The effect of timed water stress on quality,total solids and reducing sugar content of potatoes

Potato (Solanum tuberosum L.) solids and reducing sugars were examined before, just after, and two weeks after transient water stress to gain an understanding of tuber changes that occur directly associated with water stress. Russet Burbank and A082260-8 potatoes were grown on Owyhee silt loam at the Malheur Experiment Station, Ontario, Oregon. Potatoes were subjected to a single episode of transient water stress by omitting furrow irrigation in either late June, July, or in early August of 1988 and 1989 to examine variety differences in the short term effects of water stress on changes in solids and reducing sugars in tuber stem ends. Irrigation was managed to maintain soil water potential above -65 kPa at 20 cm depth during tuber initiation through bulking except during transient stress when the soil water potential reached -82 to -110 kPa. Tuber samples were taken from plots and minimally stressed check treatments before stress, at the peak of stress, two weeks after the transient stress period, and after harvest. Tubers were sectioned longitudinally and the percent solids and reducing sugars were determined for samples from the tuber stem end, center, and apical end. Longitudinal tuber strips were fried after harvest to determine fry color. Tuber stem-end fry color did not darken in A082260-8 potatoes subjected to water stress. The line A082260-8 had higher stem-end solids and lower stem-end reducing sugars than Russet Burbank. Neither variety responded to transient water stress or recovery from transient stress with an immediate increase in reducing sugars in any tuber part. Reducing sugars were elevated in harvested tubers, particularly in the stem-ends of Russet Burbank potatoes subjected to water stress. Increases in tuber reducing sugars related to transient water stress were not found during the stress period or immediately after stress, but were present in harvested tubers.     

Impact of early-season water deficits on Russet Burbank plant development,tuber yield and quality

Russet Burbank potatoes grown on Owyhee silt loam were subjected to early-season moisture stress by delaying initiation of furrow irrigation up to seven weeks after planting. A range of water stress treatments from 4 to 7 weeks after planting resulted in reduced plant size, tuber number and total tuber weight per plant 8 1/2 weeks after planting. Early-season water stress resulting from delayed irrigation onset was associated with improved tuber quality at harvest. Plants water stressed before tuber initiation had fewer tubers with dark stem-end fry colors, reduced percentage of US No. 2 potatoes, and increased percentage and size of US No. 1 potatoes. Increasing duration of soil water potential below -60 kPa early in the season was associated with declining total yield in 1985 but not in 1986. To obtain optimum yield and processing quality, the first irrigation should be no sooner than full plant emergence.     

Growth and preharvest stress and processing quality of potatoes

The quality factors influenced by stress conditions are: total dry matter or starch content and distribution of starch, sugar content, types of sugars and distribution, texture, mealiness, flesh color, tuber size and shape, and tuber defects such as growth cracks, and hollow heart. Early stress during growth can cause tubers to become pointed on the stem-end with low starch content and high reducing sugars. Uneven growth due to stress results in growth cracks, or hollow heart and malformed tubers. Varieties differ considerably as to susceptibility. Stress generally causes lower starch content in tubers which results in greater sugar accumulation in storage. Relative maturity is also influenced by stress during growth. Immature and over-mature tubers (from prematurely dead plants) accumulate greater amounts of sugar in storage than tubers properly matured. Stress can also cause poor texture of processed products, such as tough texture of French fries as well as lack of mealiness. Flavor and color of processed products can also be detrimentally influenced by stress.     

Sugar-end in Russet Burbank potatoes

Tissue selected from the stem- and bud-end of reconditioned tubers having sugar-end disorder was compared by color after frying and chemical composition to tissue removed from the two ends of tubers without sugar-end disorder taken directly from cold storage at 45 F, and after reconditioning 3 weeks at 70 F. Chemical analyses of selected tissue suggested that the dark finish-fry color at the stem-end of sugar-end tubers following reconditioning at 70 F was due to the inability of the physiological systems within the tissue to convert reducing sugars to starch and/or to use these sugars in the respiratory process. Of the components analyzed, only a high reducing sugar content was associated with a dark finish-fry color. Neither sucrose nor free amino acid content was associated with the sugar-end disorder. Extending the reconditioning period at 70 F for sugar-end tubers did not lower the reducing sugar content or the darkening of the stem-end tissue on frying.     

