Potato Stocks Research Articles

Virus content of seed potato stocks produced in a unique seed potato production scheme

SummaryWestern Australia has a unique seed potato production scheme which has remained virtually unchanged for more than 60 years, consisting of summer plantings of predominantly one cultivar in wind‐exposed coastal swamplands. No rotation is used and the scheme relies on natural winter flooding and ‘grazing’ by sheep to eliminate unharvested tubers. Stocks are recycled every year with only limited inputs of pathogen‐tested seed tubers in recent times. Virus spread in the crop is controlled by selecting large tubers for planting, roguing, aphicide application and growing season inspections. Potato viruses X and S were commonly detected in old seed stocks produced by this scheme attaining 100% infection in some. Both viruses were less frequently found in newly introduced seed stocks. By contrast, potato virus Y was never detected and potato leaf roll virus rarely found.

Variation in pathogenicity among field isolates of Phoma exigua var. foveata

SUMMARYExperiments carried out using a point inoculation method to infect potato tubers with Phoma exigua var. foveata demonstrated considerable variation in pathogenicity among field isolates. This variation was unlikely to be due to differential reductions in isolate pathogenicities during axenic culture. However, fresh field isolates generally produced larger lesions than stored isolates. An investigation of the distribution of pathogenicity variation in the fungus revealed that differences among isolates from different lesions taken from the same potato stock were greater than those between stocks, but pathogenicity variation within each lesion isolate was small relative to that between isolates. The importance of using isolates with a high level of pathogenicity, hence recent field isolates, in studies of this pathogen is stressed.

Occurrence of the Andean strain of potato virus S in imported potato material and its effects on potato cultivars

Infection with potato virus S Andean (PVSA) and ordinary (PVSo) strains was found in potato breeder's selection No. 8163‐511 imported from West Germany; the two PVS strains were differentiated by their reactions on Chenopodium quinoaTests on potato leaf samples using enzyme‐linked immunosorbent assay followed by inoculation to Cquinoa were subsequently used to detect PVSA and PVSo in a large‐scale survey of imported and domestic potato material. PVSA was detected in breeders' selections and cultivars imported from the Netherlands and West Germany, but not in domestic certified seed potato stocks or farmers' once‐grown stocks. PVSo was found in both imported and domestic certified stocks, but infection was commoner in the imported ones. When plants of C. quinoa, C. amaranticolor, C. murale and Nicotiana debneyi were inoculated with four isolates of PVSA, one induced mild symptoms while the reactions of the others ranged from moderate to severe. When plants of different potato cultivars were inoculated with three isolates, the plants were mostly infected without symptoms. However, when tubers from some were grown on, the progeny plants of most of the different combinations of cultivar and isolate of PVSA developed one or more of the following symptoms: vein deepening, rugosity, interveinal chlorosis, premature senescence and early loss of lower leaves.

Antiphytovirale Wirkungen von 1,5‐Diacetyl‐2,4‐dioxohexahydro‐1,3,5‐triazin (DA‐DHT)*

Abstract Antiphytoviral activities of 1,5‐diacetyl‐2,4‐dioxohexahydro‐1,3,5‐triazine Substitution of 2,4‐dioxohexahydro‐1,3,5‐triazine (DHT) by two acetyl groups resulted in an antiphytoviral compound, 1,5‐diacetyl‐2,4‐dioxohexahydro‐1,3,5‐triazine (DA‐DHT), which inhibits PVX, PVY, ToMV, TMV and TRV better than DHT, but only after, application at relatively high concentrations (10−2 mol/1). The antiphytoviral activity of DA‐DHT is enhanced by combined treatments with DHT as well as with cyanoguanidine, sodiumalkanemonosulfonate and 2‐anilino‐5‐adamantyl‐1,3,4‐thiadiazole., DA‐DHT reduced the number of symptoms of PLRV bearing potato eye cutting plants to a higher percentage than DHT. But the highest reduction was brought about by combined treatments with DA‐DHT, cyanoguanidine, sodiumalkanemonosulfonate and 2‐anilino‐5‐adamantyl‐1,3,5‐thiadiazole. Moreover, treatments with DA‐DHT increased more than treatments with DHT the mass of potato tubers produced by potato eye cutting plants. Combined treatments with DA‐DHT and the above mentioned substances reduced the natural infection with PLRV of a completely healthy potato stock for about 70 % and that of PVY for about 40 %. Thus, the DA‐DHT containing preparations may be capable of keeping potatoes in a good state of health even in regions with a high infection pressure.

