Effect of rate and time of fertilization on nitrogen and yield of Russet Burbank potatoes under center pivot irrigation

Applying less N on Russet Burbank potatoes (Solanum tuberosum L.) at planting time may reduce the potential loss of N from sandy soil by wind erosion and leaching early in the season. The objective of this study was to evaluate the effect of rate and time of N fertilization on potato production. Potatoes were grown in outdoor pot cultures with N rates of 75,150 and 300 ppm and in field plots with N rates from 112 to 448 kg N/ha applied in single and split applications. The results from pot cultures harvested after one month’s growth showed that yield of tops increased and tuber yield decreased as applied N at planting increased from 75 ppm to 150 or 300 ppm. Field results showed that the yield of potatoes was as high or higher when N applications were split between planting and when plants were 15 to 20 cm tall (early tuberization) as with the same amount of N applied at planting. Generally 112 kg N/ha at planting time was sufficient when additional N was applied after emergence. Split application of N resulted in more second growth on tubers than when all of the N was applied at planting.     

Study of hydrogen peroxide,potato enzymes and blackspot

The rate of oxidation of tyrosine, p-cresol and catechol by potato enzyme diminished as H₂O₂ concentration increased. By contrast, the rate of oxidation of chlorogenic acid in the presence of H₂O₂ increased. Bovine catalase destroyed H₂O₂ and thus effectively prevented either H₂O₂-induced inhibition or acceleration of oxidation of the four substrates by potato enzyme. Horseradish peroxidase in the presence of H₂O₂ did not oxidize either monophenol, but oxidized both polyphenols. Possible association of H₂O₂, peroxidase and catalase with blackspot susceptibility is discussed.     

Blackspot of Russet Burbank potatoes and the carbon dioxide content of soil and tubers

These studies were designed to elucidate the influence of CO₂ on blackspot susceptibility of Russet Burbank potatoes. The influence of tuber CO₂ environment on blackspot was tested. Tubers from 1–4 and 6–8 inches deep in the soil were scored for blackspot and moisture samples were taken from their vicinity. Blackspot was worse in shallow tubers and in tubers from drier soil. Plowing under corn stover, covering the soil with plastic, and excessive irrigation failed to cause blackspot susceptible tubers. Diffusing CO₂ into the soil atmosphere under plastic sheets slightly increased the intensity of spot discoloration but the discoloration was atypical blackspot. Effects on blackspot by changing tuber gases was tested. Tubers whose gases had been evacuated and replaced by O₂, N₂, and CO₂ had lower blackspot scores than untreated tubers. Increasing the time tubers were soaked in water after gaseous evacuation reduced blackspot. Hydration consistently decreased tuber blackspot. In chemical studies, tubers were tested for blackspot and analyzed for CO₂ content. The relationship between tissue CO₂ and blackspot appeared to be inverse. Tuber CO₂ content was not influenced by time of day. Tuber blackspot scores immediately, 1, 3, and 7 hours after digging were the same, but tissue CO₂ content increased linearly with time after harvest.     

Cell wall thickness during growth of domestic and foreign potato cultivars

During growth of Russet Burbank tubers from less than 100 to over 250 g, thickness of parenchyma cell walls nearly doubled (1.9X) to slightly over 1 μ. Although affecting cell size at harvest maturity, different levels of N fertilizer and soil moisture had little influence on wall thickness. Wall thickness in Kennebec and Norchip increased to 0.9μ (1.7X), and in White Rose to slightly under 0.8 (1.2X). During the same growth, cell size nearly doubled in Russet Burbank. Cells of Kennebec, Norchip and White Rose averaged smaller than those of Russet Burbank at harvest maturity. Wall thickness and cell size showed similar relationships in foreign cultivars. Wall thickness in European varieties Bintje and Pimpernel was comparable to that of White Rose. Thickness in Atjimba closely approached that of Russet Burbank, and in Kamarz was similar to that of Norchip. Among South American cultivars, Doré had unusually thick walls (1.36μ), whereas those in Fruitella and Papa Bianca were between those of Norchip and White Rose. Bintje was comparable to domestic cultivars in tuber size, but all other foreign cultivars studied had medium to small tubers. Doré had unusually large cells for a small tuber. Differences in wall thickness may be due to differences in amounts of cell wall material, to differences in hydration properties of pectic components, or to combinations of both. Independently of wall thickness, the many primary pit fields in parenchyma walls may be a limiting factor in wall strength. The very thin pit membranes consist mainly of cellulosic microfibrils formed early in cell growth.     

