The influence of tuber position on periderm calcium content and its relationship to soft rot susceptibility

Summary Calcium levels in the periderm of tubers (cv. Sebago) growing in irrigated sands were influenced by the stem position at which the tuber grew, but the effect was not consistent over two seasons. Calcium levels were increased at all tuber positions by addition of calcium to soil; combined treatments of gypsum (1400 kg Ca²⁺/ha) pre-plant and calcium nitrate (37 kg Ca²⁺/ha) side dressings gave the greatest response. Percentage incidence of soft rot lesions caused byErwinia chrysanthemi pv.zeae was not influenced by periderm calcium content. The severity of infection (weight of tissue macerated within 48 h at 30°C) was significantly reduced only by the pre-plant gypsum treatment, but there was no correlation with calcium content of the periderm. Calcium levels in periderm tissue (60–208 mg Ca²⁺/100g) are within the range of published data for other cultivars and results support previous reports that the correlation between tuber susceptibility toErwinia spp. and periderm calcium content is inconsistent.     

Induction of systemic resistance in potato (Solanum tuberosum L.) plants to late blight by local treatment withPhytophthora infestans (Mont.) de Bary,Phytophthora cryptogea Pethyb. & laff. or dipotassium phosphate

Summary Induced systemic resistance to late blight was found in the potato cultivar Bintje which has no major or minor resistance genes to late blight. The prerequisite was a local inoculation with 5×10³ zoospores/mo, ofPhytophthora infestans race 1, 3, 4, 7, 8, a local inoculation with 2×10³ zoospores/ml ofPhytophthora cryptogea isolated from wheat or local treatment with 50–100 mM solution of K₂HPO₄. Potato plants used in the experiments were propagated in vitro from nodal cuttings. Protection caused by the different inductions was 30 to 70% (assessed as a reduced number of lesions/plant and reduced necrotic tissue/leaf or plant) and tended to positively influence yield and dry matter of the haulm. The induced protection in the potato plant was better in young developing leaves than in fully expanded leaves.     

Stimulation of Ca2+ uptake into micropropagated potato plantlets by UV light and vitamin D3

Micropropagated potato plantlets (Solanum tuberosum cvs Acadia Russet, Red Gold, Red Pontiac, and Russet Burbank) were used to test the effects of exposure to ultra violet rays (UV) or inclusion of vitamin D₃ (cholecalciferol) in the test solution on plantlet calcium (Ca) uptake. Ca uptake was determined by measuring shoot tissue⁴⁵Ca²⁺ concentration inex vitro plantlets placed into test solutions containing radiolabelled calcium (⁴⁵CaCl₂). Shoot tissue⁴⁵Ca²⁺ concentration was very significantly increased in all cultivars exposed for 24 h to UV treatment compared with control plantlets. This increase in shoot⁴⁵Ca²⁺ concentration was similar (three cultivars) or greater (one cultivar) than that caused by 10 ing L^?1 vitamin D₁ in the test solution. When plantlets were exposed to UV, then placed for 24 h in the dark, significantly greater shoot⁴⁵Ca²⁺ concentrations occurred compared with plantlets tested immediately following treatment. This suggests that a change in the UV-elicited cellular product occurred during the dark interval that promoted more Ca uptake into plantlets.     

Effect of haulm treatment and harvest time on incidence of tuber rots of potato (Solanum tuberosum L.) after standard wounding and on frequency of stem lesions caused byPhoma foveata Foister

Summary Various haulm treatments and harvest times differentially influenced the incidence of storage rots in potato tubers (Solanum tuberosum L.) in field experiments in Sweden performed over 4 years. The incidence of gangrene caused byPhoma foveata Foister (Phoma exigua var.foveata (Foister) Boerema) increased in cv. Bellona after spraying haulms with diquat as did the amount of infection caused byFusarium avenaceum (Corda ex. Fr.) Sacc. in all three cultivars (Bintje, Bellona, and Magnum Bonum). The lowestP. foveata infection levels occurred after pulling haulms. Late harvesting increased the frequency ofP. foveata in cvs Bintje and Bellona both at 2 and 4 wks interval between haulm treatment and harvest. Tuber and visible stem infection caused byP. foveata were correlated for cvs Bintje and Bellona, but not for cv. Magnum Bonum. The possible relation between tuber and stem infection is discussed.     

