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     

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.     

Environmental factors influencing aphid transmission of potato virus Y and potato leafroll virus

Summary The effect of temperature, relative humidity (RH) and light on aphid transmission of potato virus Y (PVY) and potato leafroll virus (PLRV) was studied using as vectorsMyzus persicae Sulz. andAphis gossypii Glov. Host susceptibility was enhanced by 48 h pre-inoculation exposure at 25°C and by 48 h post-inoculation exposure to 30°C. High RH (80%) in both pre- or postinoculation phases enhanced host susceptibility. Continuous fluorescent light (4000 lux) did not alter the rate of transmission of either virus. High RH (80–90%) and high temperature (25–30°C), when combined, increased virus transmission by 30–35%. Transmission rates were reduced by nearly 50% if RH was maintained at 50% in either of the two phases even if the temperature was 25 or 30°C. Both viruses were acquired by aphids earlier (13–20 days after inoculation) when the source plants were incubated at 25 or 30°C. Most virus was transmitted from plants inoculated with PVY 13 to 16 days and with PLRV 15 to 20 days previously. Transmission rates of PVY were enumerated from symptom expression on test plants and by Enzyme Linked Immunosorbent Assay (ELISA) whereas those of PLRV were enumerated from symptom expression alone.     

How Long can Rogued Potato Plants Left in the Field Be a Source of <Emphasis Type="Italic">Potato Virus Y</Emphasis> for Aphids?

Removal of diseased plants (roguing) is commonly practiced in seed potato production. Diseased plants left to desiccate in fields could possibly serve as sources of Potato virus Y (PVY). PVY acquisition by three aphid species (Myzus persicae, Rhopalosiphum padi, Aphis fabae) was evaluated with leaflets from rogued plants for seven days. Results showed greater PVY acquisition rates in non-colonizing aphids species compared to colonizing ones. The proportion of aphids leaving leaflets increased with time (i.e. days after plants were uprooted) and some aphids were carrying PVY in their stylets on each of the seven days of the experiment, suggesting that aphids were able to probe and acquire PVY even when plants wilted. These results confirmed that diseased plants left in fields can serve as a source of PVY for aphids even after they wilted and emphasises that proper actions must be taken to efficiently remove diseased plants from fields.     

Control of aphid-borne potato virus Y in potatoes with oil emulsions

Tests were made at Presque Isle, Maine, from 1963 through 1965 to measure the effect of oil sprays on the spread of potato virus Y (PVY) in Green Mountain potatoes. In 1963, 4 weekly applications of a 1% mineral oil emulsion at 1.25 gal oil/acre(4.71/.41 ha) did notaffect significantly (P = 0.05) the spread of PVY. In 1964, the 64% control of PVY spread from 5 weekly applications of mineral oil emulsion at 1.25 gal/acre was not significantly different at that level from the 55% control from 5 weekly applications of the oil emulsion at 2.5 gal/acre (9.5 1/.41 ha). Three or 5 weekly applications of an alkylated naphthalene (Velsicol AR-60®) spray at 1.25 gal/acre significantly increased spread of PVY compared to that from 5 applications of the oil at 1.25 or at 2.5 gal/acre. In 1965, from 69 to 75% control of PVY spread resulted from 6 weekly applications of a paraffin oil emulsion at 2.5 gal/acre. The percent spread from the 6 weekly applications was smaller, but not significantly so (P = 0.05), than from 3 weekly applications made during the first half of the same 6-week period. In these tests, relatively light spread of PVY occurred, and control of spread was rather variable but the results indicate that oil emulsion sprays offer promise for protecting potato plants from PVY infection.     

Soybean aphid,Aphis glycines Matsumura, a new vector ofPotato virus Y in potato

Soybean aphid (Aphis glycines Matsumura), an exotic species first discovered in the North Central region of the United States in 2000, is a competent vector of severalPotyviridae. Soybean aphid has high fecundity and produces alatae (winged morphs) readily, characteristics typical of proficient virus vectors. When soybean aphids were exposed toPotato virus Y (PVY)-infected potato plants and then clip-caged on healthy potato plants in groups of five or as single aphids, PVY transmission ranged from 14% to 75% across all experiments. PVY^o, PVYⁿ, and PVP^ntn strains were transmitted by soybean aphid.     

