The development of mature plant resistance in four potato cultivars against aphid-inoculated potato virus YO and YN in four potato cultivars

Summary Field-grown potato plants of cvs King Edward, Record, Maris Piper and Désirée were inoculated on seven different dates during the growing season of 1987 and 1988 with either potato virus Y^O (PVY^O) or PVY^N, using three viruliferous peach-potato aphids (Myzus persicae) per plant. In each cultivar, the proportion of progeny tubers infected with PVY^O or PVY^N was high in plants inoculated during the four weeks following emergence, the proportion declining to zero or close to zero in the subsequent 4–6 wks.     

The conservation of potato cultivars

Summary To prevent the loss of important genetic information cultivars are conserved in several collections of gene banks. In principal, there are two options for the medium to long-term storage of potato cultivars: storage as in vitro plantlets or microtubers and storage of meristems or shoot-tips in liquid nitrogen. In the Braunschweig potato cultivar collection, 360 cultivars are maintained under slow-growth conditions. Ten microplantlets of each cultivar are stored in test tubes containing filter paper bridges and 5 ml Murashige and Skoog (MS) liquid medium. The cultures were maintained at 10°C with a light intensity of 2 klux and 16 hours-day and can be stored under these conditions up to three years. Two hundred and forty-five cultivars are cryostored in liquid nitrogen. About 300 trimmed shoot-tips of each cultivar are incubated in MS-Towill-medium and then transferred into the cryoprotective solution. After an incubation time of about 2 hours trimmed shoot-tips fixed on an aluminium foil were put in cryo vials and stored in a container. The survival rate of the thawed, trimmed shoot-tips varies from 55%–100%. More important for a gene bank, however, is the plant regeneration. The average regeneration of all cultivars is about 40%.     

Glycoalkaloid accumulation during tuber development of early potato cultivars

Summary Plants of early potato cultivars were sampled at successive harvests during tuber development and individual tubers were analysed for α-solanine and α-chaconine using high-performance liquid chromatography. Mean tuber total glycoalkaloid concentration (α-solanine plus α-chaconine) per plant decreased with time and statistically significant differences between cultivars were observed in the patterns of decline during tuber growth. The mean tuber ratio of α-chaconine to α-solanine increased during tuber development and was also affected by genotype. Total glycoalkaloid concentration for individual tubers of marketable sizes (up to 50 g fresh weight) exceeded the safety limit of 20 mg per 100 g fresh weight for cultivars Home Guard and British Queen but not for Rocket. These differences were attributable to differences in both rates and patterns of glycoalkaloid accumulation during tuber development, although in all cultivars results were consistent with glycoalkaloid accumulation occurring in the expanding peripheral cell layers of tubers for a considerable period after tuber initiation.     

Loss of yield in potato selections infested with potato leafhoppers

The loss of yield resulting from infestation with potato leafhoppers,Empoasca fabae (Harris), was measured in a group of potato selections (Solatium tuberosum subsp.tuberosum). For 6 years in which 300 different clones were tested, the average loss of yield was 39%. The correlation over clones between level of infestation and percent hopperburn equaled 0.56; between level of infestation and loss of yield 0.36; and between percent hopperburn and loss of yield 0.41. Each coefficient is significant at P=0.01. Significant differences were found in levels of infestation and in percent hopperburn among the selections, but even those selections with the most resistant foliage had greatly reduced yields when infested. No selections were found that consistently produced a normal yield when infested with leafhoppers. The low level of infestation on the more resistant clones, however, may make chemical control at lower rates more effective.     

Relationship between resistance to late blight in potato foliage and tubers of cultivars and breeding selections with different resistance levels

Due to changes in the pathogen population, late blight of potatoes caused byPhytophthora infestans has become a more difficult disease to manage and there is a need for new potato cultivars with greater and more stable disease resistance. Field studies are required to identify and characterize host resistance to late blight in both foliage and tubers but, as epidemics vary from year to year, combining multi-year results can be difficult. Residual maximum likelihood (REML) was successfully used to analyze data which demonstrated good correlations between foliar and tuber responses to late blight (US-1 genotype). In addition, studies on post-harvest inoculated tubers provided more reliable disease responses than field studies, and the disease resistance with this method correlated well with foliar disease responses. This tuber test would be a useful method of pre-screening selections for disease response prior to testing in the field.     

Predicting yield and processing quality of potato breeding selections

The linear relationship between “site mean” and potato cultivar performance was used to develop predictive models for total yield, yield of US No 1 grade, per cent US No 1 grade, specific gravity and fried chip color. The best fitting linear expression for each of the traits was determined by linear regression for specific cultivars. Common limits for “site means” could then be substituted into the expressions for predictive purposes. Application of this method to large and small data sets demonstrated its use for interpreting preliminary yield trial information for the identification of superior breeding selections.     