Physiological effects of calonyctin on development and yield of potato

Summary Foliar sprays of calonyctin, a natural plant growth regulator extracted from the leaves ofCalonyction aculeatum (L.) House, at a concentration 0.05 activity units, increased the tuber yield of six potato (Solanum tuberosum L.) cultivars by 7–19% (mean 15%) during 1993 and 1994. Physiological differences between calonyctin-treated and untreated potato plants were usually detected 30–40 days after spraying them with calonyctin. The chlorophyll content of treated potato leaves increased, and the chlorophyll a:b ratio decreased. By 40 days after treatment the root oxidizability and soluble protein contents of different parts of the plants also increased. Their subsequent decline as the plants aged was inhibited by calonyctin. It is concluded that calonyctin delayed the senescence of potato plants and increased tuber growth at later stages of development.     

The effect of boron on calcium uptake and growth in micropropagated potato plantlets

Summary Boron (B) requirements differ widely among plant species and the concentration range between toxicity and deficiency is less for B than for any other nutrient. Excess B can adversely affect calcium (Ca) uptake and plant growth. Potato cvs Bintje and Norland plantlets were micropropagated on Murashige & Skoog (MS) nutrient medium, supplemented with 3 (MS control level) or 9 mM Ca, and a range of H₃BO₃ levels (0.025 to 0.300 mM B). Medium B levels of 0.100 and 0.300 mM decreased Ca content in leaves and shoots of cv. Norland, but not Bintje. Medium B level of 0.025 mM, which is 25% of the control MS level, enhanced Ca uptake in cv. Norland and did not compromise normal plantlet growth in either cultivar. This lower H₃BO₃ level (0.025 mM B), and a B-free gelling agent such as Gelrite, could be used for micropropagation of potato and possibly other species susceptible to Ca defifiency disorders.     

Testing the resistance to silver scurf in commercial potato cultivars under controlled environmental conditions

Summary Optimum storage conditions to identify resistance to silver scurf among commercially grown potato cultivars were determined in a series of experiments. Inoculation of field-grown tubers with a conidial suspension ofH. solani (concentration 10⁴ conidia per ml of water) and incubation at 15°C with 95% RH for 1 month followed by 2 months at 85% RH produced the greatest differences in disease severity between potato cultivars. Results with glasshouse-grown tubers were comparable with those from field-grown tubers, indicating that the test could be used to identify resistance in wild species of potato and to understand the inheritance of this resistance.     

The effect of netted scab (Streptomyces spp.) andVerticillium dahliae on growth and yield of potato

Summary The effect ofStreptomyces spp. (netted scab) on the growth of potato was investigated in three pot experiments, in two of which the effect ofVerticillium dahliae was also assessed. The netted scab organisms attacked all underground plant parts of susceptible potato cultivars early in the growing season; the roots were especially seriously attacked, markedly reducing tuber yield and number but prolonging the duration of the growing season. The nematicide oxamyl had little effect on the incidence of netted scab. Repeated growing of the susceptible cv. Bintje greatly increased soil contamination with the netted scab pathogens. V. dahliae reduced haulm growth before wilt symptoms were evident and it reduced tuber yield but not number. Oxamyl delayed infection byV. dahliae by controlling parasiticPratylenchus nematodes (mainlyP. thornei).     

Cell and nuclear degradation in root meristems following exposure of potatoes (Solanum tuberosum L.) to salinity

Summary In many plant species, it has been demonstrated at the whole plant level that supplemental Ca²⁺ alleviates the effects of salinity stress. These effects have been attributed to physiological processes, but there are no reports of the effects of supplemental Ca²⁺ on preventing nuclear damage to the root meristematic cells following exposure to NaCl salinity. Two in vitro cultured potato (Solanum tuberosum L.) cultivars, analysed by fluorescent microscopy and flow cytometry, showed a similar pattern of salinity-induced changes to the nuclei of root meristematic cells. Damage occurring after only a few hours was followed by nuclear degradation at 24 h. Flow cytometry histograms showed a reduction in G1 and G2 nuclei and an increase in degraded nuclei, in NaCl-stressed roots. Salinity-induced nuclear degradation was alleviated by the addition of CaCl₂.     