Mineral Oil Inhibits Movement of Potato Virus Y in Potato Plants in an Age-Dependent Manner

Potato Virus Y (PVY) is one of the most devastating pathogens threatening potato production worldwide. It is a RNA virus that is disseminated by aphids in a non-persistent manner. Regular application of mineral oil on potato fields is known to reduce the number of PVY-positive tubers in post-harvest testing. The mechanism of this phenomenon is not well understood, but it is hypothesized to influence the virus-vector-plant relationships. Here, we present data from greenhouse and field trials that shed light on the effect of mineral oil on local and systemic accumulation of PVY^O in susceptible Shepody and Russet Burbank. The data suggests that mineral oil did not influence PVY^O levels in mechanically-inoculated leaves nor tubers of plants with a secondary infection. However, a reduction in systemic PVY^O levels was observed in mineral oil-treated older plants but not in younger plants, suggesting that mineral oil inhibits PVY^O movement in an age-dependent manner.     

Comparison of Straw Mulch,Insecticides, Mineral Oil,and Birch Extract for Control of Transmission of Potato virus Y in Seed Potato Crops

Potato virus Y (PVY) is a major pathogen of potato and transmitted non-persistently by aphids. Aphis fabae is the main vector of PVY in the High Grade Seed Potato Production Area (HG area) in Finland, where the number of aphids and infection pressure with PVY are rather low, but problems with PVY occur in PVY-susceptible cultivars. The aim of the study was to test straw mulch, mineral oil, birch extract, and insecticides for control of PVY in small-scale field experiments and, additionally, at farm level in growers’ fields in the HG area of Finland. The insecticide esfenvalerate reduced the incidence of PVY in the progeny tubers by 29% in one of the 3 years, whereas other chemical treatments or birch extract had no significant effect on PVY incidence. Spraying foliage with mineral oil (Sunoco 11 E/3) reduced the incidence of PVY in 2 years by 43 to 58%, respectively. Straw mulch spread to the field at the time of plant emergence reduced PVY incidence in all 3 years by 50–70%. At farm level, straw mulch reduced the incidence of PVY in the progeny tubers by 25–47%, respectively, in both years tested; however, combining application of straw mulch and mineral oil did not further reduce incidence of PVY. Successful control of PVY in the HG area of Finland using straw mulch may be explained by transmission of PVY early in the growing season at the time of plant emergence and the relatively low number of vector aphids.     

Myzus persicae (Sulzer) in diffuse light and dark rustic storages and resultant PLRV transmission

Population levels ofMyzus persicae (Sulzer) were studied on potato tubers in diffuse light and dark rustic storage houses in Peru. No differences in numbers of aphids/sprouted eye on potatoes infested naturally during storage in diffuse light or darkness were observed. Significantly more alate aphids were observed on tubers stored in darkness than in diffuse light storage houses. Viral transmission was occurring during the storage period. The incidence of viral transmission was not significantly influenced by storing tubers in diffuse light or dark storages. There were significantly more plants infected with virus from tubers that had not been sprayed for aphid control than from tubers that had been sprayed     

Effect of repeated applications of insecticides to potatoes on numbers of Myzus persicae (Sulzer) (Hemiptera: Aphididae) and on the frequencies of insecticide-resistant variants

Numbers of Myzus persicae on potatoes (Solanum tuberosum) receiving three insecticide regimes were recorded in 1985 and 1986. Frequencies of insecticide-resistant variants were determined using an immunoassay for esterase-4 (E4), the enzyme responsible. M. persicae was more abundant at the end of the season on plots sprayed alternately throughout the experiment with a mixture of pyrethroid with oil and pirimicarb, than on those treated with pirimicarb alone. Frequency distributions of E4 activity showed that very resistant variants intermediate between R₂ and R₃ levels accounted for >50% of the populations. Further samples of aphids, collected on separate farms from defoliated patches in late-growing potato crops where repeated spraying had failed to control aphids, showed that these highly resistant variants had again been selected. Possible reasons for the observed increase in numbers of M. persicae following pyrethroid/oil treatment and consequences for virus control are discussed.     