Factors influencing PVY development and disease expression in three potato cultivars

Studies were performed to investigate factors affecting symptom expression of potato virus Y infection in three potato cultivars, Russet Norkotah, Shepody, and Red LaSoda. Quantitative enzyme-linked immunosorbent assay (ELISA) results revealed few differences in the relative virus titer among cultivars tested. Potato virus Y (PVY) titers developed as rapidly in Russet Norkotah as in Shepody and Red LaSoda. Additional studies were performed to determine the effect of light intensity and infections of PVY and potato virus X (PVX), alone and in combination, on the expression of mosaic symptoms in these three cultivars. Low light intensity (270-330 uE/m²/sec) significantly increased plant heights and severity of mosaic disease among the cultivars compared to high light intensity (100-200 uE/m²/sec). PVX and PVY, as well as the combination of PVX and PVY in the same plant, decreased plant height compared to the uninoculated (healthy) controls. Low light intensity and dual infections of PVX and PVY significantly increased mosaic disease severity in Shepody and Red LaSoda, but not in Russet Norkotah. Results of these studies refute the suggestion that Russet Norkotah is resistant to PVY infection since virus titers in this cultivar are similar to the known susceptible cultivars Shepody and Red LaSoda. These results further suggest that while Russet Norkotah is fully susceptible to infection by PVY, it resists symptom expression.     

Evaluation of potato varieties and selections for resistance to bacterial soft rot

Potato varieties and selections were evaluated for resistance to bacterial soft rot caused byErwinia carotovora subsp. carotovora and Erwinia carotovora subsp. atroseptica in mist chamber. A randomized complete block design with a single treatment and 3 replications was used in this study. Potato lines were inoculated with bacterial suspension (10 tubers / line) using the puncture inoculation method and incubated for 4 days in a mist chamber at 21 C and 100 % relative humidity in the dark. Although there were differences in incidence of soft rot and in amount of weight reduction, most of the potato lines were susceptible to tuber soft rot. Mean incidence (%) of soft rot ranged from 10 to 100%. Mean reduction of tuber weight (%) ranged from 0.13 to 16.43 %. Among the varieties and selections tested, AF 522-5 was the most resistant to tuber weight loss, while AF 1424-7 was most susceptible. There were also significant differences between years, and a variety by year interaction. Testing over a period of years is recommended. A significant correlation coefficient of soft rot incidence (%) and reduction of tuber weight (%) was obtained (r=0.65; P=0.05), indicating that incidence was a fair measure of soft rot potential. However, the greater variability in results for incidence make weight loss a better measure of soft rot reaction. There was a significant difference among varieties in the reduction of tuber weight when potato lines were inoculated either 1 month or 2 months after harvest, but the interaction of time by year prohibits a conclusion as to which time gives a better test reaction. Late maturing varieties had slightly less weight loss than earlier maturing varieties.     

Ring rot symptom development on potato cultivars and lines in southern Alberta

Summary Plants were grown in the field from seed pieces of potato cultivars injected with ring rot bacteria (Corynebacterium sepedonicum). Symptoms were produced with both 18 and 180 colony forming units (cfu) on cvs Norchip and Red Pontiac and with 180 cfu on cv. Belrus plants. Tuber symptoms were detected in all cultivars except Belrus and Teton. Tuber progeny produced plants that developed top symptoms on all cultivars except those of cv. Nooksack, Russet Burbank, and Teton. Tuber progeny of the second crop produced both plants and tubers with symptoms developing only in the cv. Nooksack. In another 3-year experiment, variability in the disease response of selected cultivars and lines was examined following knife-inoculation of tuber seed with a high level of ring rot bacteria. Significant correlations between top and tuber symptoms were detected, but they were not high enough to make unnecessary the examination of both top and tuber symptoms in ring rot disease selection studies. Contribution no. 3879111     

Dormancy and sprout development of some South African potato cultivars during cold storage

Summary Observations were made on dormancy and sprout growth of nine potato cultivars stored at 3–4°C, 7–8°C and 11–12°C, respectively. Tubers of the cultivar Vanderplank had a very long dormant period (232 days at 3–4°C) and showed little sprout growth at 180 days. The cultivar Koos Smit had a very short dormant period (92 days at 3–4°C) and developed considerable sprout growth at the higher temperatures. The reaction of tubers of Up-to-date and BP₁ were approximately the same, and intermediate between those of Vanderplank and Koos Smit.     

