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.     

Penetration of potato tuber lenticels by bacteria in relation to biological control of blackleg disease

Summary In a glasshouse experiment three potato cultivars were grown to maturity in wet or dry compost. The number of lenticels per tuber was greater with larger tubers but was unaffected by the cultivar or soil moisture regime. The frequency of lenticel penetration by a water soluble stain, safranin O, remained high as tubers developed to maturity in wet soil. In dry soil penetration declined markedly as the tubers matured. When tubers, harvested just before the onset of haulm senescence, were inoculated withErwinia carotovora ssp.atroseptica, the frequency of lenticel rotting was less than the rate of stain penetration, indicating that additional factors were involved in the bacterial infection process. Inoculating mature tubers with bacteria and incubating them in anaerobic conditions frequently resulted in rotting of the lenticels. Comparable tubers incubated in aerobic conditions showed no rotting or invasion by bacteria. The results are discussed in relation to the biological control of blackleg.     

Erwinia carotovora subsp.atroseptica infection promotes verticillium wilt development in potato in Israel

Summary The interaction betweenErwinia carotovora subsp.atroseptica (Eca) andVerticillium dahliae and its effect on symptom development in potato cultivars showing different degrees of resistance to them was examined over two seasons in irrigated fields in a hot, dry climate. Four cultivars were used: Cara, highly resistant to blackleg and tolerant to Verticillium wilt; Pentland Crown also resistant to blackleg but susceptible to Verticillium wilt; Désirée, moderately susceptible to blackleg but tolerant to Verticillium wilt; and Maris Bard, susceptible to both diseases. Seed tubers were inoculated with Eca immediately after harvest in Scotland, to simulate natural infection, and then planted in Israel in soil naturally infested byV. dahliae. In Verticillium tolerant cultivars, Eca infection increased the rate of colonization byV. dahliae and significantly enhanced symptom development, as assessed by suppression of plant height and wilt symptoms. This report is a portion of the Ph.D. thesis of the senior author in Ben-Gurion University of the Negev.     

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.     

Assessing six Austrian potato cultivars for resistance toErwinia carotovora subsp.atroseptica

Summary The susceptibility of six new Austrian cultivars to soft rot, stem rot and blackleg caused byErwinia carotovora subsp.atroseptica was assessed over 2 years in two locations. Soft rot susceptibility was assessed by whole tuber and half tuber tests, stem rot by stem inoculation and blackleg by planting inoculated tubers in the glasshouse. The susceptibility of the cultivars tested with the tuber and blackleg test methods were in general agreement. The half tuber test was more precise in differentiating intermediate levels of susceptibility than the whole tuber test. The reaction of the cultivars to soft rot could be classified as susceptible (Gina and Romina), moderately susceptible (Ditta, Sonja and Bintje), or slightly susceptible (Treff, Komet and Désirée). Results from the stem rot test did not agree with this classification and also depended upon the physiological state of plants as influenced by growing season and glasshouse conditions.     

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.     

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.     

Effects of contamination byErwinia carotovora subsp.carotovora andE. carotovora subsp.atroseptica of potato seed tubers and of cultivar resistance on blanking or nonemergence and blackleg development in Valencia,Spain

Summary High grade potato seed tubers of three cultivars were inoculated in Scotland by vacuum infiltration in suspensions ofErwinia carotovora subsp.carotovora and subsp.atroseptica in different combinations, and transported to Valencia, Spain. They were cut into two to three pieces and planted in January 1984, 1985 and 1986 in fields furrow irrigated before and after emergence. High incidences of blanking and blackleg were associated with seed inoculated with high numbers ofE.c. atroseptica alone or together withE.c. carotovora and not with high or low numbers ofE.c. carotovora alone.E.c. atroseptica predominated at emergence in March in rotting seed pieces which failed to produce a plant, regardless of the seed treatment, and in diseased stems in April but it was replaced byE.c. carotovora in May. The levels of blanking and blackleg after inoculating 16 cultivars with both erwinias were not correlated between years nor were they significantly different within years among most of the cultivars.     