Contamination of potatoes by Erwinia carotovora during grading

Considerable tuber contamination by soft rot erwinias in rotting tubers can occur when grading potato stocks. Erwinia carotovora pv. carotovora, from a single rotting tuber, contaminated c. 100 kg of potatoes during mechanical grading, c. 50% being contaminated with 104–105 bacteria per tuber. Survival of the bacteria during storage was related to the degree of damage sustained by the tubers during grading which in turn depended on the model of oscillating riddle grader used and the cultivar of potato. Chemical disinfection of the grader immediately before use and of tubers immediately after grading reduced contamination.

Soft rot Erwinia bacteria in the rhizosphere of weeds and crop plants in Colorado, United States and Scotland

The soft rot coliform bacteria Erwinia carotovora subsp. carotovora and E. carotovora subsp. atroseptica were isolated by an enrichment method from the rhizosphere of many weed species and crop plants, collected in commercial potato fields either currently in potatoes or in a different crop as part of the rotation. Erwinia carotovora was isolated from 24 plant species in Colorado and 47 species in Scotland. Weeds contaminated with E. carotovora were found in fields growing other crops in which potatoes had not been grown for 1–2 and sometimes much longer. Weeds collected from virgin land in Colorado were not contaminated with E. carotovora but in Scotland virgin soils containing weed roots yielded E. carotovora subsp. carotovora. In general, the numbers of contaminated weeds rose from nil or low levels in spring and early summer to considerably higher levels during mid‐season, and fell to progressively lower levels later. Erwinia carotovora subsp. carotovora was the predominant organism recovered from the rhizosphere, but E. carotovora subsp. atroseptica was less common, especially in Scotland, and its incidence varied in different seasons depending on factors such as temperature and moisture conditions. The bacteria could apparently persist in the root zone for an extended period of time and may be a source of inoculum to contaminate soft rot erwinia‐free seed potato stocks; the origin of the bacteria was uncertain.

Incidence of potato virus V in potato stocks in England and Wales

Incidence of potato virus V in potato stocks in England and Wales

Establishment and Multiplication of Virus‐free Nuclear Stocks of Potatoes in Denmark1

A programme of meristem‐stem tip culture of potato was initiated in Denmark in 1977 to eradicate Corynebacterium sepedonicum and at the same time produce virus‐free stocks. The procedures for obtaining the cultures, and ksting for viruses, at the National Institute of Plant Pathology are described. The first tuber generation is further propagated for 2 years by the Research Institute for Potatoes at Tylstrup. Selected growers then multiply the « meristem potatoes » under the pre‐basic system for another 3 years, under the supervision of the National Committee for Health Control of Seed Potatoes.

Occurrence of resistance‐breaking strains of potato virus X in potato stocks in England and Wales

Occurrence of resistance‐breaking strains of potato virus X in potato stocks in England and Wales

Comparison of nucleic acid hybridisation and other tests for detecting tobacco rattle virus in narcissus plants and potato tubers

SUMMARYAll isolates of tobacco rattle virus (TRV) found in naturally infected narcissus leaves produced nucleoprotein particles, mostly in large concentrations but, because of antigenic diversity, less than half of the isolates were identified by immunosorbent electron microscopy (ISEM) and still fewer by enzyme‐linked immunosorbent assay. All were identified by a nucleic acid hybridisation test in which DNA complementary to RNA‐1 of strain PRN of TRV was allowed to react with nucleic acid extracted from leaf tissue.Spraing‐affected tubers in some potato stocks yielded only NM isolates of TRV. These isolates do not produce virus particles and they were therefore not detected by ISEM. The infectivity of nucleic acid extracts from recently harvested tubers with spraing symptoms was much greater than that of extracts prepared from tubers after 8 months' storage. In other potato stocks, some spraing‐affected tubers contained NM isolates and the rest contained particle‐producing isolates (M isolates) of TRV. The infectivity of sap and of nucleic acid, extracted 7 months after harvest from tubers infected with M isolates, was much greater than that of nucleic acid extracted from comparable tubers infected with NM isolates. TRV was detected by nucleic acid hybridisation in extracts of almost all tubers containing either M or NM isolates, even when the tubers were not tested until 7–8 months after harvest. The probable sequence of events occurring after tubers are infected with TRV is outlined, and it is suggested that the virus will rarely become established in fields as a result of planting infected tubers.