Estimating potato leaf area index for specific cultivars

Summary The growth and duration of crop leaf area determines the amount of solar radiation intercepted by the canopy and therefore influences the extent of photosynthesis, evaporation, transpiration and final dry matter yield. The objective of this study was to develop cultivar specific relationships to estimate the daily leaf area index (LAI) for the potato crop (Solanum tuberosum L.) that included the effects of available soil water. The model is divided into three LAI growth stages, the durations of which are partially related to potato heat units (PHU). The LAI in the first stage is estimated from a cultivar specific leaf area-based radiation use efficiency index with a soil water reduction factor. The second stage involves the maintenance of a constant LAI with the duration related to both PHU and a soil water index that can accelerate senescence. The final stage includes a decrease in the LAI from a maximum to zero in response to a cultivar specific PHU accumulation. Model simulations compared favourably with independent LAI measurements obtained with a LI-COR plant canopy analyzer over two seasons.     

Screening potato cultivars for common scab of potato in a naturally infested field

Summary Twenty seven cultivars of potato were screened for common scab grown in a commercial field in two successive years (1996–97 and 1997–98). Eight cultivars were least susceptible and the others ranged from medium susceptible to very highly susceptible. None of the cultivars was resistant. Most showed a stable resistance reaction in both years.     

Reaction to late blight in response to nitrogen management in Argentine potato cultivars

The objective of this study was to evaluate the reaction to late blight of two potato cultivars in response to nitrogen (N) management under field and in Vitro conditions. In Balcarce trial a reduction in phenols with the addition of excess N was found. Despite the reduction of the concentration of phenols no differences in the relative area under disease progress curve (rAUDPC) were observed between N levels. In Tafí del Valle, the rAUDPC denoted an interaction between cultivar and N level. In Frital, the N0 showed lower rAUDPC than N optimal (Opt) and N excessive (Exc) treatments. In contrast, no differences in rAUDPC between N levels on Pampeana were found. In the detached leaf test, no significant differences between N levels were observed in the threshold of severity of disease and the lesion growth rate. In conclusion, excessive N fertilization did not increase the susceptibility to late blight in this study.     

Evaluation of potato cultivars before and after storage regimes for chipping

An experiment was conducted beginning in 1969 to determine the chipability of several cultivars of potato (Solarium tuberosum) grown under similar cultural regimes at different locations throughout Ohio. The experiment included 19 cultivars and 11 locations. The tubers from a particular location were harvested and transported to the laboratory where a portion was chipped and other portions were stored at 40,45,50, and 55°F for 3 and 6 months and subsequently chipped. The chips were analyzed for color both objectively using the Agtron M-30-A and subjectively using the PC/SFA color chart. In addition, specific gravity and count were also determined before storage. Not all cultivars were included for the duration of the experiment as they proved consistently superior or inferior in the early stages of the experiment or they were unavailable. Also, not all locations were included each year due to non-availability of acreage. The data indicate that there was a high degree of variability among cultivars and growers. They also indicate considerable variability among years of production although good cultivars were rated highest within seasons. Most notable was the variability among locations; the variation from one location to another was often as great as that among cultivars. Storage difference was pronounced as expected due to temperature regimes.     

The effect ofCorynebacterium sepedonicum on symptoms and yield of four potato cultivars

Summary Inoculating the roots of potato cvs Ostara, Laila, Kerrs Pink, and Pimpernel withCorynebacterium sepedonicum caused severe rotting of tubers and between 12 and 51 % decrease in yield. There was a significant cultivar/infection interaction. The numbers of tubers decreased significantly except for cv. Laila, which also showed little rotting of tubers, and the average tuber weight decreased most in cv. Pimpernel. The concentration ofC. sepedonicum was high in most inoculated tubers including those not showing symptoms.