Effect of acetylsalicylic acid on soft rot produced byErwinia carotovora subsp.carotovora in potato tubers under greenhouse conditions

Summary The efficiency of acetylsalicylic acid (ASA) in inducing localised acquired resistance against infection byErwinia carotovora subsp.carotovora was evaluated by treating potato tubers with ASA at three concentrations. Three days after treatments, tubers were inoculated withE. carotovora subsp.carotovora by wound inoculation or by irrigation with a bacterial suspension. Experiments were performed for two consecutive years. Statistical analysis revealed that treatment of tubers by immersion in ASA solutions at low concentrations induced a significant reduction in the soft rot incidence. Wounding of the tubers was the most effective inoculation method and ASA at concentration of 0.0125% (w/v), pH 7 was more efficient than at 0.025 or 0.05%. No phytotoxicity of such treatment was observed.     

Factors influencing the control of potato gangrene by fungicide treatment

Summary Potato tubers inoculated withPhoma exigua var.foveata were dipped or sprayed with fungicide immediately after wounding or after holding them at 5 or 15°C for up to 14 days. Thiabendazole and 2-aminobutane, either separately or combined, controlled gangrene when applied soon after wounding: on tubers with little inoculum, application in 2 litres t¹ was better than in 400 ml t⁻¹. When treatment was delayed, 2-aminobutane or the mixture was more effective than thiabendazole alone. Adsorption of thiabendazole onto soil increased with decreasing soil pH and the fungicide gave better control of disease on tubers carrying neutral than acid soil. Treating tubers with dichlorophen increased gangrene.     

Lightning damage to potatoes

Summary Two distinct round patches were observed in a potato field where the haulm showed symptoms like those of blackleg. The remainder of the field was in vigorous growth. Affected stems had long cracks andErwinia carotovora var.atroseptica was isolated from some. This had probably developed subsequently on damaged tissue and no rotting was apparent below soil level. Most of the tubers were decayed but noErwinia and only green pseudomonads were detected. Local meteorological records showed that thunderstorms occurred on only one day (1 August) in the six weeks before observation of the field symptoms. It was concluded from all evidence that the condition described was caused by a lightning strike on that day.     

Expression of the chicken lysozyme gene in potato enhances resistance to infection byErwinia carotovora subsp.atroseptica

Infection of potato plants and tubers with the bacteriumErwinia carotovora subsp.atroseptica produces blackleg and soft rot diseases, which cause significant losses to crops and stored potatoes. In order to obtain resistance against this bacterium, the genechly encoding the enzyme lysozyme from chicken was introduced into potato plants (cv. Desirée) viaAgrobacterium- mediated transformation. Sixty-three and 69 transgenic potato clones were evaluated in the greenhouse for resistance to blackleg and soft rot diseases, respectively. Results reported in this paper indicate that 21%-29% of the potato clones showed increased resistance to infection by the bacteriumE. c. subsp.atroseptica T7, as revealed by a reduced severity of blackleg or soft rot symptoms. Nine clones showing different levels of resistance were selected for further molecular analysis. The number of copies of the transgene integrated in the plant genome of these clones was estimated by Southern blot analysis. The level of transgene expression, detected by Northern blot analysis, correlated with the level of resistance detected in these clones.     

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.     

Resistance toErwinia carotovora subsp.atroseptica in second backcross populations of somatic hybrids betweenSolanum tuberosum andS. brevidens

Summary Eleven clones obtained from a cross between cv. Katahdin and fusion products betweenSolanum tuberosum and the non tuber-bearing speciesS. brevidens, were backcrossed again withS. tuberosum (clone AR80-127-5). Small tubers harvested from 583 seedlings of these second backcross (BC2) populations were screened for tuber tissue resistance toErwinia carotovora subsp.atroseptica under aerobic conditions. After multiplication in the field. BC2 clones again were screened for soft rot resistance under aerobic as well as anaerobic conditions. In general, the resistance of the BC2 populations was reduced in comparison with the BC1. Variation for resistance was found within the BC2 populations, but there was no correlation between the results of the three tests performed. Four BC2 populations were also screenned for resistance to blackleg in the field. Significant differences were found between populations for mean percentage of diseased plants, but these differences could not be explained by the resistance of the parental clones.     

