The bionomics ofErwinia carotovora in North Dakota

A study into the ecology ofErwinia carotovora in North Dakota was performed to determine possible sources ofErwinia spp. which recontaminate stem cut derived seed stocks (SCDS).Erwinia carotovora pv.carotovora (Ecc) was found to overwinter in naturally infested agricultural soils that had been planted to potato the previous cropping season. However, this bacterium was only present in the 30–71 cm sampling depth.E. carotovora pv.atroseptica (Eca) and Ecc were also found in the rhizospheres of a few weed and crop species but the frequency of recovery was low. Ecc and other strains not identifiable to pathovar, but notE. chrysanthemi, were readily recovered from a variety of water sources and from sunflowers with stem and head soft-rot symptoms. AllErwinia strains were characterized, but not all could be identified to pathovar. WateringErwinia-free potato plants with water naturally infested withErwinia spp. resulted in progeny tubers contaminated withErwinia. The importance of this information with regard to the recontamination of SCDS is discussed.     

Wound-healing and the effect of soil temperature,cultivars and protective chemicals on wound-healed potato seed pieces inoculated with seed piece decay fungi and bacteria

The effect ofFusarium solani (Fsc),F. sambucinum (Fs),Erwinia carotovora subsp.atroseptica (Eca), andE. carotovora subsp.carotovora (Ecc) inoculated singly and in combination (FscFs, FscEca, FscEcc, FsEca, FsEcc, and EcaEcc) on wound-healed potato seed pieces of the cultivar Kennebec was studied. Potato seed pieces wound-healed for 5 days at 13 C and approximately 100% relative humidity, inoculated with Fsc, Fs, Eca, Ecc and their combinations, and incubated for 10 days at 9 C were protected from Eca, Ecc, and EcaEcc. When wound-healed potato seed pieces were inoculated with Fsc, Fs, Eca, Ecc, and their combinations and planted in soil maintained at 7, 10, 15, 20 and 25 C, wound-healing protected seed pieces from all pathogens and their combinations in seed pieces held for 10 days at 10 and 15 C. When seed pieces of cultivars Atlantic, Kennebec, Norchip, Russet Burbank and Superior were inoculated with Fsc, Fs, Eca, Ecc, and their combinations, different levels of protection were observed: Russet Burbank had the highest level of protection, Atlantic and Kennebec were intermediate, and Norchip and Superior were slightly protected. Dusting mancozeb on wound-healed seed pieces before inoculation with Fsc, Fs, Eca, Ecc, and their combinations increased protection against all pathogens and their combinations by 39% or more compared to the nonchemical control.     

Storage of seed potatoes in pallet boxes. 1. The role of tuber surface moisture on the population of Erwinia bacteria

Summary Three stocks of seed potatoes contaminated with soft rot Erwinias were stored for 172 days in a commercial pallet box store. Three treatments were applied: naturally ventilated boxes, forced air ventilated boxes and single tubers on trays. Skin resistance values were 2.3, 9.4 and 19.3 megohm respectively. Rewetting events numbered 4, 7 and 15.Erwinia carotovora pv.carotovora (Ecc) andErwinia carotovora pv.atroseptica (Eca) declined in all stocks and treatments. Ecc declined significantly faster in the forced air ventilated treatment. The more frequent rewettings in the trays reverse the benefit of their drier skins. In the earliest sprouting stock, the naturally ventilated, but not the forced ventilated boxes, showed a decrease in skin resistance and corresponding increase in Ecc as spring approached. Forced ventilation in the first 14 days after harvest halved the level of silver scurf compared to the naturally ventilated treatment.     

