均为重组型,根据重组位点的差异可以分为PVY^NTN-NW(SYR-II型)、Rec-1、Rec-2和Rec-3等4种重组类型,后3种为新重组类型。系统进化分析发现,分离物HQH18G3-10与PVY^NTN-NW(SYR-II型)处于同一个大的分支,但与中国PVY大田分离物聚集在一起形成一个相对独立的组,命名为PVY^NTN-NW(CN型);其余6个分离物与数据库中的中国分离物聚集在PVY^N-Wi组。这暗示PVY中国分离物具有相对独立的进化过程,PVY马铃薯大田分离物和种薯分离物进化上相近。所有分离物均能在珊...     

A novel type of Potato virus Y recombinant genome,determined for the genetic strain PVYE

Two Potato virus Y (PVY) isolates collected in Brazil, PVY‐AGA and PVY‐MON, were identified as recombinants between two parent genomes, PVY^NTN and PVY‐NE‐11, with a novel type of genomic pattern. The new recombinants had an ordinary PVY^NTN genome structure for approximately 6·7‐kb from the 5′‐end of the genome whereas the 3′‐terminal 3·0‐kb segment had two fragments of NE‐11‐like sequence separated by another small PVY^NTN‐like fragment. PVY strains are defined based on the hypersensitive resistance (HR) response in potato indicators. Both PVY‐AGA and PVY‐MON isolates did not induce the HR in potato cultivars carrying Ny, Nc, or (putative) Nz genes and thus were able to overcome all known resistance genes to PVY. Only one of the two isolates, PVY‐AGA, induced a vein necrosis reaction in tobacco. The biological responses of the potato indicators and tobacco defined PVY‐MON as an isolate of the PVY^E strain. To distinguish PVY‐AGA and PVY‐MON from other PVY^NTN isolates, an RT‐PCR test was developed utilizing new specific primers from the capsid protein gene area and producing a characteristic 955‐bp band. Serological profiling of these PVY isolates with three monoclonal antibodies revealed an unusual reactivity, where one of the two commercial PVY^N‐specific monoclonal antibodies did not recognize PVY‐AGA. The ability of these new PVY recombinants to overcome resistance genes in potato producing mild or no symptoms, combined with the lack of serological reactivity towards at least one PVY^N‐specific antibody may present a significant threat posed by these isolates to seed potato production areas.     

Occurrence of Potato virus Y strain PVYNTN in foundation seed potatoes in Japan,and screening for symptoms in Japanese potato cultivars

In 2008 and 2009 seasons, a sudden increase in Potato virus Y (PVY) incidence was recorded in foundation seed potatoes in Hokkaido, northern Japan. This increase was obvious during the field inspection and the postharvest indexing. Molecular typing revealed that besides the previously reported strains of PVY^O and PVY^NA‐N, the most common strain identified was the recombinant PVY^NTN, with three characteristic recombinant junctions at the HC‐Pro, VPg and CP regions. No potato tuber necrotic ringspot disease (PTNRD) was observed in foundation seed potatoes in correlation with the presence of PVY^NTN. Moreover, an isolate with a typical PVY^NTN recombinant genome, namely Eu‐12Jp, did not induce PTNRD in 62 Japanese potato cultivars tested in both primarily and secondarily infected plants. Two cultivars carrying the extreme resistance gene Ry_chc were resistant to the infection with Eu‐12Jp, which presents potential sources of resistance to PVY^NTN. Eu‐12Jp induced systemic mottle in potato cultivars Desiree and King Edward carrying resistance genes Ny and Nc, respectively, but induced a hypersensitive reaction in potato cultivar Maris Bard, with the Nz hypothetical resistance gene typical of the PVY^Z strain group. Therefore, based on the genome structure and the reaction of the potato N resistance genes, Eu‐12Jp should be classified as PVY^Z‐NTN, as described for isolates from Idaho, USA recently. This is the first report of PVY^Z‐NTN in Japan and the sudden and increased occurrence of PVY^NTN/PVY^Z‐NTN represents a potential risk of PTNRD developing and increases the significance of PVY in Japan.     

Use of oils combined with low doses of insecticide for the control of Myzus persicae and PVY epidemics