Storage temperature and maleic hydrazide effects on sprouting,sugars, and fry color of Shepody potatoes

The effect of low storage temperature (4 to 8 C) and maleic hydrazide (MH) treatment on sprouting, sucrose and reducing sugar (glucose and fructose) concentrations in tubers, and fry color-sugar relationships of Shepody were determined and compared to Russet Burbank. Sprouting of Shepody was delayed by 3 to 15 weeks when the temperature was lowered from 8 to 6 or 5 C, respectively. Shepody accumulated more sugars at all storage temperatures than Russet Burbank. The reducing sugars accumulated in Shepody at 5 and 6 C could be lowered to levels acceptable for processing for about 24 weeks after harvest by reconditioning at 18 C for at least two weeks. MH increased glucose in Shepody stored at 5 C compared to untreated tubers. Excessive sprouting (> 10 cm sprout length) of nonsprout inhibited Shepody occured late in storage with four weeks reconditioning. Although not statistically significant, MH tended to cause darker fry color per unit of reducing sugar in Shepody compared to tubers from untreated plants. Storage of Shepody tubers not treated with MH could be extended a few weeks by temperatures < 8 C only if there is precise control over temperature, sugars are closely monitored, and reconditioning is rapid to minimize sprouting.     

The development of translucent end tubers

A study was made to gain greater understanding of the development of translucent end tubers which caused problems for french fry processors duringthe processing season of 1971–72. Analysis of seven commercial and three experimental samples revealed a lower dry matter and higher reducing sugar content in the basal portion of the tubers. Normally Russet Burbank potatoes contain higher dry matter in the basal end. A study of dry matter changes during growth and development in 1971 and of moisture stressed potatoes in 1972 showed a reversal in dry matter content and an uneven distribution of reducing sugars, whereas the normally irrigated potatoes maintained a higher percentage of dry matter in the basal portion throughout. A decrease in pH of the tissue accompanied the loss of starch from the basal portion of moisture stressed potatoes. As postulated by other research workers, the loss of dry matter is attributed to initiation of active growth of the apical end, thereby utilizing carbohydrates from the basal end following a period of stress. Immaturity of tubers and storage at low temperatures immediately after harvest caused water stressed potatoes to develop increased numbers of translucent ends in storage.     

The Relationship Between Soil Temperature and Sugar Ends in Potato

Sugar ends is a serious defect in processed potatoes. Among the more important factors associated with the development of sugar ends are soil temperature and soil moisture, particularly during early tuber bulking. This 2-year study was designed to examine the effects of soil temperature on the development of sugar ends. Soil temperature was recorded in different zones (0–10 cm and 10–20 cm depths) of potato rows oriented in north–south and east–west directions. At harvest, tubers from four sections in each field were hand excavated from each quadrant of the hill. The rows were divided vertically through the center and horizontally at the 10-cm depth. Tubers from each quadrant were weighed and then evaluated for fry color after 3 months of storage. Temperature profiles within the different regions of the row showed considerable variation throughout the season. Row orientation had a slight effect on soil temperature, but soil depth appeared to be more important. The deeper portion of the row (below 10 cm) was generally cooler throughout the day. East and north facing portions of rows also tended to be cooler than the opposite side that was exposed to more solar radiation. The highest yields and highest incidence of tubers with sugar ends tended to be found in areas below 10 cm in depth. These results contradict the notion that soil temperature is the primary factor leading to development of sugar ends. Therefore, individual tuber growth rate and temperature exposure of the entire plant may be more important in causing the development of sugar ends than was previously thought.     

The influence of defoliation date and harvest interval on the quality of potatoes for french fry production

Summary Trials were carried out in 1984, 1985 and 1986 in which the effect of four dates of defoliation (0, +10, +20, +30 days) and three intervals to harvest (0, +10, +20 days) on yield, tuber size, dry matter, reducing sugar, fry test colour and finish fried sensory quality were examined for two cultivars (Pentland Dell, Maris Piper) on two sites (medium silt, peaty loam). Dry matter content and yield of tubers were influenced by all factors in the trial. Later dates of defoliation gave the lowest reducing sugar levels, palest fry colour, highest yield and dry matter content. Increasing the interval from defoliation to harvest reduced dry matter and raised yield. Significant year effects were obtained for dry matter and reducing sugar content.     

Relationship of potato tuber periderm resistance to plant water status

Potato (Solanum tuberosum L. cv. Russet Burbank) tuber periderm resistance to water loss was monitored during the harvest season. Periderm resistance of tubers from water-stressed plants was compared with tubers from unstressed plants throughout a six-week harvest period, in order to determine the effect of plant condition on tuber resistance to water loss. Tubers stored for ten days at 4°C immediately following harvest were also monitored to determine if storage enhanced periderm resistance and if any difference occurred between tubers from stressed vines compared with those from unstressed vines. During the harvest season, tuber resistance to water loss was positively correlated with plant water stress, as measured by leaf water potential and leaf diffusive resistance. Storage of tubers after harvest also caused an increase in periderm resistance. The commercial practice of vine killing, therefore, may have a positive effect on reducing weight loss in storage by enhancing the resistance of tuber periderm to water loss.     