Control of potato blackleg by tuber pasteurisation: the determination of time-temperature combinations for the inactivation of pectolytic erwinia

Summary Pasteurisation of potato tubers by immersion in hot water is being examined as a method of blackleg control. Studies on the in vitro heat resistance of representative pectolytic erwinia have enabled prediction curves for the selection of suitable times and temperatures of pasteurisation to be prepared. High levels of contamination on some tubers may require heat treatment that will reduce the erwinia population by more than 80% to ensure that only innocuous levels remain.     

Long-day-adaptedSolanum phureja as a source of resistance to blackleg caused byErwinia carotovora subsp.atroseptica

Summary Long-day-adaptedSolanum phureja clones were assessed for resistance to blackleg caused byErwinia carotovora subsp.atroseptica under field and controlled environmental conditions over two years. In the field, twenty-two of the twenty-three clones ofS. phureja assessed were as resistant to blackleg as the commercial cultivar Ailsa, the most resistant control, and were significantly (P<0.001) more resistant than the intermediate and susceptible cultivars Wilja and Estima, respectively. Under controlled environmental conditions, resistance in commercial cultivars was more easily overcome. However, 18 of the 21S. phureja clones assessed were significantly more resistant to blackleg than these cultivars.     

Slug damage and control of field slug (Deroceras reticulatum (Müller)) by carvone in stored potatoes

Summary After a wet autumn and harvesting under wet conditions, slugs brought into potato stores via clods and soil adhering to tubers may cause substantial damage by feeding on the tubers. A carvone sprout inhibitor, Talent^?, applied in the potato stores at a dose of 50 ml per tonne potatoes, controlled slugs within a few days. A dose of 25 ml carvone was insufficient. Using a laboratory box test, the slug (Deroceras reticulatum) affected only wounded tubers and, although slime was present on the unwounded potatoes, they were not damaged by slugs.     

Growth Stage of Cyperus esculentus Influences Its Allelopathic Effect on Ectomycorrhizal and Higher Plant Species

Summary

Live plants and plant material in various forms have important roles in ecological processes. Weeds may be involved in interactions with desirable species at different trophic levels through the production and release of allelochemicals. The allelopathic potential of the weed Cyperus esculentus (yellow nutsedge) was assessed by preparing aqueous extracts from tubers and foliage from immature or mature plants, and testing their effects on an ectomycorrhiza and two higher plant species. The extracts from tubers and both foliage types significantly reduced the colony diameter of the ectomycorrhiza Boletus maxaria, which was isolated from roots of the forestry species Pinus patula, on agar medium. Extracts (2% m/v) from C. esculentus tubers and the foliage of immature plants inhibited the germination of lettuce (Lactuca sativa) seeds significantly. At 5% concentration, the extracts from foliage of immature weed plants completely inhibited the germination of lettuce seeds at the end of the 7-day trial period. The emergence of corn (Zea mays) was retarded in soil where C. esculentus tubers were planted 28 days before planting the crop, irrespective of whether the weeds continued to grow or were physically removed at the time the corn was sown. In contrast, where weed tubers and corn seeds were planted at the same time, emergence of corn was not affected. It is suggested that the growth stage of weeds be considered in the assessment of their direct and indirect allelopathic effects, and in predictions for their impacts on crop development and yield.     

Optimisation of sample size for the detection of latent infection byRalstonia solanacearum in potato seed tubers in the highlands of Peru

Summary A sampling strategy was evaluated in the Andean highlands of Peru to optimise the detection ofRalstonia solanacearum in seed tubers harvested from symptomless crops. A sensitive and specific serological method developed at CIP was used to detect the pathogen in latently infected tubers. Optimum sample size was evaluated for symptomless crops after analysing various numbers of composite samples and using a binomial distribution model to calculate the detection probabilities.R. solanacearum was detected in all lots from fields with visible symptoms, so validating the detection technique. About half of the seed lots from apparently healthy fields at altitudes of up to 3,100 m were found positive for the pathogen.R. solanacearum was detected with 99% probability in samples of 350 tubers from seed lots from symptomless crops. This number of seed tubers could feasibly be processed in a seed-health test without incurring too high a cost for labour and materials.     

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.