Acquisition of potato leafroll virus byMyzus persicae from secondarily-infected potato plants of different genotypes

Summary The acquisition of potato leafroll virus (PLRV) byMyzus persicae nymphs from the top leaves of potato plants was studied throughout a growing season in relation to the antigen titre in those leaves and the feeding behaviour of the aphid. Secondarily-infected plants of eight potato genotypes with different levels of field resistance served as virus sources. Early in the growing season, plants were efficient sources for virus acquisition. The amount of viral antigen detected inM. persicae nymphs fed on the top leaves was strongly correlated with the titres of viral antigen in these leaves. Virus acquisition from the top leaves of older potato plants was markedly impaired and could not be correlated with their virus titre. With increasing age of the potato plants and the development of virus symptoms, the virus titre in the leaves declined and the initial weak correlation between the virus titre and field resistance ratings disappeared. Thus, screening secondarily-infected potato plants for field resistance to PLRV based on the concentration of viral antigen in leaves or in aphids fed on them should be avoided later in the growing season. The feeding rate ofM. persicae, measured by the number of honeydew droplets excreted, did not account for the reduced uptake of virus from older plants since it was not influenced by the age of the plant. Throughout the growing season, the feeding rate ofM. persicae nymphs on PLRV-infected plants was higher on genotypes with low levels of field resistance to PLRV than on genotypes with high ones.     

Transmission of potato leaf roll virus byMyzus persicae (Sulz.) from leaves and plants of different ages

Summary Young potato plants were a better source of potato leaf roll virus (PLRV) for aphids,Myzus persicae (Sulz.), than old ones. For plants 6, 7.5 and 9 weeks old, the best sources of PLRV were the lower, middle and upper leaves, respectively. The frequency of PLRV transmission from upper leaves did not change much with increasing age of plants nor did it change with different leaflets from the same leaf.     

Evaluation of mineral oil sprays for reduction of virus Y spread in potatoes

In 1979 and 1980 field tests were made at Fredericton, New Brunswick to evaluate the effect of various oil application methods on the spread of potato virus Y (PVY) and the phytotoxicity they might cause. Control of PVY by oil sprays reached 64%. Control of spread depended largely on the concentration of the oil, and to a lesser extent, on its delivery rate. Tests did not show any significant effect of the spray pressure. There was no significant difference between eight commercial oil formulations. No significant foliar phytotoxicity or yield reduction resulted from applications of oil, except when a combination of high oil concentration (3% water emulsion) and high rate of application (2240 L/ha) was used. Fungicides mixed with oil or applied immediately after oil produced foliar phytotoxicity. Less phytotoxicity occurred when they were applied 24 h later than oil.     

应用RT-PCR技术检测马铃薯A病毒

参考GenBank中马铃薯A病毒(potato virus A,PVA)的保守序列,利用Primer6.0引物设计软件设计并合成了一对特异性引物PVAF、PVAR,以此引物利用RT-PCR方法对PVA保守序列基因进行了特异性扩增。结果表明:引物PVAF、PVAR能从已知的感染PVA病毒的植株中扩增出834bp的cDNA特异性片段;该RT-PCR的检测灵敏度为1pg的病毒核酸,特异性强,重复性好,可用于PVA病毒的快速检测。     

Reevaluation of the potato aphid,Macrosiphum euphorbiae (Thomas), as vector of potato virus Y

The effectiveness of the potato aphid,Macrosiphum euphorbiae (Thomas), to transmit potato virus Y (PVY) to potato has generally been overestimated because tobacco has been used as the indicator host. Our results demonstrate that, although apterousM. euphorbiae can acquire PVY from potato and tobacco plants and transmit it to tobacco plants, it does not readily transmit it to potato plants. Alatae only transmitted the virus to 4.5% of potato plants. This relative inability to transmit the virus to potato seems independent of potato cultivar. Results suggest that the role of the potato aphid in the spread of PVY in potatoes may be negligible.     

