Comparison of three potato leafroll virus antisera and a single Beet western yellows virus antiserum for luteovirus detection in potato

Three potato leafroll virus (PLRV) antisera, representing European, British Columbian, and Californian isolates, performed similarly in detection of PLRV in ELISA tests of samples collected in three successive years at the Florida certification test plots and in tests of other samples collected in New York State. Although a range of absorbance values occurred, this was probably due to random variation in virus titers of samples rather than the occurrence of different virus strains or differential serological reactions by the antisera. Beet western yellows virus (BWYV) was detected in potato leafroll samples from nine states and provinces in North America. The BWYV-positive samples represented 40% in 1983 and 62.5% in 1984 of the total number of samples tested. These results confirm previous reports on the widespread occurrence of BWYV in potato with symptoms of leafroll.     

Mainestay: A high-yielding, round white potato variety for fresh market

The Mainestay potato variety is high-yielding and late-maturing producing attractive, round, white-skinned, white-fleshed tubers with medium-shallow eyes. Its major use is expected to be as a maincrop tablestock variety. Mainestay appearance ratings are similar to those of Katahdin, and greening in Mainestay tubers is less than in Kennebec. Most boil and bake qualities were rated equal to Katahdin in at least half of the tests, and Mainestay usually has a low incidence of internal defects. However, purple streak, heat necrosis, vascular discoloration, and heat sprouts have been seen on occasion. Mainestay tubers do not show the net necrosis caused by potato leafroll virus, and have shown very little hollow heart or blackspot bruising. Mainestay is susceptible to common scab and acid scab, but moderately resistant to verticillium wilt (Verticillium, albo-atrum andV. dahliae), early blight (Alternaria solani), rhizoctonia (Rhizoctonia solani), dry rot (Fusarium sambucinum), and pink rot (Phytophthora erythroseptica). It is moderately susceptible to the common race of late blight (Phytophthora infestans). Mainestay tubers are slow to mature after vine kill, and additional time is required prior to harvest in order to allow for proper periderm development and to reduce storage losses.     

Prestile: A new round white potato variety

Prestile is a late maturing potato variety with attractive, round to oblong, white-skinned, white-fleshed tubers with shallow eyes. Its major use is expected to be for tablestock in areas where Katahdin and Ontario are now grown. Prestile tubers are slow to sprout in storage and do not show the net necrosis caused by potato leafroll virus, but are quite susceptible to heat necrosis. This variety is immune to potato virus X, and is moderately resistant to common scab (Streptomyces scabies), verticillium wilt (Verticillium albo-atrum), and early blight (Alternaria solani). Prestile is susceptible to skinning and shatter bruise, and is difficult to kill, particularly when heavily fertilized.     

Quaggy Joe: A high-yielding, round, white potato variety for fresh market

The Quaggy Joe potato variety is high-yielding and medium to medium-late maturing with attractive, round-oval, white-skinned, white-fleshed tubers with medium-shallow pink eyes. Its major use is expected to be as a maincrop tablestock variety. Quaggy Joe is resistant to the potato leafroll virus, and is also moderately resistant to early blight (Alternaria solani), dry rot (Fusarium sambucinum), and soft rot (Erwinia carotovora subsp.carotovora). Quaggy Joe tubers have shown very little shatter or blackspot bruising, but sprout earlier than Atlantic. Young plants have shown sensitivity to the herbicide metribuzin.     

Effect of fertilizer,fumigants, and fungicides on leafroll-net necrosis in Russet Burbank potatoes

A total of 112 combinations of 13 fumigants, fertilizers, and a fungicide was tested in replicated plots in eastern Washington in 1963 and 1964 to determine their effects on the net necrosis produced in Russet Burbank potatoes by the leafroll virus. Plots treated with Telone^® (dichloropropenes) or Telone+chloropicrin had significantly fewer tubers discolored with leafroll net necrosis than untreated plots; plots treated with lower rates of various chlorinated propenes and propanes or ethylene dibromide had fewer discolored tubers than plots treated with higher rates of these chemicals; and plots treated with higher rates of various combinations of dichloropropenes with methyl isothiocyanate or 3-bromo-1-propyne had fewer discolored tubers than plots treated with lower rates of these chemicals. An interaction took place between the chemicals and the leafroll virus that either increased or decreased the amount of net necrosis in the tubers. Other types of internal discoloration (OID) in the tubers were significantly increased by Telone treatments in some tests. Telone treatments showed no effects on OID in other tests compared to untreated tubers. Also, nitrogen, at 100 lb/acre and over, significantly increased the other types of discoloration over no nitrogen, but potassium at 0 to 150 lb/acre and pentachloronitrobenzene (PCNB) at 0 to 30 gal/acre showed no significant effect.     