Experiments were carried out in the laboratory to assess the insecticidal effect on Myzus persicae Sulzer of different oils applied alone or combined with imidacloprid or pirimicarb. The oils tested were a horticultural mineral oil, a refined rapeseed oil, a refined soya oil and a raw fish oil. When the oils were sprayed alone on pepper plants infested with M. persicae, mineral oil caused the highest mortality of aphids (over 80%). Applied before aphid infestation of pepper leaves and in mixture with low doses of imidacloprid (at one-fifth of the dose recommended by the manufacturer) and pirimicarb (at one-tenth of the dose recommended by the manufacturer), the oils did not significantly increase the toxicity of the insecticides alone. However, sprayed on aphid-infested pepper plants, the mortality rates achieved by imidacloprid/mineral oil and imidacloprid/rapeseed oil mixtures were significantly higher than those achieved by imidacloprid alone at 16 and 24 h. In a field experiment the effect on the incidence of the potato virus (PVY) of the oils in combination with imidacloprid was determined. Mineral oil, rapeseed oil and soya oil were sprayed eight times onto seed potato plants treated with imidacloprid before sowing. Mineral oil reduced PVY-infected plants by 60% and rapeseed oil by 40% compared with plots treated with imidacloprid. The oils applied as 10 ml litre-1 emulsions in water did not cause symptoms of phytotoxicity on the potato plants, and yield was not reduced.     

Dickeya species: an emerging problem for potato production in Europe

Dickeya species (formerly Erwinia chrysanthemi) cause diseases on numerous crop and ornamental plants world‐wide. Dickeya spp. (probably D. dianthicola) were first reported on potato in the Netherlands in the 1970s and have since been detected in many other European countries. However, since 2004–5 a new pathogen, with the proposed name ‘D. solani’, has been spreading across Europe via trade in seed tubers and is causing increasing economic losses. Although disease symptoms are often indistinguishable from those of the more established blackleg pathogen Pectobacterium spp., Dickeya spp. can initiate disease from lower inoculum levels, have a greater ability to spread through the plant’s vascular tissue, are considerably more aggressive, and have higher optimal temperatures for disease development (the latter potentially leading to increased disease problems as Europe’s climate warms). However, they also appear to be less hardy than Pectobacterium spp. in soil and other environments outside the plant. Scotland is currently the only country in Europe to enforce zero tolerance for Dickeya spp. in its potato crop in an attempt to keep its seed tuber industry free from disease. However, there are a number of other ways to control the disease, including seed tuber certification, on‐farm methods and the use of diagnostics. For diagnostics, new genomics‐based approaches are now being employed to develop D. dianthicola‐ and ‘D. solani’‐specific PCR‐based tests for rapid detection and identification. It is hoped that these diagnostics, together with other aspects of ongoing research, will provide invaluable tools and information for controlling this serious threat to potato production.     

Aerial electrostatic‐charged sprays for deposition and efficacy against sweet potato whitefly (Bemisia tabaci) on cotton

Background: The efficacy of aerial electrostatic‐charged sprays was evaluated for spray deposit characteristics and season‐long control of sweet potato whitefly (SWF), Bemisia tabaci Genn. biotype B (aka B. argentifolii Bellows & Perring), in an irrigated 24 ha cotton field. Treatments included electrostatic‐charged sprays at full and half active ingredient (AI) label rate, uncharged sprays and conventional sprays applied with CP nozzles at full label rate with several different insecticides. Results: Spray droplet size was significantly smaller for electrostatic‐charged sprays than for conventional sprays in top‐ and mid‐canopy locations. The seasonal mean numbers of viable eggs and live large nymphs on cotton treated with electrostatic‐charged sprays were comparable with those on cotton treated with conventional applications. Lethal concentration (LC₅₀) for adults for electrostatic‐charged sprays was comparable with that for conventional sprays. Conclusion: The amenability of electrostatic‐charged sprays to a wide array of pesticides with different chemistries should be a useful tool in combating insect resistance. Results reported here suggest that the potential exists for obtaining increased efficacy against whiteflies using an electrostatic spray charging system, and that additional research will be required to improve charge‐to‐mass (Q/M) ratio in order to increase deposition of pest control materials to the lower surfaces of cotton leaves where the whiteflies reside. Copyright © 2009 Society of Chemical Industry     

基于小RNA深度测序和RT-PCR检测侵染广东省冬种马铃薯的病毒

为明确侵染广东省冬种马铃薯的病毒种类及优势病毒,结合小RNA深度测序技术及RTPCR检测方法,对采集于广东省冬种马铃薯7个主产区的189份疑似病样进行检测分析。结果表明,经小RNA深度测序技术检测马铃薯病毒病混合样,发现存在马铃薯Y病毒(Potato virus Y,PVY)、马铃薯S病毒(Potato virus S,PVS)和马铃薯卷叶病毒(Potato leaf-roll virus,PLRV)3种病毒。进一步设计3种病毒的特异性引物并利用国内已报道的其它5种马铃薯病毒的特异性引物进行RT-PCR检测,发现189份马铃薯病毒病疑似病样中仅检测到PVY、PVS和PLRV这3种病毒,检出率依次为75.13%、10.05%和4.76%,且3种病毒在马铃薯上还存在复合侵染,复合侵染率为14.19%,其中PVY在各马铃薯产区均可检测到。表明侵染广东省冬种马铃薯的病毒为PVY、PVS和PLRV,其中PVY是优势病毒。     