Interaction ofErwinia spp. andFusarium roseum ‘Sambucinum’ on the Russet Burbank potato

Laboratory and field studies with the Russet Burbank (RB) potato provide evidence for synergism betweenErwinia carotovora var. atroseptica (Ea) andFusarium roseunt ‘Sambucinum’ (Fs). When these pathogens were inoculated together, the severity of tuber rot was significantly greater than when either pathogen was inoculated separately. Similarly, these pathogens interacted to reduce yield. When both organisms were uniformly applied to puncture wounds on potato seed (inoculum suspension consisted of 10⁸ cells/ml Ea and 10⁵ cells/ml Fs), the total yield was reduced by 46% and U.S. #1 yield by 53%. These reductions occurred even though blackleg symptoms (caused by Ea) were negligible (< 1%). In contrast, inoculations withErwinia carotovora var.carotovora (Ec) and Fs did not interact to reduce potato yield. Potato yields were also not influenced when these pathogens (Ea, Ec, Fs) were separately inoculated.Verticillium wilt (Verticillium dahliae) was significantly less when tubers were inoculated with either Ea, Ec, Fs, Ea + Fs, or Ec + Fs than with uninoculated tubers.     

Evaluation of diploid potato clones for resistance to tuber soft rot induced by strains ofErwinia carotovora subsp.atroseptica,E. carotovora subsp.carotovora andE. chrysanthemi

Summary Tubers of clones from a diploid hybrid population ofSolanum phureja andS. stenotomum were screened for resistance to tuber soft rot caused by strains ofErwinia carotovora subsp.atroseptica (Eca),E. carotovora subsp.carotovora (Ecc) andE. chrysanthemi (Ech). Significant, positive correlations between resistance to the different strains and species were observed, indicating that screening for resistance to tuber soft rot could be accomplished by using just one of the three pathogens. Strains of Ecc and Ech were found to be much more virulent than strains of Eca. Inoculating with Ecc and Ech resulted in more distinct differences among susceptible, moderately resistant and resistant clones than inoculating with Eca.     

Potato early dying disease in the Pacific Northwest caused byErwinia carotovora pv.carotovora andE. carotovora pv.atroseptica

Premature death of potato vines is widespread in irrigated potato fields of the Pacific Northwest.Verticillium dahliae is a major cause of early dying in fields with a history of potato production, but in fields new to potato production, or those that have been fumigated and have a lowV. dahliae population in the soil, premature death of vines can also occur.Erwinia carotovora pv.carotovora (Ecc) andE. carotovora pv.atroseptica (Eca) have been implicated in the early dying disease syndrome in these fields. Both bacterial pathogens are associated with symptoms similar to those caused byV. dahliae; i.e., a progressive chlorosis and necrosis of the foliage and vascular discoloration that may extend a short distance up the stem. Greenhouse pathogenicity studies on cv. Russet Burbank cuttings in which symptom development was identical to that produced byV. dahliae have verified thatEcc andEca can cause potato early dying.     

Evaluation of potato clones for resistance to tuber and stem rot induced byErwinia chrysanthemi

Tubers of 149 clones ofSolarium tuberosum subsp.andigena (andigena) from four self-pollinated (S₁) families (Jak 072, 702440, 700718 and Och 5331) obtained from true seed were rated for resistance toErwinia chrysanthemi. The clones were classified into four arbitrary categories based on disease reaction: resistant, intermediate, susceptible, and very susceptible. In family Jak 072, 23% of the clones were resistant and 61% intermediate. In family Och 5331, 22% of the clones were susceptible and 67% very susceptible; and in families 702440 and 700718, 38% and 29% of the clones were intermediate and 45% and 40% were susceptible, respectively. Tubers of 11 clones chosen to represent each one of the four categories were inoculated withE. chrysanthemi (Ech), E. carotovora subsp.carotovora (Ecc) andE. carotovora subsp.atroseptica (Eca). Clones responded similarly toEch andEca. However,Ecc induced significantly more rot thanEch orEca, presumably favored by the temperature of incubation (25°C). Clones Jak 072-17 and Jak 072-18 were resistant to the three bacterial pathogens. Above ground stems of 6 of the 11 selected clones inoculated withEch were susceptible to stem rot. No correlation was found between the response of tubers and above ground stems to tuber and stem rot induced byEch.     

