Diploid genotype DW.84-1457, highly resistant to potato leafroll virus (PLRV)

Summary The diploid clone DW.84-1457 which has outstanding resistance to potato leafroll virus (PLRV), has been selected at the Mlochów Centre of the Institute for Potato Research. It has in its pedigree PLRV-resistant clones from the Max Planck Institute nos. MPI 44.1016/10, MPI 44.335/130 and MPI 49.540/2. Its behaviour in the field and response to aphid inoculation indicate high resistance to infection, and the low concentration of the virus in graft-inoculated plants indicates high resistance to multiplication. This combination within one genotype of two aspects of resistance is not connected with hypersensitivity, and is heritable. Clone DW.84-1457 has other desirable characters such as extreme resistance to potato virus X (PVX), high resistance to potato virus M (PVM) and good table and processing quality. It is being utilized in the development of parental lines, both at the diploid and tetraploid level.     

Resistance of potato clones to the green peach aphid and potato leafroll virus

During 1980 and 1981 potato cultivars and breeding selections, including cultivated species and their hybrid derivatives, were evaluated for resistance to the green peach aphid (GPA),Myzus persicae (Sulzer), and to potato leafroll virus (PLRV). Criteria used were the number of aphids which colonized the clones in free choice field experiments and the number of plants derived from these experiments which showed symptoms of PLRV infection. Generally, greater resistance to GPA was found inSolarium tuberosum gp.andigena selections and hybrids than in gp.tuberosum cultivars. There were approximately fourfold differences in season-mean GPA levels among the clones tested each year. Forty-two families, representing a cross-section of the USDA breeding populations at the University of Idaho Research and Extension Center, Aberdeen, showed a similar range in colonization levels. Resistance to GPA colonization appeared to be more prevalent in gp.andigena, gp.phureja, and gp.stenotonum derivatives. There was a weak positive correlation (r² = .34, P = .01) between foliar total glycoalkaloids and season-mean GPA colonization levels for six clones representing the range of observed resistance to GPA. Resistance to GPA colonization was apparently not directly related to resistance to PLRV infection. Katahdin, for example, was relatively susceptible to GPA colonization but very resistant to PLRV infection whereas selection A69657-4 (gp.andigena) was among the most resistant to GPA colonization but among the more susceptible to PLRV infection. Breeding for resistance to GPA colonization therefore may not be as promising for PLRV control as developing PLRV resistant cultivars.     

Progeny tests to identify diploid potato clones homozygous at loci controlling resistance to PLRV

Summary Using potato parental lines homozygous at a locus or loci controlling resistance to potato leafroll virus (PLRV) can give advantages in the selection of resistant forms. In order to identify homozygous diploid clones their test-cross families were evaluated. All the clones that were test-crossed expressed resistance in primarily- and secondarily-infected plants and etiolated sprouts, and were derived from mating genotypes highly resistant to PLRV. Genotypes from test-cross families varied in resistance to PLRV, and one family was found which had only resistant genotypes, suggesting that the resistant parent of this progeny was homozygous at resistance loci. Evidence was gathered that resistance in some diploid clones may result from resistance to virus multiplication as well as restricted virus transport from leaves to tubers.     

Host genes and transgenes that confer resistance to a Scottish isolate of potato leafroll virus are also effective against a Peruvian isolate

Summary Potato genotypes with host gene-mediated resistance (host-MR) and coat protein-mediated transgenic resistance (CP-MR) to potato leafroll virus (PLRV), were inoculated with a Scottish and a Peruvian isolate of PLRV. The coat protein transgene had been cloned from the Scottish PLRV isolate which had also been used during the screening and selection of genotypes with host resistance. Significantly less PLRV accumulated in plants with either host-MR or CP-MR than in plants of susceptible genotypes or in non-transformed control plants, but the two forms of resistance were equally effective against both PLRV isolates.     

Biological factors influencing the transmission of potato leafroll virus by different aphid species

Summary Macrosiphum euphorbiae, collected in the field from potato plants infected with potato leafroll virus (PLRV), transmitted the virus to fewer potato plants in a field trial than did laboratory-rearedMyzus persicae. In the laboratory,M. persicae was the only efficient vector of PLRV fromPhysalis floridana seedlings, potato sprouts or excised leaves toP. floridana. Two clones ofM. euphorbiae and one clone ofAulacorthum solani transmitted PLRV from infected potato plants toNicotiana clevelandii as effeciently asM. persicae but a clone ofAphis gossypii was an inefficient PLRV vector. An isolate of PLRV, whichM. persicae transmitted inefficiently from potato toN. clevelandii, was also transmitted inefficiently byM. euphorbiae andA. solani.     