The Effect of Nitrogen Rate on Vine Kill,Tuber Skinning Injury,Tuber Yield and Size Distribution,and Tuber Nutrients and Phytonutrients in Two Potato Cultivars Grown for Early Potato Production

Early potatoes are typically produced using less nitrogen than a full season potato crop as high rates of nitrogen may delay tuber set and lead to excessive vine growth that is difficult to terminate prior to harvest. Bintje and Ciklamen potato cultivars were grown with preplant soil nitrogen levels of 34 to 38, 67, and 101 kg N ha^-1 in 2013 and 2014 near Paterson, Washington. Nitrogen rate had little impact on the number of tubers and stems per plant of both cultivars, but increasing nitrogen rate tended to increase leaf area of both cultivars. Vine desiccation of Bintje with diquat was less complete as nitrogen rate increased, while Ciklamen vine kill was reduced by higher nitrogen in 1 of 2 years. Tuber skinning injury, tuber weight loss, and tuber size distribution were not affected by nitrogen rate. Tuber skinning injury and tuber weight loss were reduced in both cultivars by harvesting at 4 weeks after initial vine kill compared to harvesting at 2 weeks after vine kill. Total tuber yield was lower for both Bintje and Ciklamen in 1 of 2 years at the 34 to 38 kg N ha^-1 rate. Tuber nitrogen and zinc levels tended to increase with increasing nitrogen rates, while most other nutrients, vitamin C, total phenolics, and antioxidant capacity showed little response. It appears that 67 kg N ha^-1 provides adequate nitrogen to produce a good tuber set and yield of small tubers while not producing excessive vine growth that may be more difficult to kill.     

Effect of Calcium Concentration in Growth Medium on Oxalate Content and Evaluation of the Role of Guttation in the Regulation of Oxalate in Eddo

The effects of calcium concentrations in the growth medium on oxalate content of leaf blades, petioles and corms and the involvement of guttation in the regulation of oxalate homeostasis were investigated in eddo (Colocasia esculenta (L.) Schott var. antiquorum Hubbard & Rehder). The plants were grown hydroponically in solutions containing 0 mM calcium, 1 mM calcium nitrate (control), 15 mM calcium nitrate or 15 mM calcium chloride. Total oxalate content (soluble plus insoluble) of leaf blades, petioles and corms did not differ with the calcium concentration in solutions containing 1 mM or 15 mM calcium nitrate or 0 mM calcium. The soluble oxalate content of these parts decreased as the calcium concentration of the solution was increased. Solutions containing 15 mM calcium nitrate or 15 mM calcium chloride gave a significantly lower proportion of soluble oxalate content to total oxalate content in each part, especially in leaf blades than 0 mM calcium or 1 mM calcium nitrate. In contrast, a positive correlation was found between insoluble oxalate content and calcium concentration in the solution. These results demonstrate that high calcium concentrations in the growth medium reduce soluble oxalate content of the plant. Soluble oxalate was detected in eddo guttation fluid. Soluble oxalate content in this fluid (mg mL^?1) and the amount of soluble oxalate exuded by guttation (mg leaf^?1 night^?1) were significantly lower in the solutions containing 15 mM calcium than in those containing 0 mM and 1 mM calcium. These results indicate that guttation may affect the concentration of soluble oxalate in the plant bodies although not strongly contributing to a decrease in soluble oxalate content in eddo grown under high calcium conditions.     