Identification of stem soft rot (Erwinia carotovora subspeciesatroseptica) resistance in potato

Development of potato cultivars resistant to Erwinia species (Erwinia carotovora subspeciesatroseptica, E. carotovora subspeciescarotovora, andErwinia chrysanthemi) causing soft rot of stems and tubers involves identification and transfer of the resistance to breeding lines possessing desirable agronomic traits. In total, 363 accessions of six wildSolanum species, three somatic hybrids and nine sexual progeny of somatic hybrids were screened for stem soft rot resistance. Thirty-one, 50, and 67 percent of accessions ofSolanum boliviense, Solanum chacoense, and Solanumsanctarosae, respectively, were resistant or highly resistant, whereas, 100, 97, and 95 percent of accessions ofSolanum canasense, Solanum tarijense, andSolanum spegazzinii were susceptible or highly susceptible, respectively. Two tuber soft-rot resistant somatic hybrids, A937 and T355-11 produced earlier by the fusion ofSolanum brevidens (PI 218228) andSolanum tuberosum (PI203900) orS. tuberosum cv. Russet Burbank, respectively, and the sexual progeny of A937 andS. tuberosum cv. Katahdin were also highly resistant. Transfer of resistance fromS. brevidens to somatic hybrid (A937) and subsequently to the progeny suggests that the resistance is simply inherited. In addition to the identification of 65 resistant or highly resistant clones of wildSolanum species, this study has identified three tuber soft rot-resistant clones that are also resistant to stem soft rot. Potato cultivars showed a range of responses to the pathogen.     

Effect of applying nitrogen fertilizer to a potato seed crop on the susceptibility of the daughter plants toErwinia carotovora subsp.atroseptica

Summary Seed potatoes of cvs Record and Bintje were grown with 30, 80 or 130 kg N/ha. In the subsequent growing season the seed tubers, which were inoculated or not with two concentrations ofErwinia carotovora subsp.atroseptica (Eca), were subjected to the same fertilization treatment. The incidence of blackleg and the level of seed tuber decay increased from the uninoculated treatment to the higher inoculum level, but the degree varied considerably from one year to another. Cv. Bintje was more susceptible to blackleg and yield loss caused by Eca than cv. Record. In 1990, when disease incidence was high, the proportion of blackleg stems increased with increasing doses of nitrogen fertilizer which had been applied to the seed crop, but was not significantly affected in 1988 and 1992. Seed tuber decay was retarded by the lowest nitrogen dose. The yield of the subsequent crop was not affected by the nitrogen dose applied to the seed crop.     

Effect of whole seed tuber size and pre-plant storage conditions on yield and tuber size distribution of Russet Burbank

Field experiments were conducted in 1995, 1996, and 1997 at Agriculture and Agri-Food Canada’s Harrington Research Farm to assess the effect of whole seed tuber size and pre-plant seed storage conditions on processing yield (> 51 mm dia.) of potato (Solanum tuberosum L. cv Russet Burbank). Following commercial storage, seed tubers were stored at 4.4 C then subjected to one of three pre-plant treatments: (1) planted directly from storage, (2) held at 10 C for 3 wk before planting, or (3) green-sprouted for 3 wk before planting. Five sizes of whole seed were used (28, 42, 56, 70, and 84 g) with a variable size cut seed treatment added for comparison. Plots were harvested 138,134, and 131 days after planting in 1995, 1996, and 1997, respectively. Cut seed produced a higher yield of tubers > 51 mm diameter in comparison to all whole tuber seed sizes, with the exception of the 28 and 56 g sizes. In terms of total yield, the 28and 42-g whole seed tubers yielded significantly less than all other seed sizes examined. Warming or greensprouting seed tubers prior to planting did not increase tuber yield. The larger whole seed tuber sizes tended to result in greater numbers of stems and tubers per plant. To maximize marketable yield of Russet Burbank planted from whole seed tubers, it is recommended that the seed be between 28 and 42 g in size. Accepted for publication 25 May 2004.     