Contamination of pathogen-free seed potato stocks byErwinia carotovora during multiplication: Results of a six-year monitoring study

Recontamination byErwinia carotovora of seed potato stocks (VT) derived from stem cuttings in the process of multiplication was monitored on four farms in the east of Scotland from 1973 to 1978. Randomly selected VT stocks of different ages from a wider range of farms were also examined. The results showed that although contamination can occur early during stock multiplication there was, in general, no stepwise increase in contamination level from one generation to the next. However, contamination tended to be greater after the third multiplication year when stocks are grown by conventional methods used for lower-grade seed stocks. It is notable that contamination was consistently high on some farms and low on others. Contamination byE. carotovora var.carotovora tended to be greater than byE. carotovora var.atroseptica. These results may be explained by the farm practices of individual growers, soil moisture status and aerial transmission of the bacteria. The results also indicate that contamination of some potato stocks derived from stem cutting could be maintained at a low level over several generations more readily on some farms than on others.

Soft Rot Erwinia Bacteria in the Atmospheric Bacterial Aerosol

Using a Casella High Volume Airborne Bacteria Sampler, the soft rot coliform bacteria Erwinia carotovora var. carotovora and E. carotovora var. atroseptica were caught from the open air during rainfall in mid to late summer, autumn and early winter, but not in late winter, spring or early summer. They were not found every time it rained, and never when the weather was dry. The bacteria were caught close to potato crops, but there were several occasions when they were found at sites where there were no such crops or at times of year after potato crops had been harvested. The sources of the organisms are uncertain, but those obtained close to potato crops may have originated there. The results are considered to provide further evidence that airborne spread and subsequent deposition of viable bacteria could cause contamination of Erwinia‐free potato stocks, and suggest that rainfall is a major generator of the general atmospheric bacterial aerosol.

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

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

Quantitative Studies on the Generation of Aerosols of Erwinia carotovora var. atroseptica by Simulated Raindrop Impaction on Blackleg‐infected Potato Stems

Quantitative studies on the generation of bacterial aerosols by simulated raindrop impaction on potato stems infected with the blackleg organism Erwinia carotovora var. atrosep:ica have shown that, theoretically, airborne transmission might result in re‐contamination of blackleg‐free potato stocks.

Waste potato dumps as sources of insects contaminated with soft rot coliform bacteria in relation to re-contamination of pathogen-free potato stocks

Insects belonging to 12 genera in the Order Diptera, found at two large waste potato dumps in Scotland. were contaminated with soft rot coliform bacteria. In 1973, 5.7% and 3.2% and in 1974, 4.8% and 4.1% of the insects caught at each site yielded these organisms. The bacteria were identified mainly asErwinia carotovora var.carotovora, though some isolates wereErwinia carotovora var.atroseptica. Isolations from potato dump waste showed that at the time when fly activity was greatest the majority of soft rot coliforms in the waste wereE. carotovora var.carotovora, despite the fact that tubers originally forming the dumps were almost certainly infected mostly withE. carotovora var.atroseptica. Contaminated insects could readily transmit soft rot coliforms to damaged areas on the aerial parts of potato plants. It is suggested that potato stocks freed from these organisms by the stem cutting procedure could become re-contaminated by insects that disperse from potato dumps.

The Storage of Potatoes and the Maine Potatoes Futures Market

The relationship between the storage of potatoes and the carrying charges reflected on the futures market for Maine potatoes gives rise to a situation in which the observed facts do not seem to agree with the accepted theory. The theory regarding intertemporal price relationships based on the work of Brennan, Telser, and Working establishes that the difference between the current price and the expected price of a storable commodity must be equal to the marginal cost of storage minus the convenience yield. The relationship between the amount of a commodity held in storage and the equality of the marginal cost of storage with the temporal price spread gives rise to a supply of storage curve. As estimated by Brennan, Telser, and Working, this supply of storage curve slopes upward to the right. More storage will be supplied at a high return per unit and less storage at a low return per unit stored. The carrying charges reflected on the Maine potatoes futures market seemingly contradict the theory of the price of storage in two respects. First, the spreads between futures, which establish a return to storage, sometimes appear to greatly exceed any typically plausible cost of storage. On 1 March 1976, the March future for Maine potatoes sold for $8.35 per hundredweight, whereas the May future was selling for $12.63 per hundredweight. The return to storing potatoes for two months was $4.28 per hundredweight. Second, the relationship between the level of potato stocks and the carrying charge appears to be the opposite of that previously estimated for commodities with continuous inventories. For potatoes, the seasonal pattern associates large stocks with a narrow carrying charge and small stocks with a wide carrying charge. The level of potato inventories and the spread on the futures market produce a relationship that slopes downward to the right. The fall potato crop accounts for over 75% of annual U.S. production and in recent years has been about 84% of the total. Fall crop potatoes are stored for consumption over a sevenor eight-month period. However, potatoes cannot be effectively stored for a whole year, since they are semiperishable. Potatoes, therefore, give rise to a discontinuous inventory situation. The task of intertemporal allocation is more difficult for a discontinuous inventory commodity. Potato prices must be established during the storage season with the objective of exhausting the supply of potatoes in storage coincidently with the availability of spring and early summer potatoes (Gray). Potato storage is conducted not by merchandising or storage specialists but primarily by growers. The primary requirements of a potato storage facility are adequate insulation, ventilation, and heating and the means to enter and remove the tubers efficiently.

