A rapid method for determining blackspot susceptibility of potato clones

Two methods of determining susceptibility of potato clones to blackspot were compared: (1) bruising by weight dropping and (2) bruising by abrasive peeling. A highly significant positive correlation was obtained between the intensity of enzymatic discoloration following abrasive peeling and the amount of blackspot that developed by weight dropping (r=0.93). Abrasive peeling was more rapid than the weight-dropping method. Tuber samples were abraded 30 sec and the amount of enzymatic discoloration evaluated after 24 hr. The need for individually bruising and hand peeling of tubers was eliminated with this method. Because of the rapidity of the abrasive peeling method, it can be used effectively in potato breeding programs to screen large numbers of clones for blackspot susceptibility. Results indicate that tuber maturity affects enzymatic discoloration and blackspot susceptibility. Immature tubers, dug while the vines are still green, are more resistant to blackspot than mature tubers. Tuber maturity therefore must be considered when screening clones for susceptibility to blackspot.     

Fresh Market Evaluation of Six Russet-Type Potato Varieties and Four Russet Norkotah Strains

In 2016, Russet Norkotah was the second most widely grown potato variety in the US; however, recent research has identified alternatives with excellent production economics. During 2011–2013, fresh market variety research was conducted in the Columbia Basin of central Washington, a long-season production region. Russet Norkotah was compared to five varieties–Classic Russet, Mountain Gem Russet, Russet Burbank, Targhee Russet, and Teton Russet–and four sub-clonal strains–CO-3, CO-8, TX-278, and TX-296–derived from Russet Norkotah. Each variety was evaluated for early- (104 days between planting and vine kill) and late- (150 days between planting and vine kill) harvest tuber size profile, grade, and yield, grower economic value, susceptibility to blackspot bruise and shatter bruise, emergence, stem and at-harvest tuber numbers, tuber length-to-width ratios, and quality. When harvested early, Classic Russet and Mountain Gem Russet produced 30% and 15% more gross revenue than Russet Norkotah, respectively. All other varieties and Russet Norkotah strains except CO-3 produced as much early-harvest gross revenue as Russet Norkotah. CO-3 early-harvest revenue was close to 50% lower than that of Russet Norkotah. All varieties and Russet Norkotah strains produced significantly greater late-harvest yields and gross returns than Russet Norkotah. Late-harvest gross revenue for Targhee Russet and Mountain Gem Russet was 38% and 34% higher than Russet Norkotah, respectively. Classic Russet, Mountain Gem Russet, Targhee Russet, and Teton Russet had significantly more shatter bruise following the late harvest than Russet Norkotah and all Russet Norkotah strains. Russet Burbank was among the most susceptible to blackspot and Targhee Russet the least, with 32% and 2.1%, respectively. If bruising is mitigated, Mountain Gem Russet, Classic Russet, and Teton Russet may be suitable alternatives to Russet Norkotah and Russet Norkotah strains for both early and late harvests.     

Somerset: A new chipping potato variety

The Somerset potato variety is a medium-maturing variety with attractive, round to oblong, white-skinned, white-fleshed tubers with shallow eyes. Its major use is expected to be as a chipping variety in areas where potatoes are stored for some length of time, since its sugar content is lower than most varieties during storage, and it can be chipped after six months in storage. Somerset does not show the net necrosis caused by potato leafroll virus, and is immune to race 0 of Phytophthora infestans (late blight). Somerset is also moderately resistant to infection by Alternaria solani (early blight), and is only moderately susceptible to Verticillium wilt. Somerset is more susceptible to both common and acid scab than Superior, but less susceptible than Kennebec and Katahdin. It also has shown susceptibility to skinning and shatter bruise, but does not have a strong blackspot bruise reaction.     

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.     