株行距和施肥量对木薯产量及生长的影响

采用裂区试验设计方法,研究株行距和施肥量对华南5号木薯产量和生长的影响.结果表明:在本试验株行距和施肥量条件下,施肥量对木薯产量和生长的影响比株行距大.密植(0.6～0.8 m)有利于提高淀粉产量、鲜薯产量和鲜薯淀粉含量,以0.8m株行距最佳,而疏植(1.2～1.4m)有利于提高单株薯数、单株鲜薯重、单株鲜茎叶重、收获指数和茎径.施肥有利于提高淀粉产量、鲜薯产量、单株鲜薯重、单株鲜茎叶重、茎径、株高和单株薯数,但降低鲜薯淀粉含量和收获指数.丰产栽培技术要兼顾单位面积株数、单株鲜薯重和鲜薯淀粉含量.建议在土壤肥力差和少施肥时,用0.6 m株行距;土壤肥力中等且较高施肥时.采用0.8 m株行距;土壤肥力中上且优越水肥管理,采用1.0 m株行距.     

The processing potential of tubers of the cultivated potato,Solanum tuberosum L., after storage at low temperatures. 2. Sugar concentration

Summary Several clones from a potato breeding programme at the Scottish Crop Research Institute (SCRI) produced acceptable (pale) coloured fry products after five months' storage at 4°C. Chemical analysis of tuber samples taken at five-week intervals during storage at 4°C and 10°C gave a substantial variation in glucose, fructose and sucrose concentrations among the 22 clones examined. Several unnamed SCRI clones showed little accumulation of reducing sugars when stored at 4°C. In marked contrast, the cultivars Record and Pentland Dell, currently the most widely used cultivars for fry processing in the UK, accumulated far greater levels of sugar during low temperature storage. Glucose concentration proved more important than fructose concentration in determining fry colour. Clones with the lowest concentrations of glucose after storage at 4°C also showed lowest concentrations when stored at 10°C. These results are in agreement with previous reports on the predictive value of glucose levels at harvest, but this is the first identification of such low temperature, low sweetening variants in agronomically adapted clones of the cultivated tetraploid potato.     

Soil water stress and the growth and yield of potato plants grown from microtubers and conventional seed tubers

Tuber yields of potato plants grown from microtubers in fields are more variable than yields from conventional seed tubers (CT). One reason could be their higher susceptibility to water stress. This study clarified the effect of soil water stress from 1 month after emergence on the growth and yield of plants grown from conventional seed tubers and microtubers in fields. Microtubers (0.5–3 g) and conventional seed tubers (50 g) were grown in Hokkaido, Japan, over three field seasons. One month after emergence, poly-shelters were placed over the plots to prevent rainfall, and either irrigated (wet plot) or non-irrigated (dry plot) treatments were formed. At mid-flowering (about 50 days after emergence) leaf area index (LAI) in microtuber plants was decreased relatively more due to soil water stress than LAI in conventional seed tuber plants. However, at maximum shoot growth (about 80 days after emergence) both microtuber and conventional seed tuber plants had a similar relative decrease in LAI due to soil water stress. At mid-flowering and maximum shoot growth microtuber and conventional seed tuber plants had reduced stomatal conductance due to soil water stress, but the reduction in stomatal conductance was greater in conventional seed tuber plants than in microtuber plants. Microtuber and conventional seed tuber plants had similar root development at maximum shoot growth. Tuber production from mid-flowering until plant maturity was similarly affected by soil water stress in microtuber and conventional seed tuber plants. At harvest, plants affected by soil water stress had about 87% of the tuber dry weight of irrigated plants. We conclude, that the greater variation on tuber yield of microtuber plants cannot be attributed to soil water stress from 1 month after emergence.     

Effect of seed source, presprouting and desiccation date on the processing quality of potato tubers for French fry production

Summary The effects of seed source, presprouting and desiccation date on processing quality parameters in the cultivars, Maris Piper and Rooster were investigated over four seasons. Tuber dry matter, sucrose, reducing sugar concentrations and fry colour were measured. Seed source did not affect sucrose concentrations, significantly affected tuber dry matter in three of the four seasons and had no effect on reducing sugar concentrations or fry colour. Presprouting seed, reduced sucrose concentrations during two seasons from four and increased dry matter concentration of cv. Maris Piper during one season from four and in cv. Rooster during two seasons from four; lowered reducing sugar concentrations following storage in one season from three and did not affect fry colour. Delaying the desiccation date decreased sucrose concentration in all seasons, increased tuber dry matter concentration during two seasons and induced higher reducing sugar concentrations and darker fry colours.     

Effect of soil water tension and harvest time on levels of infestation byPhoma foveata Foister in soil and on tubers and stems of potato (Solanum tuberosum L.) in northern Sweden

Summary The incidence ofP. foveata in soil and tuber samples from field experiments often increased significantly as the harvest season progressed and temperatures fell. Mean levels of tuber and soil infestation were significantly higher in irrigated rows compared with those artificially sheltered from precipitation, both at normal and late harvest dates. Soil infestation was most frequently detected within 10 cm of the parent tuber. No pycnidia were visible on the haulm, and very few latently infected stem segments and leaves were detected using various methods. In three out of four years, the incidence ofP. foveata in tubers after wounding was reduced by washing them gently in tap water immediately after harvest.     