St. Johns: A round white potato variety for fresh market

The St. Johns potato variety is high-yielding and late-maturing with attractive, round to oblong, white-skinned, white-fleshed tubers with mediumshallow eyes. Its major use is expected to be as a maincrop tablestock variety. Taste panels rated St. Johns better than or equal to Katahdin in texture, color, mealiness, and flavor. St. Johns tubers do not show the net necrosis caused by potato leafroll virus, and are resistant to golden nematode, corky ringspot, hollow heart, and blackspot bruising. St. Johns is also moderately resistant to greening, shatter bruise, verticillium wilt, early blight, common scab, the common race of late blight, leafroll,Fusarium sambucinum (dry rot) andErwinia carotovora (soft rot), although some breakdown has been reported in commercial storages. Symptoms of leafroll virus infection are somewhat difficult to detect.     

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.     

Potato leafroll virus purification and antiserum preparation for enzyme-linked immunosorbent assays

Potato leafroll virus (PLRV) was purified from potato foliage and stems with an average yield of 0.14 mg of PLRV/kg of potato. Modifications of an existing purification procedure are reported. Five low dosage (38-118 μg of PLRV) intravenous injections were used to produce a PLRV antiserum for use in enzyme-linked immunosorbent assays (ELISA) from tubers. PLRV was readily detected in ELISA testing of potato tubers and leaves and inPhysalis floridana Rybd. Non-specific reactions were low with all tissues. In parallel tests, a Canadian antiserum produced higher nonspecific reactions with tuber and leaf tissue. The results indicated that the use of low dosage-intravenous injections might be necessary methodology for producing PLRV antiserum for use in ELISA diagnostic tests with tuber tissue where high non-specific reactions have been reported.     

Effect of applied fertilizer on Kennebec potato top desiccation and yield with diquat

Experiments conducted at Charlottetown, Prince Edward Island (P.E.I.) during 1979–1982 on potato (Solanum tuberosum L. cv. ‘Kennebec’) demonstrated that excessive levels of applied nitrogen made leaf and stem desiccation with diquat (6,7-dihydrodipyrido [1,2- :2′ ,1′-C] pyrazinediium ion) more difficult. A split application of diquat (0.42 kg ai/ha 5 days apart) improved leaf and stem desiccation by as much as 21 and 27% respectively compared to a single application at 0.84 kg ai/ha. Diquat treatments had no effect on vascular discoloration. The high levels of applied nitrogen increased the yield of tubers greater than 60 mm in diameter but reduced the yield of seed size tubers in the 40 to 60 mm size range.     

A two-step ELISA for rapid,reliable detection of potato viruses

The reliability of the standard double antibody sandwich enzymelinked immunosorbent assay (DAS-ELISA) was compared with a shorter, two-step DAS procedure in which sample and conjugate were mixed and incubated together in one step. The two assays were compared using beet western yellows virus and potato leafroll, M, S, X, and Y viruses. The two-step procedure was more sensitive,i.e., it detected small quantities of virus with greater statistical reliability than the standard procedure. At high virus concentrations, the standard produced stronger ELISA reactions than the two-step assay, but both assays were reliable. Since all of the viruses tested withstood high incubation temperatures, the incubation period for the two-step procedure could be reduced to 1 hr at 30 or 37 C. Therefore, assays could be completed within 2 hr using the two-step procedure compared with 2 days for the standard procedure. Reliable results were achieved with samples prepared by grinding tissues in buffer or, more simply, by adding pure, pressure extracted juice directly to conjugate in assay wells. Coating plates with gamma globulins or with F(ab′)₂ fragments of gamma globulins gave equally reliable results with all viruses except potato leafroll, where coating with gamma globulins was superior.     

Evaluation of procedures for detection of pectolyticErwinia spp. on potato tubers

The effectiveness of a tuber incubation method for detection ofErwinia carotovora var.atroseptica andE. carotovora var.carotovora in potato tubers was compared with a lenticel sampling procedure. In the first method, tubers were injured by puncturing lenticels with sterile toothpicks, then wrapped in moist paper towels and polyvinylidene film, and placed in closed chambers flushed with N₂. In later experiments, wrapping tubers in two layers of polyvinylidene film and incubation in air was found to be as effective as the single layer of polyvinylidene and incubation in chambers flushed with N₂. Isolations were made on a selective crystal violet pectate (CVP) medium from homogenized samples of tissue removed from soft rot lesions developing around injured lenticels. In the second method, 10 lenticels/tuber were aseptically removed with a scalpel and homogenized in distilled water; the suspension was plated on CVP. The first method was less tedious and slightly more effective than the lenticel sampling method. In a preliminary survey, these methods were used to detectErwinia infestations in small samples of certified seed potato tubers from Maine, Minnesota, Montana, New York, North Dakota, and Wisconsin. PectolyticErwinia spp. were detected in at least one sample from each state except Montana. The percentage of tubers withErwinia infestations varied from 0–100% among samples. Characterization ofErwinia isolates showed that bothE. carotovora var.carotovora andE. carotovora var.atroseptica were present. PectolyticErwinia spp. on symptomless potato seed tubers may serve as inoculum sources for blackleg and soft rot diseases.     