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Zusammenfassung Wurzeln von gekeimten Saatknollen der Sorten Ostara, Laila, Kerrs Pink und Pimpernel wurden durch Tauchen in Suspensionen vonCorynebacterium sepedonicum inokuliert. Dies erbrachte einen betr?chtlichen und signifikanten Ertragsrückgang, vor allem bei der Sorte Pimpernel (Tabelle 1); desweiteren zeigte sich eine signifikante Sorte/Infektion-Wechselwirkung. Inokulation ergab, mit Ausnahme von Laila, eine signifikante Senkung der durchschnittlichen Knollenzahl (Tabelle 2); am gr?ssten war der Rückgang bei Kerrs Pink, w?hrend das durchschnittliche Knollengewicht am meisten zurückging bei Pimpernel (Tabelle 3). Der Ertragsrückgang bei Laila erfolgte durch Reduktion des durchschnittlichen Knollengewichtes, bei den anderen Sorten jedoch durch Rückgang der durchschnittlichen Knollenzahl. Diese Beobachtung l?sst darauf schliessen dass die Entwicklung der Infektion bei Laila nach der Knollen-Initiierung einsetzte, w?hrend sie bei den anderen Sorten schon früher einsetzte und somit die Knollenzahl beeinflusste. Im Gegensatz zu den anderen Sorten zeigten einige Tochterknollen von Laila ?ussere Symptome, in Verbindung mit starker F?ule, w?hrend in der Entwicklung interner Symptome nur geringe Unterschiede zwischen den Sorten gefunden wurden (Tabelle 4). Dennoch waren die Konzentrationen vonC. sepedonicum in den meisten symptomlosen Tochterknollen inokulierter Pflanzen hoch (Tabelle 4). Die Ergebnisse zeigen dass die Sorte Laila gegen eineC. sepedonicum-Infektion resistenter als die anderen geprüften Sorten ist, dass jedoch hohe Konzentrationen des Erregers in symptomlosen Knollen von inokulierten Pflanzen gegen eine Verwendung bei der Züchtung sprechen.

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Résumé Des racines de tubercules de semence germés (variétés Ostara, Laila, Kerrs Pink et Pimpernel) sont inoculées par immersion dans des suspensions deCorynebacterium sepedonicum. Cela provoque une diminution conéquente et significative du rendement, en particulier pour la variété Pimpernel (tableau 1), et il existe une interaction significative variété/infection. L'inoculation diminue significativement le nombre moyen de tubercules (tableau 2) sauf pour la variété Laila; la diminution est la plus importante pour la variété Kerrs Pink, tandis que le poids moyen de tubercules diminue le plus pour la variété Pimpernel (tableau 3). La diminution du rendement pour la variété Laila est provoquée par une réduction du poids de tubercules. Cette observation suggère que le développement de l'infection pour la variété Laila débute après l'initiation de tubérisation, alors que pour les autres variétés, elle commence plus t?t et de ce fait influence le nombre de tubercules. Peu de tubercules fils de la variété Laila montrent des sympt?mes externes associés à une pourriture importante en comparaison avec les autres variétés, alors que de petites différences s'observent entre toutes les variétés au niveau du développement de sympt?mes internes (tableau 4). Les concentrations deC. sepedonicum sont cependant élevées dans la plupart des tubercules fils ne présentant pas de sympt?mes et provenant de plantes inoculées (tableau 4). Les résultats montrent que la variété Laila est plus résistante à l'infection deC. sepedonicum que les autres variétés testées, mais les fortes concentrations du pathogène dans les tubercules sans sympt?me provenant de plantes inoculées empêchent son utilisation en multiplication.

     

Chemical vine desiccation of two potato cultivars

Russet Burbank and Onaway potato (Solanum tuberosum L.) vines were desiccated with diquat (6,7-dihydrodipyrido (1,2-a:2′1′-c) pyrazinediium ion), ametryn (N-ethyl-N-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), and endothall (7-oxabicyclo (2.2.1) heptane-2,3-dicarboxylic acid) applied at various rates alone or combined with surfactants, drift retardant, copper, or ammonium sulfate. Diquat and paraquat at 0.28 and 0.56 kg ha^?1 plus nonionic surfactant thoroughly desiccated Onaway and Russet Burbank potato vines. Only Onaway vines were thoroughly desiccated by ametryn at 1.3 and 2.3 kg ha^?1. Endothall at 0.87 kg ha^?1 provided thorough desiccation of Russet Burbank vines. The addition of a drift retardant did not reduce the effectiveness of diquat, while combining either ammonium or copper sulfate with diquat slowed the dieback of potato vines in 1987. Combining copper sulfate with diquat also slowed the dieback of Onaway vines in 1988. Both copper and ammonium sulfate, combined with diquat and nonionic surfactant, slowed the dieback of Russet Burbank vines when evaluated two days after application, but seven days later, no difference in vine dieback was evident. Crushing plants by rolling the field prior to desiccant application quickened vinekill by 18%. Applications of diquat using flat fan nozzles at 333 kPa provided vinekill equivalent to applications using hollow cone nozzles on a 25 cm spacing at 833 kPa, when spray volume for both applications was 467 L ha^?1. Potato yield, percentage of U.S. No. 1 potatoes, and stemend discoloration were unaffected by chemical desiccation.