Inoculation of potato tubers withErwinia carotovora during simulated commercial washing and fluming practices

The potential for bacterial soft rot in potato tubers was affected by laboratory simulation of some components of fluming and washing practices at commercial packinghouses. The potential was expressed as disease severity (average percentage surface decayed) after a standard 4-day incubation at 20°C in a mist chamber. Increased disease resulted when there was an increase in the following factors: a) duration of immersion of tubers in water; b) population of bacteria suspended in water; c) hydrostatic pressure on submerged tubers, and d) concentration of a surfactant (Triton X-100) in the suspensions. A sample of tubers from each tuber lot was uniformly moistened with tap water and then incubated to determine a base-level disease severity. Disease severity in Russet Burbank tubers from commercial storage increased from the base-level of 0.8% to 76% when tubers were immersed in 5 × 10⁶ colony-forming units (cfu)/ml ofErwinia carotovora pv.carotovora (Ecc) for 64 min prior to incubation. Disease severity was 64% when tubers were immersed in a similar suspension for only 0.1 min, but with a hydrostatic pressure of 230 cm of water. Severity values fourto fivefold above control levels (from immersion in water) resulted from an immersion for 5 min in 5 × 10³ cfu/ml with hydrostatic pressures of 5, 180, or 370 cm of water. A 20-fold increase in severity occurred when Red LaSoda tubers were immersed briefly (less than 5 s) in 5 × 10⁶ cfu/ml. Rinsing these tubers with tap water after inoculation, but prior to incubation, did not affect the subsequent development of decay. Thus, the high potential for bacterial soft rot in tubers that have been flumed or washed by water concentrated with soft rotErwinia cannot be reduced by washes or rinses with clean water.     

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.     

The role ofErwinia carotovora in the epidemiology of potato blackleg. II. The effect of soil temperature on disease severity

Relative disease severity (seedpiece decay or post emergence blackleg) incited byErwinia carotovora var.carotovora (Ecc) andErwinia carotovora var.atroseptica (Eca) was studied in the field and the greenhouse. When inoculated tubers were planted in cool soils in the field or greenhouse (7.0–18.5°C average minimum and 16–26°C average maximum temperature during the first 30 days after planting)Eca caused significantly more disease thanEcc. Under these experimental conditionsEcc did not cause significantly more disease than that found in non-inoculated controls. When soil temperatures were high at planting time (21.4–24.0°C average minimum and 29.6–35.0°C average maximum temperature for the first 30 days after planting), inoculation withEcc resulted in severe disease whileEca produced no more infection than that found in uninoculated controls. At intermediate soil temperatures both were infective. Seedpiece decay by both organisms was correlated with soil temperatures during the first 30 days after planting. As the soil temperature increased, inoculation withEcc resulted in more disease than inoculation withEca. At lower soil temperatures the opposite result was obtained. Field and greenhouse studies showed that bothEca andEcc were able to cause typical post emergence blackleg infection, the former at low soil temperature and the latter at high temperature conditions. The data suggest that bothEcc andEca are components of the potato blackleg and soft rot disease complex. Environmental conditions, especially soil temperature, determine which organism is causative under a particular set of conditions.     

Preliminary selection of antagonists ofErwinia carotovora subsp.atroseptica (Van Hall) Dye for application during green crop lifting of seed potato tubers

Summary Green crop lifting (GCL) for haulm killing was developed in The Netherlands and offers ideal conditions for controlling the blackleg pathogenErwinia carotovora subsp.atroseptica (Eca) by antagonists. Based on the use of mini-tubers or young tubers from field crops, two bioassays for wound protection were developed. GCL was simulated by artificially skinning or wounding tubers, inoculating the damaged skin with Eca, treating with antagonists and incubating in either potting compost or outside in field soil. Mainly fluorescent pseudomonads, pre-screened for in vitro antagonistic activity on agar and high soft rot reducing ability on tuber slices, were tested in the mini-tuber bioassay. Strains giving the highest degree of wound protection were further tested individually and in combination under field conditions in the young tuber bioassay. One individual strain and two combinations, resulting in reduction of contamination levels on skinned surfaces of 85% and between 60% and 70%, respectively, show good potential for biological control of blackleg.     