Factors contributing to the blackspot bruise potential of Idaho potato fields

Blackspot bruise is a major problem in the fresh market and frozen french fry industry. The blackspot bruise potential of Russet Burbank and Ranger Russet in Idaho potato fields was determined by surveying commercial fields during 1993 and 1994. Management factors were monitored to determine what practices were contributing to blackspot susceptibility in addition to mechanical damage. The survey included 17 Russet Burbank and 3 Ranger Russet fields in 1993, and 28 Russet Burbank and 8 Ranger Russet fields in 1994. The 1993 season was unusually cool and wet whereas 1994 was warmer than normal, resulting in a wide range of environmental conditions for the 2 year study. Blackspot bruise potential was determined at different stages of tuber physiological maturity by collecting samples several weeks prior to normal harvest, immediately before harvest, and after storing sub-samples for several months. The blackspot bruise potential was measured by both impact and abrasive peel tests. Field maturity was the factor most consistently related to blackspot potential both years. In 1994 a multiple regression of 3 independent variables — field maturity index, specific gravity, and percent available soil water at tuber sampling, compared with the blackspot potential as the dependent variable gave a correlation coefficient of r = 0.73 (p = 0.001). Due to the cool, wet growing season in 1993, there was not enough variability in specific gravity and available soil water among the fields sampled for these factors to correlate with the blackspot potential. The available fertility data, although not complete for all fields, indicated no direct relationship between N, P, or K fertilization and blackspot potential. Preharvest samples in late August had lower blackspot potential than harvest samples in mid September, and storage samples in February had the highest susceptibility. There was a consistent increase in blackspot severity when tubers were equilibrated at 4 C compared with 10 C prior to bruising.     

Effets of soil potash treatment and storage temperature on blackspot bruise development in tubers of fourSolanum tuberosum cultivars

Plots of Russet Burbank, Nampa, Targhee, and A6371-2 received O, 250, and 500 lb of potash (K₂O/A as KC1 or K₂SO₄). Tubers were bruised following harvest. Potash treatment had no significant effect in reducing blackspot development when there was no yield response to K fertilization. On soil that tested low for K, potash treatment significantly reduced blackspot development for all four cultivars. Tuber subsamples were bruised after 6 mo in storage at either 1.7 or 10 C. Differences in blackspot bruise development between low and high K were maintained for those tubers stored at 10 C; differences were not maintained and little discoloration developed in tubers stored at 1.7 C, due perhaps to less enzyme activity and less substrate. The Nampa cultivar was significantly more resistant to blackspot than the other three cultivars.     

The effect of potassium deficiency on chemical, biochemical and physical factors commonly associated with blackspot development in potato tubers

Blackspot bruise is a physiological disorder of potato tubers resulting from mechanical damage to tissues during handling. This study examined the effect of potassium nutrition on biochemical and physical changes normally associated with blackspot bruise in potato tubers. Four potato (Solanum tuberosum L.) genotypes (TXA 763-5 [very resistant], Ranger Russet [very susceptible], Russet Burbank [susceptible], and Lemhi Russet [very susceptible]) differing in susceptibility to blackspot bruise were grown at three potassium nutrition levels (100%, 10% and 0% of the potassium in full strength Hoagland’s solution). Tubers from the three treatments were tested for their chemical, biochemical and physical characteristics commonly related to blackspot bruise susceptibility. The potential to develop malanin pigments was measured as total oxidative potential (optical density, OD₄₇₅) of clarified tuber homogenates. Tuber tissue extracts were assayed for polyphenol oxidase (PPO) activity with catechol, measured as increase in OD₄₁₀ over time. Specific gravity of tubers was determined with a brine solution series. Physical property measurements were made by impacting cores of tuber tissue in a specially designed instrumented pendulum. Shock wave speed, Young’s modulus, failure stress, and failure strain were all measured dynamically during impact. Tubers produced under both the 10% and 0% potassium regimens had almost 2x the free tyrosine of control tubers. The 0% potassium tubers had significantly higher PPO activity than the control. Both of these factors likely contributed to the significantly higher total oxidative potential that was observed in tubers from both the 10% and 0% potassium treatments. Tubers from both the 0% and 10% potassium treatments had a significantly lower Young’s modulus (a measure of stiffness), significantly lower failure stress and the shock wave of impact propagated through both of them significantly slower. Although the cultivars were significantly different in their susceptibility to black pigment development, they all responded similarly to the treatment with regards to the variables measured. The TXA-763-5 clone was much more susceptible to developing black pigments in these tests than expected. The other three cultivars performed as they do in commerce.     

Red Pearl: A new gourmet red potato variety

Red Pearl is a medium-late variety with round tubers of stable dark red skin and white flesh. It is an ideal gourmet and canning variety due to its high tuber set and high proportion of tubers less than 4.76 cm diameter (up to 71% of the total yield). Red Pearl has good boiling and baking qualities. Its specific gravity is slightly higher and the tuber dormancy is longer than Dark Red Norland. Red Pearl yields only 54% to 77% of Red Norland because of its small tuber size. Red Pearl is less susceptible to common scab (Streptomyces scabiae < than Dark Red Norland, significantly more resistant to corky ring spot (tobacco rattle virus) than Dark Red Norland and is resistant to bacterial wilt and brown rot (Ralstonia solanacearum). Red Pearl showed similar susceptibilities to several other diseases, including early blight, late blight, pink rot, and tuber soft rot, compared to Dark Red Norland. Red Pearl is more susceptible to shatter bruise and blackspot than Dark Red Norland when handled from storage at 7.2 C.     