Potato leafroll virus spread in differentially resistant potato cultivars under varying aphid densities

An action threshold of 3-10 green peach aphid,Myzus persicae (Sulzer), apterae per 100 lower leaves is recommended for use in Minnesota to prevent further spread of potato leafroll virus (PLRV) in potato,Solarium tuberosum L. This threshold was first developed and validated using the PLRV susceptible cultivar Russet Burbank. Here we report experiments to determine if higher aphid densities could be tolerated in PLRV resistant cultivars,i.e., Kennebec (moderately resistant) or Cascade (highly resistant), without an increase in PLRV infection. Insecticidal sprays were applied to plots when predetermined target aphid densities, based on number of apterae per 100 leaves, were reached: 3, 10, 30, and 100 (Russet Burbank); 10, 30, 100, and 300 (Kennebec); and 30, 100, 300, and 1000 (Cascade). The response variable was the average percentage of PLRV infected plants. Overall mean cumulative aphid-days and percent PLRV infection were 617 and 23.5% for Russet Burbank, 1,296 and 10.2% for Kennebec, and 4,816 and 9.5% for Cascade. For each cultivar, the highest target aphid density tolerated without an increase in PLRV spread was determined by comparing PLRV infection in plots sprayed on predetermined thresholds to PLRV infection in plots where aphids were rigorously controlled. This maximum density was 10 apterae per 100 leaves for Russet Burbank and 300 apterae per 100 leaves for Cascade. Results using Kennebec were ambiguous, but Kennebec was always more resistant to PLRV than Russet Burbank. Excised leaflet tests showed that the cultivars did not differ in resistance to green peach aphid. It appears that action thresholds based on green peach aphid apterae can be different depending upon the inherent PLRV-resistance of the cultivar.     

General resistance against potato virus Y introduced into a commercial potato cultivar by genetic transformation with PVYN coat protein gene

Summary Transgenic cv. Folva potato plants expressing the coat protein gene of potato virus Y strain N (PVY^N) were produced usingAgrobacterium tumefaciens mediated transformation. Forty independent transformants were selected for resistance screening. Four clones showed complete resistance to mechanical inoculation with all the five PVY isolates tested: the PVY^N isolate from which the coat protein gene was derived, two PVY^O isolates, and two PVY^NTN isolates. Two of the fully resistant clones contained only one copy of the transgene, demonstrating that it is possible by genetic engineering to obtain highly virus resistant potato clones that can also be useful in future breeding programmes.     

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.     

Enzymatic discoloration and phenolic content of potato tubers from cultivars resistant and susceptible to the golden nematode

Phenolic content and discoloration were determined for 13 commercial potato cultivars and 6 potato clones grown at 2 locations over a period of 5 successive years. Tubers from 6 potato cultivars and 5 potato clones resistant to the golden nematode were compared with tubers from 7 potato cultivars and 1 clone known to be susceptible to the golden nematode. Tubers from resistant plants were lower in phenols and discolored less than tubers from susceptible plants.     

马铃薯植株感染Y病毒后生理指标变化与抗病性的关系

本研究分别以对PVY感病、过敏和极端抗性的品种脱毒试管苗为材料,比较了接种PVY后不同时间内超氧化物歧化酶(SOD)和游离脯氨酸含量2个指标的变化。从整体上看,未接种PVY条件下,感病品种(Superior)植株的SOD活性较极端抗性品种(IVP35)和过敏型品种(Desiree)低。接种后,IVP35的SOD活性下降;Desiree在接种前期0.5～1 d SOD的活性下降,2～7 d后SOD活性上升,再后7～14 d又下降;Superior接种PVY后,SOD活性有上升趋势,且在接种2～3 d变化率出现最大值。另外,IVP35和Desiree在接种PVY后SOD变化率小,变化范围分别为-13.4%～4.6%和-17.8%～8.7%;Superior接种PVY后,SOD活性变幅较大,范围为5.1%～79.2%。被测的3个品种无论接种与否,极端抗性品种和过敏型品种其植株内部游离脯氨酸含量均明显高于感病品种。正常情况下,IVP35和Desiree的游离脯氨酸含量为41.39～48.77μg.g-1干重和33.42～39.11μg.g-1干重,而Superior仅为8.91～10.72μg.g-1干重。接种PVY后,Superior的游离脯氨酸含量明显上升,达到11.23～21.54μg.g-1干重;虽然IVP35和Desiree的游离脯氨酸含量也呈上升趋势,但上升幅度小,含量分别为48.92～72.13μg.g-1干重和42.46～71.34μg.g-1干重。     