Methods for assessing bacterial density on potato tubers

Summary Formulae which determined tuber surface area from tuber dimensions and weight were tested by using samples from three potato cultivars. Surviving populations of a labelled isolate ofErwinia carotovora ssp.atroseptica following planting, and populations of a fluorescent pseudomonad following dusting with a bacterial powder formulation were used to demonstrate the application of these formulae to the calculation of bacterial density on the tuber surface. Results obtained by washing whole tubers using the formulae to calculate the surface area were shown to be comparable in sensitivity with those obtained by dilution-plating of periderm discs of 1cm².     

Effect ofErwinia carotovora subsp.atroseptica on yield of potatoes from cut and uncut seed tubers in Valencia

Summary The effect on the development of blackleg symptoms and on yield of inoculating seed tubers of 15 cultivars withErwinia carotovora subsp.atroseptica (Eca) was investigated. Tubers were planted either whole or as pieces. Eca inoculation reduced the mean yield per plant by 8% for whole tubers and by 12% for cut tubers. There was no correlation between blackleg symptoms and yield loss.     

The association ofErwinia carotovora var.atroseptica andErwinia carotovora var.carotovora with insects in Colorado

Ten genera from 9 families of dipterous insects collected in the field in the San Luis Valley of Colorado were contaminated withErwinia carotovora var.atroseptica (Eca) andErwinia carotovora var.carotovora (Ecc).Erwinia-contaminated insects were collected from settling ponds near potato warehouses, potato cull piles on growers’ farms, municipal dumps, lettuce and potato fields. The percentage of contaminated insects reached 14.5% in early spring but decreased as the season progressed. Insects were more commonly contaminated withEca thanEcc early in the season. Later the proportion of contamination byEcc increased while that ofEca decreased. We suggest that insects may play a potentially important role in the epidemiology of potato blackleg especially in the reintroduction ofErwinia intoErwiniafree potato fields.     

Seasonal incidence and cause of blackleg and a stem soft rot of potatoes in Oregon

Blackleg of potatoes in a center pivot irrigated circle of Kennebec potatoes in Oregon’s Columbia Basin was caused by eitherErwinia carotovora var.atroseptica (Eca) orE. carotovora var.carotovora (Ecc). Eca was recovered only early in the growing season whereasEcc was associated with blackleg symptoms later in the season. A soft rot, atypical of blackleg, was widespread throughout the circle and was most prevalent during the latter part of the growing season. Initially, the vines near the soil surface appeared translucent and watery and were soft and mushy to the touch. The pathogen associated with this symptom was exclusivelyEcc.     

Role of seed tubers in the spread of plant pathogenicStreptomyces and initiating potato common scab disease

The influence of tuber-borne pathogenicStreptomyces on potato common scab incidence in daughter tubers was examined under micro-plot conditions. Visually healthy tubers, surface-disinfested healthy tubers, and tubers with 25% scab coverage were planted in pasteurized soil. At 30, 57, and 93 days after planting, soil and belowground plant parts were sampled from various zones around the mother tuber. The total population of actinomyctes was determined by plating on a semiselective medium, and colonies of pathogenicStreptomyces were identified using polymerase chain reaction (PCR) targeting thetxtA gene. At day 30, pathogenicStreptomyces populations were below detectable levels, whereas by day 93, measurable levels were present on the belowground plant parts and in soil adjacent to scabby mother tubers at 10⁴ to 10⁵ CFU g^?1 soil. Incidence of scab in the progeny tubers was 89% at harvest. Progeny tubers produced by visually healthy seed tubers had an incidence of 60% scab and substantial populations of pathogenicStreptomyces were present in the zone near the mother tuber (10⁴ CFU g^?1 soil). Plots planted with surface disinfested seed tubers had a very lowStreptomyces population in the tuber zone and yielded 100% marketable tubers. A perfect correlation (r = 1.00) was found between the population densities of pathogenicStreptomyces in the root zone and daughter tuber disease incidence indicating that measurement of such populations in the field can serve as an excellent predictor of scab disease. After harvest, populations of pathogenicStreptomyces (10⁶ to 10⁷ CFU g^?1 lesion tissue) remained high on the mother tubers.     

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.