Tensile properties of potato tubers

Mechanical properties of Kennebec and Russet Burbank potato tubers were computed from Force-elongation data on specimens cut from the tuber and tested in tension. Specimens cut from three locations in fresh and stored tubers were tested at varying strain rates at 70 F (21 C) and at 42 F (6 C). Results were analyzed for significant differences. Tests were conducted in 1964 and 1966. In spite of some differences in tuber condition and test and analysis methods, there was good agreement of results between the years. Mean values of properties for all tests were: tensile strength, 98 psi; strain at failure, 0.193 in./in.; and failure modulus (stiffness), 727 psi. Properties varied greatly with location in the tuber. The pith, in the center, is stronger and stiffer than the perimedullary zone surrounding it, and the skin-cortex exhibits different properties than either of these two. Storage affected properties at the skin and in the center much more than in the perimedullary zone. As strain rate increased, tensile strength and stiffness generally increased, and strain at failure decreased. Stiffness generally increased when temperature decreased. Effect of variety was mixed. One of the greatest problems in designing and using potato handling and processing equipment is damage to the potatoes. This lowers their market value and increases their susceptibility to disease and deterioration in storage. Various investigators, by dropping or hitting tubers experimentally or by following them through normal hanlling operations, have determined the external causes of damage to whole tubers and conditions that promote it. These experiments have yielded much needed information, but they tell little about the properties of th tubers that make them so susceptible to injury. Finney (2) and Timbers (7) have attempted to determine some of the mechanical properties of potato tubers and report them in engineering terms. This type of approach is necessary for an understanding of the behavior of potatoes in handling and processing operations. The purpose of this study is to determine mechanical properties of potato tuber tissue and report them in terms that will be usable by people who do further work in this area. Because at least some cracks in potatoes are caused by failure in tension, and because no record of tests on potato tissue in tension was found, these tests were conducted on specimens of potato tuber in tension.     

Relationships Between Internal Brown Spot and Skin Roughness in Potato Tubers Under Field Conditions

Internal brown spot (IBS) is a physiological disorder of potato tubers consisting in the appearance of punctiform and/or enlarged rust-coloured necrosis in parenchymal tissues. The IBS disorder leads to important economic impact and yield depreciation since quality, sensory and processing features of tubers may be highly compromised. Nowadays, the causes of IBS are still debated; however, the combination of several genetic, nutritional and environmental factors seems to have a relevant role in modulation of symptoms. In the current work, IBS occurrences together with skin roughness were monitored in potato tubers of different cultivars harvested in 2 years of field trials under different field conditions (environment, irrigation rate). All three IBS-susceptible cultivars used, Luminella, Majestic and Ricciona di Napoli, showed significant IBS incidence. Importantly, incidence and severity increased with tuber size. Ricciona di Napoli was the cultivar most affected by both IBS and skin roughness. Findings showed a strong positive correlation between IBS and skin roughness, suggesting that suboptimal growth conditions may have affected both physiological disorders. The association between IBS and potato skin roughness may provide new insights for the implementation of non-destructive IBS detection in potatoes.     

Analysis of Yam Minisett technique adoption in Nigeria

White yam (Dioscorea rotundata Poir.) is an important tuber crop grown throughout West Africa, the Caribbean, and Latin America. Propagation of the crop is primarily vegetative, through the use of small whole tubers (seed yams) and cut pieces of tuber (setts) planted to produce the larger tubers (ware yams) that households consume and sell. The Yam Minisett Technique (YMT) was introduced in Nigeria in the late 1970s as a means of increasing the production of seed yams. The YMT is different from many other agricultural technologies in that it requires farmers to do something – cut their tubers into small pieces – which they feel based on experience is potentially damaging as it causes rot. Indeed, the existing literature suggests that adoption of the YMT tends to be low and variable. However, to date there has been no systematic analysis of the existing literature on YMT adoption designed to explore which factors are reported to be the most important and why. Hence, the objective of this paper is to analyze the YMT adoption studies published to date to explore which factors are particularly important, and how this may help guide future research in YMT adoption. The results suggest that uncertainty – risk and ambiguity aversion – as perceived by farmers is a key consideration in YMT adoption and needs to be considered in future work.     