RBM134: A mutant of Russet Burbank susceptible to blackspot bruise

A radiation induced mutant of Russet Burbank was recovered that is more susceptible to blackspot bruise than the original cultivar. The mutant was evaluated and characterized for several agronomic and biochemical traits. Compared to Russet Burbank the mutant had slightly lower tuber yield, smaller average tuber weight, a higher number of tubers per plant, higher percent tuber dry matter, similar total tuber dry matter yield, lower tuber protein and higher free tyrosine content. Vine growth and appearance was indistinguishable from Russet Burbank. This mutant should provide an excellent tool for better understanding the tuber characteristics contributing to blackspot bruising in potatoes.     

Millennium Russet: A dual purpose russet potato variety

Millennium Russet is a medium-late variety with long tubers having light russet skin and white flesh. It has potential as a fresh market and processing (french fries) variety. The tuber type of Millennium Russet is similar to Russet Burbank, but with better external and internal quality. The marketable yield, tuber set, and specific gravity are higher than Russet Burbank. Tubers show good fry color when processed from cold storage (7.2 C). Millennium Russet has a bland flavor and is less mealy and discolored than Russet Burbank. Chemical maturity of Millennium Russet occurs at approximately the same time as Russet Burbank, but it has lower sucrose levels in the bud and stem end. The glucose levels of Millennium Russet were 50% less than Russet Burbank throughout the first 4 months of storage at 10 C. Low glucose levels in the stem end of Millennium Russet when processed out of storage suggest tolerance to stress and low vulnerability to sugar end. Millennium Russet is resistant to common scab and corky ring spot, moderately resistant to dry rot, pink rot, and black scurf, and moderately susceptible to Verticillium wilt, bacterial wilt and brown rot. Millennium Russet is more sensitive to blackspot bruise than Russet Burbank, but more resistant to shatter bruise. Tuber yield of Millennium Russet was less responsive to nitrogen rates when compared with Russet Burbank, but tuber size distribution was more responsive to increases in in-row spacing.     

Differences in free and protein-bound tyrosine among potato genotypes and the relationship to internal blackspot resistance

Twelve potato clones were selected to represent the full range of internal blackspot response in order to determine the relationships between tuber protein, free tyrosine, and blackspot susceptibility. The blackspot reaction for each clone was consistent over five growing seasons, including tubers grown over a normal season (mature), and short season (immature) during one year. The blackspot index, determined by either an abrasive peel test or an impact bruise test, was highly correlated with the tyrosine content of the tubers (r = 0.90 p = 0.001 for the means of each clone over five location-years). Tubers with free tyrosine levels below 4 μmole/g dry weight consistently showed a resistant blackspot response. The relationship between tyrosine and blackspot susceptibility was also found in stolon and bud ends from five of the clones which represented the extremes of blackspot reaction and genetic diversity. Bud end samples of each of the clones had lower tyrosine content and a corresponding reduction in blackspot compared with stolon ends. Phenols, other than tyrosine, showed no consistent relationship to the blackspot reaction. There was a very high negative correlation between free tyrosine and estimated protein-bound tyrosine. R values ranged from ?0.85 to ?0.97 (p = 0.001) for mature tubers of the 12 clones over 4 growing seasons. Total tyrosine (free, plus protein-bound) remained relatively constant. There were no significant differences in mean total tyrosine content among the 12 clones over five location-years of testing; and there were no significant differences among the five growing seasons except for the short season (immature) tubers which were 14% lower in total tyrosine content. These results indicate a remarkably constant level of total tyrosine production in the twelve clones studied, that represented diverse genetic backgrounds. Mature tubers of all genotypes contained 26 ± 1 μmole/g dry weight total tyrosine. Partitioning of tyrosine between tuber protein and the free amino acid pool varied with genotype and appeared to be a major determinate of blackspot resistance.     

