Rates of internal blackspot bruise development in potato tubers under conditions of elevated temperatures and gas pressures

Internal blackspot bruising was produced in Russet Burbank tubers by dropping a 150 g weight 40 cm through a slotted guide tube and incubating the tubers for varying time periods at temperatures ranging from 10 to 80 C. When potatoes were bruised following 1 to 5 months storage, those tubers incubated at 10 C required 48 hr for maximum blackspot development. Increasing the incubation temperature accelerated blackspot formation with an optimum response at 36 to 40 C. At 40 C tubers reached maximum discoloration within 6 hr. Bruised tubers were also exposed to combinations of varied temperatures and varied gas pressures of 0.3 to 2.1 kg/cm² using air, O₂, CO₂, and N₂. Pressurized air slightly enhanced the temperature effect at 40 C; pressurized O₂ had no significant effect upon blackspot development, while CO₂ and N₂ inhibited blackspot formation. Blackspot bruises incurred in the field during harvest required a longer incubation period at a lower temperature than did bruises inflicted on tubers held in storage for 1 to 5 months.     

The effect of edaphic and genetic factors on the phosphorus components in potato tubers

Clonal lines of five potato cultivars were grown in four locations differing in soil types. The effects of locations and cultivars on the phosphorus fractions of the tubers were determined. Large differences were found in total and inorganic phosphorus. Within the organic phosphorus fraction, greatest variability was found in phytic acid and in starch associated phosphorus. With respect to components of variation, the locality appeared to be the dominant factor in determining levels of total, inorganic and phytic acid phosphorus. The cultivar contribution to these fractions was also significant. Starch-associated phosphorus appeared to be affected by locality and cultivar to about the same degree. However, nucleic acid phosphorus and lipid phosphorus were not affected by either locality or cultivar.     

Distribution of oxidase enzymes in potato tubers relative to blackspot susceptibility II. Peroxidase and Catalase

Peroxidase and catalase activities in selected potato tuber tissue were studied for differences and possible association with resistance or susceptibility to blackspot. Unbruised stem-end tissue had significantly greater peroxidase activity than did unbruised bud-end tissue. However, there was no significant difference between catalase activity at either end of the tuber; between blackspot susceptibility and peroxidase or catalase activity; and between blackspot susceptible or resistant tissue and the ratio of either catalase or peroxidase to phenolase activity. Bruising did not cause significant changes in either peroxidase or catalase activity or in ratios between these enzymes and phenolase that could be associated with susceptibility or resistance of tissue to blackspot. Studies associating enzymes with potato blackspot susceptibility have been concerned primarily with phenolases (5, 6, 10, 11, 13). Only recently has blackspot susceptibility been considered in connection with activity of other oxidase enzymes (12). It has been known for many years that peroxidase could oxidize many of the same phenols as the phenolases and produce a colored pigment very similar to melanin (7, 8). The study by Weaver et al. (12) was concerned with the possibility of peroxidase contributing to or subtracting from enzymatic discoloration of bruised potato tissue. The study also investigated the inhibitory or accelerating effect of H₂O₂ per se on the rate of oxidation of different phenolic substrates by potato enzymes, and how such reactions could be modified by addition of catalase or peroxidase. The theories of how peroxidase and catalase could contribute to susceptibility to blackspot were also discussed. The purpose of this study was to determine if potato peroxidase or catalase activityper se differed in various parts of the tuber, if these activities could be associated with resistance or susceptibility of the tissue to blackspot, and if certain relationships could be established to predict the response of potato tissue to bruising.     

Improvement of techniques for potato blackspot evaluation and some errors associated with measurements

Potato blackspot is a sub-epidermal blackening of tissue that results when bruising forces rupture cells of susceptible tubers. Degree of blackspot susceptibility is measured by bruising tubers and assessing the amount of discoloration that develops. Since the rate of color development is influenced by temperature, all testing was done at 21 C. Blackspot intensity was evaluated by visual inspection and by use of a photo reflectometer. A high correlation exists between reflectometer measurements and visual observations. The thickness of the paring slices affected the accuracy of susceptibility inferences. For spots ranging from 10 to 15 mm in diameter a shaving error of ± 1 mm would cause an error of about 5%, whereas on spots 5 mm or less such a shaving error would cause an error of about 20%. Reduction in peel thickness can reduce such errors appreciably. The variability in susceptibility to blackspot varies greatly both within a tuber and among tubers. In these studies 30 bruises in selected tuber locations were adequate to measure treatment differences. About 30 spots, whether obtained by bruising each of 10 tubers 3 times or by bruising 30 tubers once, resulted in about equal blackspot scores. Improvements in a previously described method for bruising and evaluating potato tuber blackspot susceptibility are described.     