Seed transmission of Sweet potato leaf curl virus in sweet potato (Ipomoea batatas)

Sweet potato leaf curl virus (SPLCV) infects sweet potato and is a member of the family Geminiviridae (genus Begomovirus). SPLCV transmission occurs from plant to plant mostly via vegetative propagation as well as by the insect vector Bemisia tabaci. When sweet potato seeds were planted and cultivated in a whitefly‐free greenhouse, some sweet potato plants started to show SPLCV‐specific symptoms. SPLCV was detected by PCR from all leaves and floral tissues that showed leaf curl disease symptoms. More than 70% of the seeds harvested from SPLCV‐infected sweet potato plants tested positive for SPLCV. SPLCV was also identified from dissected endosperm and embryos. The transmission level of SPLCV from seeds to seedlings was up to 15%. Southern blot hybridization showed SPLCV‐specific single‐ and double‐stranded DNAs in seedlings germinated from SPLCV‐infected seeds. Taken altogether, the results show that SPLCV in plants of the tested sweet potato cultivars can be transmitted via seeds and SPLCV DNA can replicate in developing seedlings. This is the first seed transmission report of SPLCV in sweet potato plants and also, to the authors' knowledge, the first report of seed transmission for any geminivirus.     

Reduction of yield losses in pepper crops caused by potato virus Y in KwaZulu-Natal,South Africa,using plastic mulch and Yellow sticky traps

Potato virus Y is the major cause of crop losses in pepper in KwaZulu-Natal Province, South Africa. An evaluation of the efficacy of five treatments to reduce transmission of the virus to pepper by aphids was conducted. The use of white plastic mulch was the most effective, resulting in a 32% yield increase over the untreated control. Yellow sticky plastic traps also had a significant beneficial effect on the yield, but mineral oil sprays as well as a neem-derived product were ineffective. Weekly mercaptothion (malathion) sprays caused an increase in virus incidence, and yields were only 49% that of the untreated control.     

Possible induction of potato plant defences against <Emphasis Type="Italic">Potato virus Y</Emphasis> by mineral oil application

In recent decades, mineral oil spray has been considered an effective means to reduce aphid-mediated spread of non-persistent viruses such as Potato virus Y (PVY). However, the mechanism by which mineral oil prevents viral outbreaks is not well-characterized. Despite the fact that several studies have investigated the effects of mineral oil on aphid feeding behaviour, vector fitness and virus attachment to vector mouthparts, the effect of oil treatment on the plant response has not been studied. To address this need, the current study has assessed the impact of Vazyl-Y mineral oil on the plant-vector-virus (i.e. potato-aphid-PVY) pathosystem in potato, with a particular focus on the plant response. These results show for the first time that oil treatment induces the expression of plant-virus interaction related genes in both local and systemic non-infected tissues, as well as in PVY-infected plants. Finally, the oil’s elicitation properties in reducing viral infectivity are discussed.     

Effect of temperature on resistance to Potato virus Y in potato cultivars carrying the resistance gene Rychc

The effect of cultivation temperatures on the resistance reaction to three Potato virus Y strains (PVY^O, PVY^N and PVY^NTN) in potato cultivars carrying Ry_chc was examined. When potato plants carrying Ry_chc were cultivated at 22 °C, a few small necrotic spots developed on inoculated leaves by 5 days after mechanical inoculation (dpi), and systemic infection of a few symptomless plants was confirmed at 28 dpi by IC‐RT‐PCR. At 28 °C, distinct necrotic spots developed on inoculated leaves by 5 dpi, and systemic symptoms occasionally appeared at 28 dpi. Thus, high temperature weakens Ry_chc‐conferred resistance. However, the incidence of systemic infection and the titre of virus in resistant cultivars at 28 °C were lower than in a susceptible cultivar. In graft inoculation under high summer temperatures, some plants developed necrosis on the leaves and stem, but PVY was barely detected by RT‐PCR in leaves on potato carrying Ry_chc. When seedlings from progeny tubers of plants that were inoculated with PVY and grown in a greenhouse at >30 °C in the daytime were examined by ELISA and IC‐RT‐PCR, PVY was not detected in cultivars carrying Ry_chc. These results show that Ry_chc confers an extreme resistance to PVY strains occurring in Japan.     

Characteristics of infestation of sweet potato by sweet potato weevil Cylas formicarius (Coleoptera: Apionidae)

Studies were conducted to examine the characteristics of infestation of vines of sweet potato plants by the sweet potato weevil, Cylas formicarius (F.). The use of terminal tender vine cuttings, taken even from heavily weevil‐infested sweet potato, to grow a new crop and planting such a crop in plots surrounded by barriers to reduce weevil migration from the outside to the newly planted area, produced a practically weevil‐free crop. On the contrary, crop planted to old vine cuttings in an open field was severely damaged by the weevil. Consequently, crop planted using tender vine cuttings produced significantly more root yield than the one planted to old vine cuttings, irrespective of whether the planting was done in an open field or in an insect‐protected field. Sweet potato weevil infestation of 1‐ to 8‐week‐old plants increased significantly with plant age. The insect preferred sweet potato roots over sweet potato vines when both plant parts were available for infestation. Dipping the vine cuttings for 30 min in carbofuran solution prior to planting protected the newly planted sweet potato crop for up to 6 weeks after planting.     