Summit Russet: A new russet potato variety with good fresh market and frozen processing qualities

Summit Russet (A84118-3), the result of the cross A77236-6 x TND329-1Russ, was released in 2003 by the USDA/ARS and the Agricultural Experiment Stations of Idaho, Oregon, and Washington. The vines of Summit Russet are erect, with very thick stems, large yellowish-green leaves and abundant white flowers. The tubers are tan, with medium russet skin, long-flattened shape, a slightly prominent eyebrow, white flesh, and moderately prominent pith. Tuber dormancy is very long. Summit Russet was compared with Russet Burbank in trials across the Pacific Northwest for yield, quality, and disease response. In general, Summit Russet produced similar or lower total yields than did Russet Burbank, but higher U.S. No. 1 yields. In Idaho variety trials, Summit Russet exhibited resistance to second growth, growth cracks, blackspot bruise, and stem-end discoloration, and moderate susceptibility to hollow heart and shatter bruise. In comprehensive product quality evaluations, Summit Russet was rated superior to Russet Burbank for french fry quality and similar for baked potato quality. French fry quality was retained after long-term storage. In replicated disease trials, Summit Russet was found to have good resistance to common scab, early blight tuber rot, and Verticillium wilt, and moderate resistance to Fusarium dry rot and tuber net necrosis caused by PLRV. It demonstrated susceptibility to late blight, foliar PLRV, PVX, PVY^o, and bacterial soft rot. Biochemical analysis of Summit Russet tubers showed them to be higher in total solids and sucrose, and lower in dextrose than those of Russet Burbank. Tuber glycoalkaloid concentration as measured from tubers produced in 1994–1996 trials was 6.7 mg 100 g¹.     

Potato vine kill: Stem-end discoloration effects on Russet Burbank

The relationship of potato (cv. Russet Burbank) tuber stem-end discoloration to speed of vine kill and maturity of vines when killed was studied for three years at several sites in Idaho. Discoloration due to leafroll was separately determined. Vine killing with sulfuric acid, dinoseb, endothall and hand pulling produced a range in killing speeds from fast to slow. Vine kill speed alone did not affect amounts of discoloration. Vines that died naturally from frost or other causes had as much discoloration (14% over all treatments) as from any chemical or mechanical vine killing method. The tendency for tuber discoloration increased when vines were less mature when killed.     

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     

Western russet: A new potato variety with excellent fresh market and frozen-fried processing quality and field resistance to common scab and PVYo

Western Russet, designated experimentally as A7961-1, and resulting from the cross A68113-4 x Bel-Rus, was released in 2004 by the USDA/ARS and the agricultural experiment stations of Idaho, Oregon, and Washington. The foliage of Western Russet is spreading, with medium-sized olive-green leaves and abundant white flowers. The tubers are tan, with medium russet skin, oblong shape, a slightly prominent eyebrow, white flesh, and distinctly visible pith. Western Russet was compared with Russet Burbank in trials across the Pacific Northwest for yield, quality, and disease response. In general, Western Russet produced lower total yields than Russet Burbank, but on average and depending on location, similar U.S. No. 1 yields. When observed for defect problems, Western Russet exhibited resistance to second growth, growth cracks, shatter bruise, stem-end discoloration, and heat necrosis, moderate resistance to hollow heart, and moderate susceptibility to blackspot bruise. In product quality tests, Western Russet was rated similar to Russet Burbank for french fry and dehydrated potato flake quality and slightly inferior for baked potato quality. In replicated evaluations, Western Russet was found to have good field resistance to common scab and PVY^o, and moderate resistance to verticillium wilt and tuber net necrosis caused by PLRV. It demonstrated susceptibility to late blight, foliar PLRV, dry rot, soft rot, and tuber early blight. Biochemical analysis of Western Russet tubers showed markedly higher vitamin C content than those of Russet Burbank. Tuber glycoalkaloid concentration in tubers produced in a 1988 trial was 1.0 mg 100 g^?1.     

Anatomy and compositional variations within potatoes. IV. Total solids distribution in different cultivars

Distribution of cortical, perimedullary, and pith tissues and total solids content were determined on both a fresh and a dry weight basis for six potato cultivars grown concurrently in three locations in California. At one location, tubers harvested 80 days from planting were 1.0 to 2.5% lower in total solids than tubers harvested at later dates. The high solids cortical tissues ranged from 39 to 51% of whole tubers on a dry basis, and the amount appeared to be related to tuber shape. White Rose and Red LaSoda showed greater difference in per cent total solids between cortical and perimedullary tissues than did Kennebec, Lenape,³ Norchip, and Russet Burbank. The high total solids of the cortical tissues is particularly significant to processing losses. Any method of peeling that removes one half the linear depth of the cortical tissues can result in a loss of 25% or more of total tuber solids, depending upon cultivar and tuber shape. Tuber development and distribution of total solids and other components were previously described for Red Pontiac, Russet Burbank, and White Rose tubers obtained from the retail market (6,9,10,11). It was particularly noted that the high-solids cortical tissues, although averaging only about 6mm in depth, comprised between 40 and 50% of both fresh and dry tuber weights (6,11). Because this sort of distribution of solids is especially significant to peeling loss, possible differences in solids among cultivars and at different harvest dates were investigated.     