Propagation of Pathogen‐free Potato Stocks by Stem Cuttings within a Clonal Selection Program1

ABSTRACTClonal selection with associated clinical tests and based on stem cuttings as the initial propagative material has been successfully adopted as a method of producing nuclear stocks of potato varieties free from certain important viruses, fungi and bacteria. The maintenance of health of such nuclear material during the subsequent period of multiplication to commercial quantities, however, has emphasized that gaps in our knowledge of the epidemiology of the diseases caused by these organisms exist and require investigation, so that clonal selection programs can make a maximum contribution to crop improvement.La sélection clonale assortie de tests cliniques, basés sur le bouturage par prélèvement sur tiges pour le matériel initial de reproduction, a été adoptée avec succès pour la production de stocks nucléaires de variétés de pommes de terre indemnes de certains virus, champignons et battéries importants. Les difficultés rencontrées dans le maintien d'une qualité sanitaire élevée de ce matériel nucléaire, pendant la phase de multiplication précédant la commercialisation, ont révélé les lacunes qui subsistent dans la connaissance épidémiologique des différents organismes pathogènes en cause.

Re‐infection by Erwinia carotovora (Jones) Bergey et al. in Potato Stocks derived from Stem Cuttings1

ABSTRACTPropagation of potato stocks by the stem cutting method has produced crops almost entirely free from infection with the soft rot coliform bacteria, Erwinia carotovora (Jones) Bergey et al var. atroseptica (Hellmers et Dowson) Dye and E. carotovora var. carotovora Dye. However, low levels of re‐infection have occurred and evidence indicates that a source of the organisms was infected insects. Air‐borne spread of bacterial aerosols generated by raindrop impaction on infected stems might also result in healthy stocks becoming re‐infected.

Contamination byErwinia carotovora of seed potato stocks of stem cutting origin in the process of multiplication

Surveys were done in the winters of 1973–4 and 1974–5 of 75 and 78 Scottish potato stocks, respectively, derived from stem cuttings. The results showed that these VTSC stocks were contaminated byErwinia carotovora early in their bulking, most being contaminated, often extensively, by the fifth year of multiplication. Especially in the early years of multiplication, the proportion ofE. carotovora var.carotovora toE. carotovora var.atroseptica was greater than that previously found in commercial stocks not derived from stem cuttings. Contamination levels in VTSC stocks were lower in the north than in the south, and in 1974–5 than in 1973–4. These differences were tentatively explained in terms of higher soil moisture deficits in the north in both years and in all regions in 1974 at a time during the growing season when the bacteria spread from the rotting mother tuber to the daughter tubers.

Recurrence of soft rot coliform bacterial infections in potato stem cuttings: an epidemiological study on the central nuclear stock production farm in Scotland 1967–74

Propagation of potato stocks from stem cuttings has produced material almost entirely free from infection withErwinia carotovora var.carotovora andE. carotovora var.atroseptica: during 1967–74, very few infected plants or tubers were found on the nuclear stock farm. When infection occurred,E. carotovora var.carotovora was the organism most often isolated, whereas in ordinary commercial stocksE. cartotovora var.atroseptica predominates. In 1973 and 1974 dipterous insects caught at a nearby dump of decomposing vegetable matter were contaminated withE. carotovora var.carotovora several weeks before infection was found on potato stems. Serotypes ofE. carotovora var.carotovora isolated from insects and infected plants were very often identical, providing compelling evidence that the source of the organisms was the dump, from which contaminated insects dispersed and subsequently transferred organisms to the crop. The origin of infections withE. carotovora var.atroseptica remains unknown.