Drycore Appears to Result from an Interaction between Rhizoctonia solani and Wireworm (Agriotes ssp.)—Evidence from a 3-Year Field Survey

Drycore is an important quality deficiency in Europe especially in organic potato production and after grass clover leys. The drycore symptom is attributed to Rhizoctonia solani Kühn (teleomorph: Thanatephorus cucumeris (Frank) Donk). In the framework of a 3-year survey (2001–2003), data concerning potato quality, crop rotation, management, and site parameters were analysed from 185 potato fields. The hypothesis was tested that injuries on potatoes caused by wireworms facilitate the penetration of R. solani and favour the formation of drycore. Analysis of variance showed a significant influence of wireworm damage, seed quality, and grass clover leys in the crop on the level of drycore damage. On fields which had both a low occurrence of black scurf on the seed tubers and a low occurrence of wireworm damage at harvest, significant drycore damage was never observed. The relative risk for drycore damage on tubers was significantly higher if black scurf or wireworm damage was on the same tuber. In contrast, no higher risk for drycore was observed on tubers with slug damage. Abiotic factors like farm manure application, organic matter content, texture, and pH of the soil also had no significant influence on the level of drycore. Thus, the wounding of potatoes by wireworm could be confirmed as the major variable for drycore. The mode of action has to be clarified under controlled conditions.     

Determination of the potential for development of bacterial soft rot of potatoes

A method has been devised for assessing the potential hazard of soft rot development in potatoes. Tubers are placed in a mist chamber at 20 C (68F), a film of water is maintained on the tuber, and the extent of decay is assessed after 5 days. The soft rot potential determined in this way is intended as apractical indication of potential storage hazard, reflecting the overall effect of the various factors leading to bacterial decay. Tubers that had passed through a flume system and a rinsing spray in a commercial packing plant had a greater decay potential, even after passage through a hot-air dryer, than unwashed tubers. Differences in decay potential could be demonstrated between tubers that had been mechanically harvested and loaded into storage bins and those that had been harvested manually. In addition to the effect of mechanical damage and of passage through flumes, the decay potential was probably affected by the inoculum level ofErwinia carotovora. Pectolytic clostidia were also usually present in tubers rotting in mist chambers, and are probably involved in the decay.     

西南山区马铃薯病虫害状况分析

西南山区由于其立体气候的多样性而使马铃薯发生多种病虫害,造成产量的不稳定性。通过一系列的问卷调查和大田观察取样以及实验室病理检测,结果说明晚疫病、病毒病和青枯病是本地区最重要的病害。晚疫病常年造成１０％～３０％的产量损失,且每隔数年有一次大流行而造成更大的产量损失。种薯因病毒和其它病菌感染而不同程度地影响到产量的发挥。青枯病的发病规律较为复杂且较难预测控制。这几种病害的发生程度与作物生长季节、海拔、种薯年龄、品种、农艺措施等等密切相关。现有品种间发现有抗晚疫病和青枯病的差异。土样根系样中发现有各种寄生性线虫存在,但其危害性特别是与青枯病的关系有待进一步研究明确。２８星瓢虫是本地区危害最重的害虫。本文还列举讨论了各种病虫害防治措施。     

Short-Term exposure to low temperature in the fall affects field performance of seed tubers

Field trials were conducted in Alberta and Ontario with Norchip, Norland, Russet Burbank, Sangre and Superior potato cultivars to determine response to short-term exposure of seed tubers to below freezing temperatures in the fall. Exposure of the dormant seed tubers to ?-1 C for up to 48 hours did not affect the yield or growth characteristics of the cultivars. However exposure of seed tubers to ?-5 C temperatures for 6 or 12 hours caused marked (P < 0.05) reductions in marketable yield, marketable tuber number, maturity and vine size. Exposure to ?-5 C for periods longer than 12 hours resulted in severe freezing damage and subsequent decay of most of the tubers.     

Studies on natural repellents against potato tuber moth (Phthorimaea operculella Zeller) in country stores

Summary The effects of the leaves of five plant species, one from each of the generaAmbrosia, Anemone, Eupatorium, Eucalyptus andLantana, on potato tuber moth were investigated under indigenous storage conditions at the Central Potato Research Station, Shillong (1800 m above sea level). Their action was compared with that of a biological insecticide (spores ofBacillus thuringiensis), a chemical insecticide (carbaryl), and an untreated control. The data collected after six months storage on tuber damage, sprout damage and the rotting indicated that the leaves ofLantana aculeata provided most protection to the tubers, reducing damage from over 70% in the check to below 5%, and sprout damage from over 45% to below 3%. Next best wasEucalyptus globulus followed byB. thuringiensis. They may be used on tubers stored for table use or for seed as they had no adverse effect on germination or on the yield of a subsequent crop.     