Use of enzyme-linked immunosorbent assay to detect potato leafroll virus in field grown potato,cv. Russet Burbank

Use of enzyme-linked immunosorbent assay (ELISA) in detecting potato leafroll infections in field grown potato, cv. Russet Burbank, was studied from 1986 to 1988 at Rosemount, Minnesota. The objective was to determine relative reliability of current season foliage ELISA, tuber tissue ELISA, and tuber progeny foliage ELISA. Serological tests were most accurate when foliage of tuber progenies was tested. ELISA underestimated total leafroll infection when current season foliage from the inoculated plant was used, in those plants inoculated during late tuber bulking stage. Current season foliage ELISA tests using newly expanded terminal leaflets were more reliable than were tests using older leaflets. Leafroll infection was detected in the current season foliage and tuber progenies (tuber tissue as well as tuber progeny foliage) of some plants seven days after inoculation. Most current season foliage infections were detected by day 14–28 depending on year. Differences among years were most likely caused by variation in quality of virus source plants and numbers of vectors used in inoculation. ELISA tests on tuber tissue were almost as effective as ELISA tests on tuber progeny foliage in detecting potato leafroll 20 days after inoculation, but ELISA on tuber tissue substantially underestimated infection if plants were sampled earlier. Maximum percent tuber infection occurred 20 days or more after inoculation. Movement of the virus from the inoculated stem to other stems decreased with increased plant age at inoculation. Percent infected tubers declined with increased plant age at inoculation. Action thresholds developed for aphids in managing potato leafroll virus should take into account the temporal change in percent infected tubers.     

Laboratory testing of potato tubers for multigenic resistance to late blight

Resistance in the tubers of potato clones with various levels of foliar multigenic resistance toPhytophthora infestans was measured to detect possible correlations between tuber and foliar resistance. A highly significant correlation was found using wound-healed tuber tissues. High levels of tuber resistance were detected in most foliar-resistant clones when inoculations with race 1,2,3,4 were made after 24–48 hours of wound periderm formation at 20 C. The resistance of wound-healed tissues increased as the time between wounding and inoculation increased. This increase in resistance was significantly greater for clones with foliar resistance than for clones with susceptible foliage.     

Irrigation,nitrogen and gypsum effects on specific gravity and internal defects of Atlantic potatoes

Irrigation, nitrogen and gypsum were investigated in a 3-year study to determine their influence on specific gravity and internal physiological defects. Excess irrigation during August and September reduced specific gravity, increased the incidence of hollow heart, and in some years, internal brown spot. Tuber yields were not significantly affected by excess irrigation. Exclusion of late season irrigation, however, significantly reduced tuber yields. No consistent yield response to nitrogen was evident, but a response up to 168 kg/ha was observed in 1987. Nitrogen rate did not effect hollow heart, internal brown spot or chip color. The incidence of internal brown spot in the tubers of check treatments was quite variable from year to year, and ranged from 8 to 21%. The lowest incidence of internal brown spot observed in 1989 coincided with the highest calcium levels in the tuber peel. Although gypsum treated potatoes had reduced incidence of internal brown spot, the effects were partial and inconsistent. Significant increases in peel and petiole calcium concentrations in the gypsum treated plots only occurred in one year. The peel calcium levels appeared to be influenced more by the season and to a lesser extent by gypsum. Gypsum applications produced no effects on total or US#1 tuber yield, specific gravity, hollow heart, or chip color. Preliminary data also suggested that gypsum did not markedly influence the incidence of blackspot. Based on this study, a routine gypsum application to improve the tuber quality of the variety Atlantic is not recommended.     

Objective measurement of texture variables in raw and processed French fried potatoes

The five most important variables encountered in french fry production and texture measurement are: specific gravity, raw potato storage, raw potato firmness, freezing of fried product, and cooling of hot french fry slices. Shear force curves are presented to illustrate the effects of these variables. A double maximum cruts shear peak is exhibited by properly processed french fried potatoes when they are hot. Bursting of the crust is less evident with less desirable fries and with frozen and reheated samples. Shear press punch tests proved to be best for analyzing raw potato firmness. In order to determine and study the texture variations within a potato, Durometer³ tests were conducted on concentric zones and sections from bud to stem end of most firm and least firm raw tubers. Higher resistance to penetration was encountered in the most firm potatoes. Durometer values vary directly with solids within a tuber which can be explained by certain morphological conditions. Because of turgidity, however, solids and Durometer values vary inversely between firm and non-firm tubers. A table is presented which lists the texture inferences derivable from changes which occur in the french fried potato shear force curves.