Monitoring current season potato leafroll virus movement with an immunosorbent direct tissue blotting assay

A direct tissue blotting assay (DTBA) was used to track the movement of potato leafroll virus (PLRV) from newly infected foliage to the tubers. Plant and tuber characteristics were recorded to assess plant growth stage at inoculation and PLRV effect on yield. Russet Burbank potatoes were planted at different times in 1991 and 1992 to provide plants of different maturities which were then inoculated using PLRV carrying aphids. Aphids were allowed to feed two to three days after which an insecticide was applied. Stems and tubers were tested periodically for PLRV with DTBA after inoculation. Indexed tubers were grown out and ELISA tested in the greenhouse the following winter to confirm results of summer serological tests. Plant age affected percentages more consistently than did inoculation date. When plants approximately 43 days from planting were inoculated at different dates, early inoculation produced a higher percentage of infected plants. Conversely, when plants approximately 62 days from planting were inoculated at different dates, late inoculation resulted in a higher percentage of infected plants. However, early inoculation of young plants resulted in the highest infection percentages. Tuber size and yield were negatively affected by higher percentages of leafroll regardless of the stage of growth at inoculation. DTBA is best used for detecting PLRV in foliage of plants grown from infected tubers (i.e. secondary PLRV). DTBA is less accurate for detecting primary PLRV.     

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 leafroll virus to or from tuber slices by aphids feeding through a membrane

Summary Eye-bearing slices, cut from healthy potato tubers and placed between Parafilm membranes, were inoculated with potato leafroll virus (PLRV) byMyzus persicae. PLRV was detected by ELISA and by transmission tests in tuber slices and in plants grown from the slices of the susceptible cv. Désirée, but not in those of the resistant cv. Arkula. These results suggest that PLRV replication and transport within tuber phloem is controlled by specific mechanisms of resistance.M. persicae was also able to acquire and transmit PLRV toPl floridana from slices cut from tubers of infected plants. The aphids effectively transmitted PLRV from slices cut from the sprouting rose end but they failed to transmit it from slices cut from the heel end of tubers.     

Reaction to the potato leafroll virus (PLRV) in diploid potatoes

Summary Diploid parents with some resistance to PLRV, were intercrossed to give 3 families with 191 clones which were evaluated for reaction to PLRV and yielding ability. After inoculation with PLRV the clones could be separated into those: 1) resistant, 2) susceptible, 3) intolerant, reacting with low virus concentration, 4) tolerant and 5) intermediate in reaction. Both the ELISA test and the evaluation of external disease symptoms were necessary to separate the clones. No correlation was found between resistance to PLRV and tuber yielding ability.     

Resistance to potato leaf roll virus inSolanum brevidens

Summary Plants ofSolanum brevidens graft-inoculated with potato leaf roll virus (PLRV) grew vigorously and had a normal healthy appearance. Although presence of the virus was confirmed in all inoculated plants by graft tests to potato and/orDatura stramonium, recovery of PLRV fromS. brevidens PI 218228 usingPhysalis floridana and the aphidMyzus persicae was erratic and only few test seedlings became infected. Ease of recovery of the virus using aphids was not influenced by presence of a continuous graft union with infected potato. Testing ofS. brevidens PI 245763 withM. persicae was not possible due to poor aphid survival on plants of this accession.     

Unusually mild symptoms of potato leafroll virus in the progeny of late-infected mother plants

Summary In a field experiment in which the date of potato leafroll virus (PLRV) inoculation was controlled, progeny plants derived from late infection of mother plants in the previous year showed much milder symptoms than progeny plants derived from mother plants that became infected earlier in the season. Plants with these milder symptoms contained as great a concentration of PLRV as progeny plants with more obvious symptoms derived from early primary infections.     