Observations on the bulking and development of tuber size distribution in maincrop potatoes at Rothamsted in 1964–75

Summary Tuber samples taken at 2-week intervals from plots of cvs King Edward, Majestic and Pentland Crown in 1964–75 showed that the maximum bulking rates ranged from 1 to 5 tonnes/hectare/week. Maximum tuber numbers were usually produced by 11 weeks after planting and thereafter numbers declined. In September, about 70% of the tubers initiated were recovered, and between 24 and 52% of the tubers had reached marketable size (>4 cm). Tuber size distributions developed similarly in all years with all cultivars. During tuber initiation the distributions appeared as one population, and usually between 9 and 11 weeks after planting a second population of larger tubers developed. The population of small tubers later declined although in most years it was still present in September. This development fitted a model based on a mixture of two normal distributions and was determined by five parameters; the proportion of tubers in the small population and the means and standard errors of both populations.     

Quality assessment of antishock systems for potatoes

Summary Loading trailers and trucks includes a high risk for mechanical damage to potatoes, particularly when no anti-shock system is used. Manufacturers offer anti-shock equipment to reduce mechanical damage. A selection of anti-shock systems was compared. Firstly, the effect of protecting the product layer at the bottom of the trailer was investigated by dropping tubers in the empty trailer and analysing tissue discolouration and cracks. The combination of a shock absorber and a mattress yielded the highest bruise protection. Secondly, to investigate the bruising profile in the trailer and the damage reduction effect of each anti-shock system a bulk mass of potatoes was dumped into the trailer. Five hundred test potatoes were mixed into the bulk mass. Test potatoes were visually analysed for bruising and compared with controls (anti-shock systems absent). The results allowed the introduction of a mathematical relationship between drop height and tissue discolouration. Using an anti-shock system bruising was reduced by 10–90%, depending on the system and the bulk layer. On-field experiments were carried out to validate laboratory results. However site-specific harvest conditions and variable commodity properties made comparisons difficult.     

The effects of (S)-(+)-carvone treatments on seed potato tuber dormancy and sprouting

Summary Potato seed tubers may suffer from premature sprouting during storage, thus limiting their suitability for cultivation. Commonly used sprout suppressant treatments negatively affect but viability and therefore a reliable method to inhibit bud development must still be found for seed tubers. The monoterpene carvone ((S)-(+)-carvone) was tested in small scale experiments. The vapour of this compound fully inhibited bud growth of tubers cv. Monalisa stored at 23°C without affecting bud viability throughout 6 months of treatment. The most effective range of carvone vapour concentrations was between 0.34 and 1.06 μmol mol⁻¹. With these qualities we can expect carvone to become a suitable sprout suppressant for seed tubers.     

Reduction of potato damage during grading by radiant heating

Summary The effect of using radiant heat to quickly warm potatoes and reduce damage in handling after cold storage was investigated. Two treatments were investigated: tubers dropped 350 mm with no radiant heat applied, and tubers dropped with radiant heat applied. Both treatments were compared with a control set of tubers which were taken directly out of store. The mean damage index per tuber was significantly reduced following radiant heat treatment although there were cultivar and size variations. The temperature profile under radiant heat was also measured which showed an increase in the outside flesh temperature of 8–12°C depending on tuber colour.     

Field harvest damage affects potato tuber respiration and sugar content

Field and laboratory experiments demonstrate that damage to potato tubers increased tuber respiration, which declined with time. Measurement of tuber respiration with an infra-red gas analyzer can be a sensitive indicator of amount of tuber damage in actual field harvests. Damage of tubers had no effect on total sugar content but decreased sucrose content when measured ten days after harvest.     

Intercellular spaces enhance potato tuber elasticity

Summary The intercellular volume within tuber tissue increases with tuber maturation. At the same time, both tuber injury after mechanical load and lentical perforation after water uptake by tubers in wet peat decreases. The degree of tuber injury is correlated with intercellular space (r=−0.667,n=16) and with water saturation of tissue (r=0.697,n=16). The tubers lose water during storage. In wet soil wilted tubers take up significantly higher amounts of water than turgid tubers, and lenticel perforation is much more frequent. Tuber maturation in autumn and low water loss during storage enhance the cushioning effect of the intercellular gas volume of tuber tissue against outside mechanical load and internal tension after water uptake.     

Seminole: A new variety of potato combining good chipping characteristics with good field performance in Alabama,Florida, and North Carolina

Seminole (FL282 or B4469-7) is a new potato variety, named and released by the Research and Farm Departments of Frito-Lay, Inc. Its medium-early tubers are round to oblong with smooth, light cream-buff skin color. The eyes are shallow and pink. It was selected on the Research Farm, Rhinelander, Wisconsin from family line B4469, one of 399 family lines received from the National Potato Breeding Program, Beltsville, Maryland. Tested for its reaction to Verticillium wilt, it was one of the most resistant among 1,190 seedlings. It proved superior to many named and numbered varieties in specific gravity and chip color. In Alabama, Seminole produced relatively high yields of tubers with unusually high specific gravity. Tests in Florida and North Carolina gave similar results. In the South, Seminole is usually 7–10 days earlier than Sebago, and produces higher yields of tubers with higher specific gravity. Unlike Sebago, its tubers separate readily from the vines preventing losses in mechanical harvesting.     