Serogroups ofErwinia carotovora involved in systemic infection of potato plants and infestation of progeny tubers

Enrichment techniques and serological strain typing methods were used to determine the source of stem and progeny tuber populations ofErwinia carotovora (Ec) in 1980 and 1981. Plots were established in a field that had been planted with potatoes since 1972. Seed tubers of cultivars Russet Burbank and Norgold Russet were assayed forErwinia carotovora pv.carotovora (Ecc) andErwinia carotovora pv.atroseptica (Eca) by tuber peeling and direct plating and plating following enrichment in a pectate-based broth. Levels of seed tuber infestation ranged from undetectable to 2.4 × 10⁴ colony-forming units per g peel tissue. Prior to planting Ecc was detected in soil samples from field plots by enrichment in a pectate-based broth. Ec was isolated from symptomless plants with increasing frequencies from 8 weeks following planting regardless of the level of Ec populations in seed tubers. At harvest progeny tuber recontamination was low and not related to levels of seed tuber Ec populations. In 1980, serological typing of representative Ecc isolates indicated serogroups III, XXIX, and unknown strains isolated from the soil but not the seed tubers prior to planting were isolated from stems and progeny tubers. Serogroup XXIX was isolated from soil, seed, stems and progeny tubers in 1981. Throughout both years, Ecc was isolated more frequently than Eca from seed, soil, stems, and progeny tubers. These data emphasize the potential for reinfestation of seed stocks and infection of plants by populations of Ecc that overwinter in soil under Wisconsin conditions.     

Stage of development of leaf and tuber tissue of the potato plant influences the titer of potato virus M

The enzyme-linked immunosorbent assay (ELISA) was adapted for the detection of potato virus M (PVM). Detectability of PVM was influenced by the stage of plant growth and that of the plant part assayed. In young potato plants, one week prior to flowering, PVM titer was relatively high (0.77 A_405nm units) in the basal leaves and barely detectable (0.09 A_{405 nm} units) in the top leaves. In mature plants, two weeks prior to harvesting, top leaves contained more virus (0.34 A_{405 nm} units) than middle (0.24 A_405nm units) or basal leaves (0.15 A_{405 nm} units). In rapidly growing tubers PVM content was higher (1.57 A_{405 nm} units) than that in fully grown tubers (0.71 A_405nm units) whereas the virus was not detectable in the mother tuber four weeks following planting. PVM was reliably detected when disks from intact leaves were substituted for leaf extracts as the test sample     

Survival ofErwinia carotovora in Wisconsin soils

Erwinia carotovora var.atroseptica (van Hall) Dye andE. carotovora var.carotovora (Jones) Dye were detected in agricultural soils in Wisconsin using baiting and enrichment techniques. These soft rot bacteria could not be detected in soils of potato fields prior to planting of crops in the spring period using standard soil dilution plating techniques on a crystal violet pectate medium, however. A procedure involving incubation of samples in pectate enrichment broth followed by preparation of smears on slides and treatment with a fluorescent antibody stain specific forE. carotovora var.atroseptica was the most sensitive of the methods tested for detecting the blackleg pathogen. Erwinia carotovora was isolated more frequently during the spring from fields in which potatoes had been grown the previous year than from fields in which other crops had been grown. It was also isolated from potato tubers and stems that had overwintered in the field. The presence ofE. carotovora could not be detected in root zone samples of weed plants using the dilution plating method.     

Use of enzyme-linked immunosorbent assay to detect potato leafroll virus in field grown potato,cv. Russet Burbank

Use of enzyme-linked immunosorbent assay (ELISA) in detecting potato leafroll infections in field grown potato, cv. Russet Burbank, was studied from 1986 to 1988 at Rosemount, Minnesota. The objective was to determine relative reliability of current season foliage ELISA, tuber tissue ELISA, and tuber progeny foliage ELISA. Serological tests were most accurate when foliage of tuber progenies was tested. ELISA underestimated total leafroll infection when current season foliage from the inoculated plant was used, in those plants inoculated during late tuber bulking stage. Current season foliage ELISA tests using newly expanded terminal leaflets were more reliable than were tests using older leaflets. Leafroll infection was detected in the current season foliage and tuber progenies (tuber tissue as well as tuber progeny foliage) of some plants seven days after inoculation. Most current season foliage infections were detected by day 14–28 depending on year. Differences among years were most likely caused by variation in quality of virus source plants and numbers of vectors used in inoculation. ELISA tests on tuber tissue were almost as effective as ELISA tests on tuber progeny foliage in detecting potato leafroll 20 days after inoculation, but ELISA on tuber tissue substantially underestimated infection if plants were sampled earlier. Maximum percent tuber infection occurred 20 days or more after inoculation. Movement of the virus from the inoculated stem to other stems decreased with increased plant age at inoculation. Percent infected tubers declined with increased plant age at inoculation. Action thresholds developed for aphids in managing potato leafroll virus should take into account the temporal change in percent infected tubers.     