Determination of disodium acid pyrophosphate in French-fried potatoes

An analysis procedure was developed to determine residual disodium acid pyrophosphate (SAPP) in French-fry strips after treatment. The uptake of SAPP in relation to concentrations and temperatures of the treating solution, lengths of treating time and loss of P₂O₇ from the finish-fried French fries are also considered.     

Anatomy and compositional variation within potatoes

Re-examination of the histological development of the potato tuber supports Artschwager’s view that tuber growth is predominantly due to enlargement of the perimedullary zone and is of procambial origin. Pith (medulla) and cortical regions are differentiated from the ground or fundamental meristem derived from the apical meristem of the stolon apex, even before tuberization has been initiated. The procambium gives rise to external phloem, primary xylem, internal phloem and associated parenchyma, and likewise to interfascicular parenchyma. Those parenchyma cells so formed inwardly to the xylem “ring” contribute to the growth of the perimedullary zone. The sequence of tissue origins is diagrammed and discussed from the viewpoint of modern concepts of histogenesis.     

Cell size in Russet Burbank potato tubers with various levels of nitrogen and soil moisture tensions

Russet Burbank potatoes were grown at levels of added nitrogen of 0, 135, and 270 kg/ha and soil moisture tensions (SMT) of 0.5 and 1.0 atm. With all combinations, there was a consistent gradient of larger to smaller starch-storage parenchyma cells from stem end to bud end of mature tubers. Stem and bud ends of tubers grown at a SMT of 0.5 atm with N had smaller cortical and pith (innermost medullary or water-core) cells than did ends of tubers grown without N. Perimedullary tissues of bud ends of tubers receiving N likewise contained smaller cells than did corresponding tissues of tubers grown without N. No pronounced differences in cell size were found in tissues from the midsections. In bud-end tissue of tubers grown at a SMT of 1.0 atm, there were no consistent differences in cell size with respect to N levels. However, pith, perimedullary, and cortical tissues of the midsections and stem ends of tubers receiving N had smaller cells than did corresponding tissues from tubers without N. The different patterns of cell size in tubers grown at different SMT indicate that the effects of N may be influenced by soil moisure.     

Oil content of French fries as affected by blanch temperatures,fry temperatures and melting point of frying oils

The oil content of par-fried frozen French fries prepared by two methods, conventional and freeze-leached, was not affected by blanch temperatures when blanched for 15 minutes. Melting points of the frying oil did affect the oil content of par-fried French fries. The differences were variable and could not be explained by melting point alone. Blowing the potato strips with ambient air after the par-fry and cooling below the melting point of the frying oil had no effect on the oil content of the frozen product. Contrary to previous reports, the oil content of the French fries increased significantly as the par-frying temperature was increased from 160.0 to 185°C (320 to 365°F) with the greatest increase occurring between 171.1 and 185.0°C (340 and 365°F). The French fries par-fried 1 min at 171.1 and 185.0°C (340 and 365°F) were judged to have identical quality after finish frying 3 minutes at 185.0°C (365°F). A lower par-fry temperature or possibly a shorter par-fry time at the higher temperature would be an advantage to the processor who could use less oil and energy without adversely affecting the quality of the final consumable product.     

Molecular epidemiological studies of veterinary arboviral encephalitides

Recent studies using molecular genetic approaches have made important contributions to our understanding of the epidemiology of veterinary arboviral encephalitides. Viruses utilizing avian enzootic hosts, such as Western equine encephalitis virus (WEEV) and North American Eastern equine encephalitis virus (EEEV), evolve as relatively few, highly conserved genotypes that extend over wide geographic regions; viruses utilizing mammalian hosts with more limited dispersal evolve within multiple genotypes, each geographically restricted. Similar findings have been reported for Australian alphaviruses. This difference may be related to vertebrate host relationships and the relative mobility of mammals and avians. Whereas EEEV and Venezualan equine encephalitis virus (VEEV) utilize small mammalian hosts in the tropics, most WEEV genotypes probably utilize avian hosts in both North and South America. The ability of mobile, infected avian hosts to disperse alphaviruses may result in continual mixing of virus populations, and thus limit diversification. This high degree of genetic conservation is also exhibited by EEE and Highlands J viruses in North America, where passerine birds serve as amplifying hosts in enzootic transmission foci. Most equine arboviral pathogens, including EEEV, WEEV and Japanese encephalitis virus (JEV), occur in a naturally virulent enzootic state and require only appropriate ecological conditions to cause epizootics and epidemics. However, VEE epizootics apparently require genetic changes to convert avirulent enzootic strains into distinct epizootic serotypes. All of these arboviruses have the potential to cause severe disease of veterinary and human health importance, and further molecular epidemiological studies will undoubtedly improve our ability to understand and control future emergence.