Dynamic mechanical properties of the Russet Burbank potato as related to temperature and bruise susceptibility

An electro-mechanical vibration exciter and a dropped weight impact device were utilized to determine changes in dynamic mechanical properties of the Russet Burbank potato as influenced by temperature. The vibration exciter was utilized to study the compressive stress-strain relationship for core samples of tuberin the frequency range of 50 to 300 Hz and for temperatures from 35 to 85°F (2 to 30°C) Complex dynamic modulus, storage modulus, and phase angle were found to be independent of temperature but increased with frequency in the interval 50 to 300 Hz. Significant differences in the dynamic mechanical properties of tuber flesh were found according to location along the tuber where the samples were selected. In this study, the complex dynamic modulus was lower for the stem end than for the bud end of the tuber as was the bruise susceptibility Susceptibility of the tubers to bruise damage was evaluated by impacting the tubers with a dropped weight. Depth of bruise was found to be equivalent to length, width, area, or volume of bruise for determining bruise susceptibility. When the velocity of approach of the weight was considered, the ability to predict changes in bruise susceptibility was doubled over that of using temperature alone. This is an improtant finding because it may account for some of the unexplained variations in results of some previous studies where the impact device has been used The response of the Russet Burbank potato to impact was determined by placing a piezoelectric accelerometer in a falling weight. The acceleration-time history of the impact was recorded on a storage oscilloscope. Impact parameters were highly dependent on height of drop. Results of numerical integration of the acceleration-time curves are presented. Peak deformation was found to occur after the point of peak acceleration. Discontinuities in the acceleration-time traces were good indicators of severe damage     

Effects of spraying mefluidide onto potato foliage

Summary Spraying the growth regulator mefluidide onto potato foliage at 500 or 1000 g/ha on two dates in July after tubers had been initiated did not affect the number, size and yield of tubers or the extent of injuries after mechanical harvesting. The skin of some tubers from sprayed plants was brown and this was more common from plants sprayed on 15 July than on those sprayed two weeks earlier. Spraying at 1000 g/ha decreased the severity of black scurf but increased gangrene.     

Amylase Analysis in Potato Starch Degradation During Cold Storage and Sprouting

As the fourth most important food crop, potato plays a key role in food safety and economic development of the world. Harvested potato tubers can be stored for a long time, but sprouting and cold-induced sweetening (CIS) can seriously affect the quality of tubers during storage. One of the key pathways involved in CIS is starch degradation, in which both α-amylase and β-amylase play important roles. However, each amylase belongs to an extensive gene family and it is not clear which genes are the key regulators. In this study, we identified genes most likely regulating starch degradation. We first selected candidate genes from the public potato genome database and then investigated their expression patterns associated with reducing sugars and amylase activities. The results showed that the activity of α-amylase was mainly caused by StAmy23 and the activity of β-amylase was mainly caused by StBAM1 and StBAM7. In addition, α-amylase and β-amylase may play important roles in starch degradation of the tubers stored at low temperature and during sprouting, and the amylase activity may be regulated by the amylase inhibitor in cold-stored tubers.     

Methamidophos,Salithion, phenthoate,and R&H 0994 for control ofMyzus persicae(Sulzer) on tubers in Peru

The efficacy of methamidophos, Salithion, phenthoate, and R&H 0994 for control ofMyzus persicae (Sulzer) on stored tubers was determined. In Huancayo, Peru, which is in the Sierra, R&H 0994 proved to be most efficacious and protected tubers for 45 days. Phenthoate, at the rate tested, was not effective. In San Ramon, Peru, which is tropical in climate, methamidophos was most efficacious and protected tubers for 22 days. In both locationsM. persicae populations developed very rapidly on unsprayed tubers in rustic store.     

马铃薯试管薯诱导因子最佳组配的研究

应用多元分析方法研究马铃薯的诱导因子,得到薯块数(y_1)、薯块重(y_2),2个国标函数分别与光照强度(x_1)、CCC浓度(x_2)和BAP浓度(x_3)三项因素的回归数学模型。3个因素对于目标函数的影响程度不同,其中以光照强度的强弱影响作用最大,BAP和CCC浓度略次之。通过计算机摸拟筛选,得出最优组配为:黑暗条件下,MS+500～700 ppm CCC+3～5 ppm BAP。