Fungi associated with Collembola and mites isolated from scabby potatoes

Collembola and mites from the lesions of tubers infected with the acid scab organism were tested for the presence of fungal potato pathogens.Streptomyces spp. were found on and in the bodies of these arthropods.Verticillium albo-atrum was present on the external surface and in the body of the Collembola. Various other soil-inhabiting fungi which are not known to be potato pathogens and which were found on and in the bodies of these arthropods are noted.     

Factors affecting the accuracy of the tuber incubation test for the detection of contamination of potato stocks byErwinia carotovora

Summary Erwinia carotovora in potato stocks can be detected more efficiently by the tuber incubation method in which the test tubers are first induced to rot under anaerobic conditions (followed by detection isolation of the bacteria on a selective growth medium or by serological techniques) than by direct lenticel sampling. However, the efficiency of detection is affected by both the extent of decay at sampling time and the incubation temperature. Detection ofE. carotovora is poor from extensive lesions developed at temperature of 25 C or above. Furthermore, detection ofE. carotovora var.atroseptica is more frequent than that ofE. carotovora var.carotovora at temperatures below 22 C in tubers contaminated by both organisms, whereas at higher temperatures the reverse is true. Only within a narrow temperature range, close to 22 C is there an equal chance of detecting both varieties.     

Portage: A new early-maturing,round white table potato variety

The Portage potato variety is high-yielding and early-maturing with attractive, round to oblong, white-skinned, white-fleshed tubers with medium-shallow eyes. Its major use is expected to be as an early tablestock variety in areas where Superior suffers yield reductions caused by verticillium wilt. Portage tubers do not show the net necrosis caused by potato leafroll virus, and are susceptible to skinning, but are fairly resistant to hollow heart, blackspot and shatter bruise. Portage is moderately resistant toVerticillium alboatrum, andRhizoctonia solani, but its seed-pieces are sensitive to dry soil conditions; therefore, cut seed should be suberized before planting. Symptoms of leafroll virus infection are difficult to recognize.     

Hypoxic stress inhibits aerobic wound-induced resistance and activates hypoxic resistance to bacterial soft rot

Resistance to bacterial soft rot in potato tubers maintained aerobically was induced by wounding tubers 4 to 24 h prior to inoculation withErwinia carotovora subsp.carotovora. This wound-induced resistance phenomenon was blocked by hypoxic stress. An hypoxia-induced resistance mechanism also was detected: tubers acclimated to a hypoxic environment were resistant to rot when inoculated with aerobically grownE. c. subsp.carotovora and incubated in atmospheres made hypoxic by argon or nitrogen. With increased pretreatment, hypoxia-induced resistance approached the levels of resistance observed in tubers inoculated with aerobic-adapted bacteria and incubated aerobically. Hypoxia-adaptedE. c. subsp.carotovora overcame hypoxia-induced resistance.     

Effect of chemicals on vine kill,yield and quality of potatoes in the Red River Valley

Sodium arsenite at 9 lb, DNBP at 2.5 lb, diquat at 1 lb, paraquat at 0.5 and 1 lb and prep at 2 and 4 lb/acre were tested as vine killers for potatoes during 1963, 1964 and 1965. Based on ratings 1 or 2 days after spraying, 1 lb diquat, 1 lb paraquat and 2.5 lb/acre DNBP resulted in the quickest kill. Paraquat at 0.5 lb and sodium arsenite at 9 lb/acre were slightly slower. Prep at 2 and 4 lb/acre was consistently slowest. Some of the slower acting chemical gave equally good kill after 7 days. Chemical vine killing usually reduced yields and specific gravity by shortening the growing period. There was no effect from any of the chemicals on the color of potato chips. A slight amount of vascular discoloration did occur in tubers from all treatments. Vascular discoloration of tubers from vines treated with prep at 2 lb/acre was greater than that of tubers from vines which were cut and not sprayed. None of the vascular discoloration was severe enough to be economically important. In a second test sodium arsenite at 9 lb and diquat at 0.5, 1 and 2 lb/acre were applied as single and split applications in 1963. The major effect from the split applications was a slower rate of vine kill.