Relative salinity tolerance of potato cultivars assessed byin vitro screening

One hundred and thirty European and North American potato cultivars were assayedin vitro for salinity (NaCl) tolerance. A modified single-node cutting bioassay was used in which cultivars were exposed to a range of NaCl levels (0, 40, 80, and 120 mM), in a Murashige and Skoog-based medium, for 1 month. Evaluations were performed twice for each cultivar at each salt level, using five single-node cuttings. Six vegetative growth parameters (shoot and root lengths, fresh and dry weights) were measured at the time of harvest and corrected for differences in cultivar vigor. These relative values were subjected to multivariate cluster analysis. The sum of the relative rankings at 40, 80, and 120 mM NaCl partitioned the cultivars into 8 units. The cultivars Amisk, BelRus, Bintje, Onaway, Sierra, and Tobique were in the most salinity tolerant unit and in the top cluster group for vigor with the exception of Tobique. These cultivars can be recommended for further study.     

Comparative susceptibility of some potato cultivars to dry rot caused byFusarium sulphureum andF. solani var.coeruleum

Summary The susceptibility of 15 potato cultivars to dry rot caused byFusarium sulphureum andf. solani var.coeruleum was examined over 8 years. Tubers were wounded, inoculated, incubated at 10°C for 7–8 weeks and the size of the rot assessed.F. sulphureum was the more aggressive species. There was little correlation between the rank order of susceptibility of the cultivars to the two pathogens, but a higly significant correlation between years. Two years' tests are deemed sufficient to assess susceptibility to both species.     

Calcium translocation and accumulation into potato tubers

Summary Calcium uptake into potato plants was examined using test solutions containing 5% safranin dye (C₂₀H₁₉N₄C1 mw 350.85) and the radiotracer⁴⁵CaCl₂. When minitubers were suspended in test solutions for up to 5 days, safranin moved into the outer pith tissues while⁴⁵Ca²⁺ was located throughout the pith. Ca²⁺ is apparently taken up directly from the tubersphere by a slow diffusion process. Plantlets with one microtuber were used to investigate calcium uptake via basal roots.⁴⁵Ca²⁺ was well ahead of the safranin dye front in all plantlet stems.⁴⁵Ca²⁺ in shoot tips was significantly greater than in microtubers and no safranin entered the microtubers. Greenhouse-grown ex vitro plantlets with minitubers attached were used to determine the relative uptake by basal and stolon roots. Basal root feeding contributed significantly more⁴⁵Ca²⁺ to shoot tips and tubers than stolon root feeding while combined feeding gave the greatest shoot tip and tuber⁴⁵Ca²⁺ levels.     

Response of ten potato cultivars to temperature as measured by chlorophyll fluorescencein vivo

Forty-day-old plants of ten cultivars of potato,Solanum tuberosum L. (Alpha, Atlantic, Bintje, Caribe, Kennebec, Red Pontiac, Russet Burbank, Sebago, Shepody and Superior), were placed into a controlled environment chamber held continuously at 35 C and their growth (Plastochron Index) and several chlorophyll fluorescence parameters (O, P, T, Fv and Fr) were measured after 1, 14, 21 and 28 days’ exposure. The cultivars were grouped according to heat tolerance based upon survival of three of four plants. The least heat tolerant group, surviving 14 days, included Atlantic, Bintje and Superior. The medium heat tolerant group, surviving 21 days’ exposure, included Kennebec, Red Pontiac and Sebago. The best heat tolerant group, surviving 28 days’ exposure, included Alpha, Caribe, Russet Burbank and Shepody. In addition, chlorophyll fluorescence parameters of six plants of each cultivar were also measured after 1 h at 5, 15, 25 and 35 C exposure in a second experiment. In all cases plants in the group with the least tolerance displayed less fluorescence than the medium or high heat tolerance plants, suggesting that plants with the least tolerance to high temperature exposure had less energy transfer through PSII (Photosystem II). These plants also had a rise in T at temperatures aboveca. 15 C. A decrease in Fv during growth at 35 C was a good indicator of foliar heat damage. Chlorophyll fluorescence of plant tissue in all three groups increased after short exposure of 1 h to temperatures below 15 C and also after continuous exposure to 35 C. At both ranges of temperature, damage was probably occurring to the thylakoid membranes which inhibited re-oxidation of PSII. Since the rate of response was different, chilling and high temperature apparently differ in how they alter the thylakoid membranes.     