The role of stem inoculum in the transmission ofFusarium sulphureum to potato tubers

Summary Over 2 years, seed tubers or stems were inoculated withFusarium sulphureum Schlecht. (F. sambucinum Fuckel f. 6 Wollenw.) and the incidence of dry rot on daughter tubers assessed by standardised wound tests. The amount of stem and soil inoculum was also measured in one year. Inoculating stem bases resulted in greater concentrations of spores on the stem bases, greater soil populations at harvest and more dry rot on tubers than inoculating the seed tuber. Overall, the incidence of dry rot and the amount of stem and soil inoculum was similar for the three methods of haulm destruction: cutting and removing the stems, applying sulphuric acid or applying diquat dibromide to the growing plants.     

Pomerelle Russet: an Early Maturing Potato Variety with High Yields of U.S. No. 1 Tubers Suitable for Fresh Market and mid-Storage Processing and Tolerance to Potato Mop-top Virus

Pomerelle Russet is an early maturing fresh potato variety, which produces moderately high early-season (95–110 days after planting) yields of long tubers with brown-russet skin. It is notable for its very attractive, smooth tubers and resistances to internal and external defects with a high percentage of U.S. No. 1 tubers. Fresh merit ratings for Pomerelle Russet in trials conducted in Idaho, Oregon and Washington were consistently higher than Russet Burbank and Russet Norkotah. Early harvest yields for Pomerelle Russet are generally comparable to Russet Norkotah with a higher percentage of U.S. No. 1 tubers. Compared to Russet Burbank and Russet Norkotah, Pomerelle Russet has greater resistance to Potato mop-top virus, soft rot, corky ringspot and tuber infections from late blight. It also has higher protein and vitamin C concentrations than Ranger Russet, Russet Burbank and Russet Norkotah, indicating that it can provide an enhanced level of dietary protein and vitamin C relative to these standard potato varieties. Pomerelle Russet has moderate specific gravity and good resistance to sugar ends. It also has moderately long dormancy, about 30 days shorter than Russet Burbank. Average post-harvest processing ratings for Pomerelle Russet were similar to Ranger Russet and greater than Russet Burbank. Pomerelle Russet also has maintained acceptable fry color for about 180–200 days in storage at 8.9 °C, indicating potential for processing out of mid-term storage, with improved fry color uniformity relative to industry standards. However, its primary use appears to be as a high quality, early fresh variety.     

Potato tuber sugar content during development and storage (10°C): possible predictors of storage potential and the role of sucrose in storage hexose accumulation

Summary Reducing sugar and sucrose contents of potato tubers (Solanum tuberosum L.) from six cultivars were monitored both during the growing season and after a four months storage period at 10°C. Significant correlations were found between tuber sugar contents (sucrose, reducing and total) measured at harvest and the reducing sugar content after storage. Similarly, in five of the six cultivars, the sucrose loss and the corresponding reducing sugar gain during storage were significantly correlated.     

Potato composition: II. Tissue selection and its effects on total sugar,total reducing sugar,glucose, fructose and sucrose contents

American Journal of Potato Research - Total sugar, reducing sugar, glucose, fructose, and sucrose were determined in three parts (bud-end, stem-end, and core) of tubers of White Rose, Red La Soda,...     

Potato virus X infection of Netted Gem potato

When Netted Gem potato plants were inoculated with potato virus X 7 to 31 days before defoliation the tubers were not uniformly infected. Testing of a single germinating eye chosen at random from each tuber detected fewer than half of the tubers from which stem-end, mid, or apical-end sections produced infected plants. The number of completely and partially infected tubers increased as the length of time between inoculation and defoliation was increased. Infection was not correlated with tuber size. Partially infected tubers produced equal numbers of infected plants from stem-end and apical-end sections.     

Influence of low fertility and vine killing on sugar development in apical and basal portions of Russet Burbank potatoes

Russet Burbank tubers from plants which died prematurely (low fertility plots) accumulated significantly greater amounts of reducing sugars in storage than tubers from plants which were adequately fertilized. Also, a significantly greater difference in relative amounts of reducing sugars between the apical and basal portions was obtained from tubers of the low fertilizer regime. The basal portion had a three times greater amount of sugars than the apical portion. This is of particular interest to processors of French fries who try to obtain uniformity of color in processed fries. The difference in total reducing sugar accumulation in storage between tubers of high and low fertilizer regimes was greater at the lower storage temperatures. Tubers allowed to mature in the ground (second harvest date) accumulated less sugars in storage than tubers dug shortly after vine kill.