PSTV与PVY的互作及其对马铃薯产量影响

本文分别在温室和田间条件下利用人工接种的方法研究了马铃薯纺锤块茎类病毒（ＰＳＴＶ）和ＰＶＹ在克新４号及Ｋｅｎｎｅｂｅｃ两品种上的相互作用．试验结果表明：在温室条件下ＰＳＴＶ和ＰＶＹ的复合接种均能在二品种上不同程度地产生条型坏死症状，而在田间未出现明显症状．ＰＳＴＶ与ＰＶＹ混合接种或ＰＳＴＶ接种一周后再接ＰＶＹ会促进ＰＶＹ增殖，植株内ＰＶＹ的浓度显著高于单独接种ＰＶＹ，但ＰＶＹ侵染后再接ＰＳＴＶ对ＰＶＹ的浓度无显著影响．ＰＳＴＶ和ＰＶＹ的工作对ＰＳＴＶ的浓度无显著影响．ＰＳＴＶ与ＰＶＹ复合侵染的三个接种类型都明显地降低平均单株产量和商品薯率，产量损失最大的处理为ＰＳＴＶ与ＰＶＹ混合接种，可导致克新４号减产４５．４％。     

Solanum demissum P.I. 230579, a True seed diagnostic host for potato virus Y

Seedlings ofSolarium demissum P.I. 230579 in the 5-to 10-leaf stage growing under 18-hour days and at 20 to 24°C developed dark, irregular, slightly elongated local lesions 3 to 5 days following inoculation with any one of three strains of potato virus Y (PVY). Local lesions did not develop after similar inoculations with any one of two or more strains each of potato viruses A, M, S, X, or spindle tuber and a single strain each of potato calico and potato yellow dwarf. Inoculations from diseased specimens infected with PVY plus potato viruses A, M, S, and X, singly or in some combinations did not affect the efficiency of P.I. 230579 in detecting PVY in the mixed infections. Plants of P.I. 230579 developed significant numbers of local lesions from PVY inoculations at temperatures from 16 to 27°C and at inoculum dilutions through 1:100. Excised individual leaves of P.I. 230579 can be used to detect PVY. Leaves of plants exposed to air pollutants are unsuitable for assay purposes.S. demissum P.I. 230579 is homozygous for the local reaction to isolates of PVY and is a valuable aid for indexing aphid or mechanically inoculated potato clones or seedlings for resistance to the virus. It is a superior diagnostic host for differentiating PVY from other viruses commonly found in potatoes in the United States.     

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.     

Potato virus A lesions onPhysalis species

PVA produces distinct local lesions on open leaves ofPhysalis floridana, as does PVY. But, whereas PVA induced such lesions on detached leaves, PVY did not. PVX induced similar lesions, thus the test for PVA will be most useful in work with isolated cultures of PVA or with virus tested seed lines or in screening for resistance, where PVX is absent.P. floridana plants and leaves were best held at 15 to 18 C with low light intensity (4–5 K lux). From 4–6 week old potato plants, PVA was best obtained from lower leaves, ground in 0.05 M glycine — 0.03 M phosphate buffer, pH 9.2. One leaf disc infected with PVA could be detected in a composite sample with 9 discs from healthy leaves.P. angulata andP. pubescens may also be used for diagnosis of PVA. PVY becomes systemic in these species without inducing local lesions.     

Advantages of a soluble dye in blot immunobinding assays for virus detection in potatoes

Summary A technique is described in which plant sap is blotted onto small pieces (8×11 mm) of nylon membrane and virus particles bound to the paper are detected by a modification of the enzymelinked immunosorbent assay (ELISA). The detectable product of the assay is a soluble yellow dye, the absorbance of which increased with the virus content of the plant sap. Leaf or tuber sap from plants secondarily-infected with either potato leafroll virus or potato virus Y could be clearly distinguished from that of healthy plants and a majority of tubers primarily infected with PVY were also detected.