Production of phytoalexins, glycoalkaloids and phenolics in leaves and tubers of potato cultivars with different degrees of field resistance after infection withPhytophthora infestans

Summary The kinetics of accumulation of phytoalexins, glycoalkaloids and phenolics was studied in two potato cultivars differing in their degrees of field resistance when infected withPhytophthora infestans. Tuber slices and leaves of cvs Pampeana INTA (high degree of field resistance, free of R genes) and Bintje (susceptible) were infected with race C (complex race 1, 3, 5, 7, 11) ofPhytophthora infestans. Phytoalexins and phenolics accumulated in tuber and leaf tissues which had been inoculated. The levels of these compounds in the susceptible cv. Bintje were relatively low and similar to those found before inoculation. Leaves of cv. Pampeana INTA had a very high glycoalkaloid content, suggesting that glycoalkaloids may play a role in protection of leaves against the fungus. However, we could find no correlation between resistance and glycoalkaloid content of tubers. Our results suggest a major role of phytoalexins, phenolics and glycoalkaloids in the complex mechanisms of field resistance.     

Transgenic potato plants expressing oxalate oxidase have increased resistance to oomycete and bacterial pathogens

Summary Potato (cv. Bintje) was transformed with a gene encoding an oxalate oxidase from wheat under the control of the CaMV35S promoter. Transgenic potato plants produced high constitutive levels of H₂O₂ as visualized by 4-chloro-l-naphtol staining. The resistance of these plants was tested againstPhytophthora infestans. An increased level of resistance to the disease was marked by a reduced number of lesions as well as by a decreased number of sporangia formed per lesion. In addition, oxalate oxidase overexpressing plants also exhibited improved resistance toStreptomyces reticuliscabiei, the causal agent of netted scab. Increased expression of oxalate oxidase had no effect on the interaction withErwinia carotovora. These experiments show that overexpression of oxalate oxidase represents a potentially interesting approach for protection of potato to pathogens.     

Potato growing in short rotations and the effect ofStreptomyces spp.,Colletotrichum coccodes,Fusarium tabacinum andVerticillium dahliae on plant growth and tuber yield

Summary The yield of potatoes decreased as the frequency of growing this crop in a rotation increased, even in the absence of well-known soil pathogens e.g.Globodera spp. Soil disinfection with methylbromide or pasteurization at 60°C with steam for 30 min eliminated the rotation effect on yield, suggesting that it was caused by a complex of microbial pathogens. Organisms thought to belong to the complex wereC. coccodes, F. tabacinum, V. dahliae andStreptomyces isolates causing russet (netted) scab. Their effects on growth and yield were studied in non-sterilized soil that had never carried a potato crop before.V. dahliae decreases the yield of susceptible potato cultivars,C. coccodes may cause damage only late in the growing season in weakened plants. In the highly susceptible cv. Amethyst yield loss byV. dahliae was almost doubled in the presence ofC. coccodes. F. tabacinum did not influence growth and tuber yield neither singly nor in combination with other pathogens. TheStreptomyces isolates cause extensive root damage and yield loss in susceptible potato cultivars.