Virus transmission by aphids in potato crops

This paper reviews the contribution of vector activity and plant age to virus spread in potato crops. Determining which aphid species are vectors is particularly important for timing haulm destruction to minimize tuber infection by potato virus Y (PVY). Alate aphids of more than 30 species transmit PVY, and aphids such asRhopalosiphum padi, that migrate in large numbers before flights of the more efficient vector,Myzus persicae, appear to be important vectors. Differences in methodology, aphid biotypes and virus strains prevent direct comparisons between estimates of vector efficiencies obtained for aphids in different countries in north western Europe. M. persicae is also the most efficient vector of potato leafroll virus (PLRV), but some clones ofMacrosiphum euphorbiae transmit PLRV efficiently toNicotiana clevelandii and potato test plants. The removal of infected plants early in the season prevents the spread of PLRV in cool regions with limited vector activity. The proportion of aphids acquiring PLRV from infected potato plants decreases with plant age, and healthy potato plants are more resistant to infection later in the season. Severe symptoms of secondary leafroll developed on progeny plants of cv. Maris Piper derived from mother plants inoculated with PLRV in June or July of the previous year. Progeny plants derived from mother plants inoculated in August showed only mild symptoms, but the concentration of PLRV in these plants was as high as that in the plants with severe symptoms.     

Control of air-borne field spread of tulip breaking virus,lily symptomless virus and lily virus X in lilies by mineral oils,synthetic pyrethroids,and a nematicide in the Netherlands

The inhibitory effect on the spread of viruses in lilies viz., tulip breaking virus (TBV; nonpersistently aphid-borne, potyvirus,) lily symptomless virus (LSV; non-persistently alphidborne, carlavirus), and lily virus X (LVX; potexvirus of unknown etiology), was studied of brands of mineral oil (Luxan oil H and Duphar-7E oil) and synthetic pyrethroid insecticides (l-cyhalothrin and deltamethrin), and a nematicide (aldicarb) in crops in which virus-infected plants were present as virus sources. The spread of TBV and LSV were controlled by sprays of mineral oil and insecticide, while that of LSV was also limited by the soil-applied nematicide. The spread of LVX was reduced by the insecticides and, not effectively by the mineral-oil spraying, by which data the mode of transmission may be presumed to be by an insect in the persistent or semi-persistent manner.Mixtures of mineral oil and pyrethroid were more effective in the reduction of spread of TBV and LSV than either components tested alone. The mineral oil was the most effective component in the mixtures in which pyrethroid added a slight extra effect. The addition of pyrethroid did not mask either the lower efficacy of the oil brand Duphar-7E oil, or the diminished inhibitory effect of low dosages of oil. The normal rate of mineral oil gave similar control to that of a mixture of mineral oil at half rate plus the pyrethroid at full dosage. Low rates of oil, or even synthetic pyrethroids alone may be used on cultivars which suffer of the loss of bulb weight by the use of normal or decreased rates of oil. Weekly sprays were more effective than fortnightly sprays. The rate of control by the weekly sprays ranged between 90 and 95% for Luxan oil H at half dosage plus the full rate of pyrethroid. Weekly sprayed synthetic pyrethroids alone onto the virus sources and the plants to be infected gave 60–70% control. The weight ratios tended to be slightly reduced if the half dosage of the efficient Luxan oil H was used. Factors which affect the control of the air-borne field spread of viruses by mineral oils and synthetic pyrethroid insecticides in lilies are discussed.     

Progress in aphid forecasting systems

Potato virus Y and many other viruses of potatoes cause major economic losses to seed potato production in many countries. Potato virus Y, which is transmitted in a non-persistent manner, is one of the most important virus diseases of potatoes in many countries in Europe and especially in the northern regions.During the last decade there has been an increasing interest in developing methods for potato virus forecasting. The abundance of virus vectors is often estimated by yellow water traps (YWT), suction traps or field surveys. In Sweden the relationship between occurrence of alate aphids and the proportion of PVY infected progeny tubers has been studied since 1975. A dynamic simulation model for PVY has been designed for predicting the incidence of PVY. The simulation model describes a system which includes e.g., healthy and PVY diseased potato plants, different aphid species as virus vectors an their efficiency as virus vectors, the susceptibility of the potato crop according to mature plant resistance and date of haulm destruction. There was a good correlation between model output and samples of progeny tubers tested for PVY.