Selection of first-year potato seedlings for resistance to potato leaf roll virus

Summary In families obtained from crossing pairs of parents with high resistance to potato leaf roll virus (PLRV), individual clones differ greatly in their level of resistance. Inoculation of first-year seedlings was effective in selecting more resistant families, but it was not so effective in selecting more resistant individual clones.     

马铃薯病毒外壳蛋白融合基因转化马铃薯及其抗病性分析

将多种病毒的有效核酸片断拼接成融合基因转入马铃薯可获得多抗马铃薯材料。针对马铃薯生产中分布广泛、危害严重并经常混合感染的马铃薯X病毒(PVX)、马铃薯Y病毒(PVY)、马铃薯卷叶病毒(PLRV)和马铃薯S病毒(PVS),开展了利用基因工程方法获得兼抗4种马铃薯病毒转基因马铃薯材料的研究。试验在前期获得含4种马铃薯病毒外壳蛋白基因片段的质粒pART27-XSYV-rh的基础上,通过根癌农杆菌(Agrobacterium tumefaciens)介导转化马铃薯(Solanum tuberosum)品种‘陇薯3号’,PCR扩增和PCR-Southern杂交证明,4价融合基因已整合到马铃薯基因组中。qRT-PCR分析表明,该融合基因在转基因植株中能正常表达。3株转基因植株的抗病性鉴定结果表明,2株对4种病毒同时具有抗性;1株对PLRV侵染表现阳性,对另外3种病毒同时具有抗性。     

Effect of time of inoculation with potato leafroll virus on development of net necrosis and stem-end browning in potato tubers

The Green Mountain cultivar was used in field tests to determine the effects of inoculating potato plants at various times with the potato leafroll virus (PLRV) on development of internal necrosis of tuber tissue. Viruliferous apterae of the green peach aphid,Myzus persicae (Sulz.), were placed on each stem in all hills to be inoculated in each 3.0 m single-row plot. Planting and inoculation dates were varied in all field experiments and, in one, several vine-killing dates were also included. All harvested tubers were stored for approximately four months at 10°C to enhance development of internal necrosis prior to examination. Similar but smaller greenhouse studies involving both apterous and alate green peach aphids were also conducted using Green Mountain, Irish Cobbler, and Russet Burbank cultivars. All results showed that as inoculation was delayed relative to plant development, more net necrosis (NN) occurred. Conversely, when plants were inoculated early, stem-end browning (SEB) rather than NN predominated. A high percentage of naturally occurring SEB tubers (cv. Russet Burbank) were found by ELISA to contain PLRV. Plants produced by these tubers only rarely developed leafroll symptoms. These findings suggest a previously unsuspected causal relationship between SEB and PLRV. Implications of this apparent relationship on the epidemiology of potato leafroll in Maine are discussed.     

Multiplication ofPseudomonas solanacearum in resistant potato plants and the establishment of latent infections

When 1-mo-old plants of a wilt-resistant clone ofSolanum phureja (1386.15) were stem-inoculated with three strains ofPseudomonas solanacearum (K60, S123, and S206), the bacteria multiplied rapidly at the point of inoculation and then moved in the vascular system to other parts of the stem. Resistant plants showed a remarkable ability to support relatively high populations of the bacterium in the absence of disease symptoms. Although multiplication in this resistant clone was substantially less than in susceptible Russet Burbank potato plants, large numbers of bacteria (up to 624 × 10⁴ cells of K60 per 5-cm stem segment) reached the base of the stem of plants maintained at high temperature (28°C) for 20 days after stem inoculation. From the base of the stem, the bacteria moved rapidly into the roots and tubers. Strains ofP. solanacearum differed in their ability to cause latent tuber infection in different resistant potato clones. When 11S.phureja ×S. tuberosum hybrids were stem-inoculated, maintained at 28°C for 3 wk and then grown to maturity at 20°C., most of the clones yielded tubers infected by one or more strains. The race 1 strain (K60) was the most infectious; 53.8% of all tubers harvested from all plants inoculated with this isolate carried latent infections. Because one clone (BR 53.1) never yielded infected tubers, there appear to be genetic factors which may be useful in breeding programs aimed at eliminating latent tuber infection.