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Zusammenfassung Kartoffelpflanzen aus einem Boden mit Kartoffeln in der Fruchtfolge (Frequenz 1:3) zeigten, verglichen mit der Ertragsleistung von Kartoffeln aus einem Boden ohne bisherigen Kartoffelanbau, einen auff?lligen Ertragsverlust an Gesamttrockensubstanz (Abb. 1 und 2). Auch die N?hrstoffaufnahme war hier signifikant verringert (Abb. 3 und 4). Ertragsleistung und N?hrstoffaufnahme liessen sich jedoch durch Desinfektion des Bodens mit Methylbromid und durch Dampfsterilisation oder durch Pasteurisierung verbessern (Abb. 1, 2, 3 und 4). Inokulationen des Bodens ohne bisherigen Kartoffelanbau mitFusarium tabacinum oderColletotrichum coccodes beeinflussten den Knollenertrag nicht (Tab. 2), w?hrend Inokulationen mit Schorferregern (Streptomyces spp.) 14% weniger Knollenertrag verursachten, die Anzahl der Knollen verminderten (Tab. 2) und das Pflanzenwachstum sowie die Abreife der Pflanzen (sorte Bintje) beeinflussten (Tab. 4 und 5). Obgleich sichF. tabacinum bei enger Fruchtfolge an den Wurzeln der Kartoffelpflanzen manifestiert, kann es hier nicht als Pathogen betrachtet werden. Inokulationen mitC. coccodes, Verticilium dahliae undStreptomyces (Netzschorfisolate) in die für diese Pathogene unterschiedlich anf?lligen Sorten Bintje, Amethyst und Mirka ergaben einen Ertragsverlust bei den fürStreptomyces oderV. dahliae empfindlichen Sorten; ausserdem wurde ein durchC. coccodes verursachter synergistischer Effekt an den vonV. dahliae hervorgerufenen Sch?den in der Sorte Amethyst beobachtet (Tab. 5). In der Sorte Bintje wurde die Knollenzahl nur dann verringert, wennStreptomyces dabei beteiligt war (Tab. 6). Netzschorf kann als Fruchtfolgekrankheit betrachtet werden (Tab. 7).

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Résumé Le rendement en matière sèche totale est considérablement réduit lorsque l'on compare la productivité d'une culture de pomme de terre dans une rotation de 3 ans à celle d'un sol non cultivé en pommes de terre au préalable (fig. 1 et 2). De même l'absorption des éléments nutritifs est réduite de fa?on significative dans les sols à pommes de terre (fig. 3 et 4). La productivité et l'absorption peuvent être retrouvées par la désinfection du sol au bromure de méthyle, la stérilisation à la vapeur ou la pasteurisation (fig. 1, 2, 3 et 4). L'inoculation avecFusarium tabacinum ouColletotrichum coccodes dans un sol n'ayant pas re?u de pommes de terre, n'a aucune influence sur le rendement en tubercules (tabl. 1) alors que l'inoculation avec la gale commune russet scab provoqué parStreptomyces spp. provoque une perte de rendement en tubercules de 14%, une diminution du nombre de tubercules et modifie le développement et la maturité des plantes (tabl. 3 et 4) avec la variété Bintje.F. tabacinum, quioque présent sur les racines de pommes de terre dans les rotations courtes, ne peut être considéré comme un pathogène de cette culture. L'inoculation avecC. coccodes, Verticillium dahliae etStreptomyces (isolats de gale commune provoquant le russet scab) des variétés Bintje, Amethyst et Mirka, de sensibilité différente pour ces pathogènes, se traduit par une diminution de rendement pour les variétés sensibles àStreptomyces ouV. dahliae et par un effet de synergie deC. coccodes pour les dommages causés parV. dahliae sur la variété Amethyst (tabl. 5). Le nombre de tubercules de la variété Bintje n'est diminué qu'en présence deStreptomyces (tabl. 6). La gale commune (russet scab) peut être considérée comme une maladie de rotation (tabl. 7).

     

Field performance of potato microtubers as propagation material

Summary In five field trials with the cultivars Gloria (early), Bintje (mid-early) Désirée (mid-late) and Morene (late), crops grown from conventional 28–35 or 35–45 mm seed were compared with crops grown from microtubers, of various sizes and from various sources, that had been producedin vitro. The following means to quicken initial crop development from the micropropagated material were tested: large microtubers, plastic soil cover, and transplanting of plantlets grown from microtubers pre-planted in a glasshouse. Crops grown from microtubers weighing less than half a gram yielded much less than crops grown from conventional seed crops but their yields were increased by each treatment. With the later-maturing cultivars, which generally produce few tubers per plant, the yields within seed grades from plants grown from transplanted microtuber plants were comparable with those of conventional crops. Reasons are given, why direct planting of microtubers, with or without plastic foil, is not a practical option.