The effect of CCC on the initiation of potato tubers

Summary CCC, when applied to the roots of potato plants sufficiently early, brought forward the time of tuber initiation and growth. An increase in net assimilation rate at the time of rapid tuber growth was found for both CCC treated and control plants.     

The effect of glyphosate on the viability of seed potato tubers

Summary Glyphosate applied to a growing crop of potatoes adversely affected the growth of the harvested tubers in the following season. Some effects were produced at 0.018 kg/ha^*, equivalent to ca 1 % of a commercial application rate. Symptoms were more severe at higher rates.     

The effect of chloride fertilization on blackspot susceptibility and other quality characteristics and on yield of potato

Summary Trials were carried out in two years on a sandy loam and on a heavy clay soil with two cultivars to examine the potential of chloride fertilization as a tool to reduce blackspot susceptibility of potatoes and to investigate other effects on yield and quality. Blackspot susceptibility was significantly reduced in cv. Marijke, but not in cv. Bintje as a result of increasing doses of applied chloride from 0 to 400 kg ha1. Dry matter concentration, assessed as under-water weight, was reduced by chloride in both cultivars at the two locations. Fry colour of French fries was improved by chloride. Applying 400 kg ha⁻¹ Cl⁻ to both soil types decreased net tuber yield >35 mm of cv. Bintje but not of cv. Marijke. Chloride caused slower emergence, retarded crop development and less stems per plant on the sandy loam soil but not on the heavy clay soil.     

The influence of storage factors on endogenous ethylene production by potato tubers

Throughout a 7-month storage period, Russet Burbank tubers continuously ventilated at 32 F (0 C) and 45 F (7.2 C) with atmospheres of 2% O₂, air, 4% CO₂, and intermittently ventilated with air, evolved ethylene at a rate no greater than 0.008 μ 1 Kg^?1 hr^?1. Tubers stored in 80% O₂ and 12% CO₂ produced ethylene at much higher rates. In all cases where sprouting occurred, the rate of ethylene production increased. Inoculation withFusarium roseum greatly stimulated ethylene production but inoculation withAlternaria solani did not.     

Net necrosis of potato tubers associated with primary,secondary, and tertiary infection of leafroll

Tuber net necrosis, caused by leafroll virus, was found to occur as a result of primary, secondary, and tertiary infection in six clones of potato (Solanum tuberosum L.). Differences were observed between clones in their reaction to the different types of infection. In most clones there was a higher percentage of net necrosis from primary than from secondary or tertiary infection. No significant difference was observed in the severity of the net necrotic symptoms due to the different types of infection.     

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.     

Effects of nitrogen,phosphorus and potassium fertilizer treatments on weight loss and changes in chemical composition of potato tubers stored at 4°C

Summary Pot and field experiments were carried out to test fertilizer treatments on the behaviour of potato tubers stores at 4°C and ≥90% relative humidity for 6 months. Weight losses (separated into water and dry matter) were enhanced after N and K fertilization and decreased by increasing P supply. Glucose and fructose contents were reduced at harvest by high N-fertilizer rates compared to no or low fertilization, but throughout storage reducing sugar accumulation was increased, sucrose reduction was decreased and ascorbic acid was increased. K fertilization affected the chemical composition of the tubers somewhat similar to that of nitrogen fertilization. High initial nitrate content of the tubers seemed to be increased and low nitrate values were decreased during storage. The tubers from pot experiments showed similar changes but of greater magnitude.     

The effect of potato virus X on susceptibility of potato tubers toFusarium roseum ‘Avenaceum’

Potato virus X (PVX)-free and mild PVX-infected tuber lines originating from the same Katahdin clone were compared for susceptibility to tuber rot incited byFusarium roseum (Lk.) Synd. and Hans. ‘Avenaceum’. The effect of interval between top-kill and harvest on development ofFusarium tuber rot was also determined. A series of tubers from both PVX-free and PVX-infected tuber lines was either (i) mechanically bruised and inoculated by immersion in a spore suspension ofF. roseum ‘Avenaceum’, (ii) mechanically bruised but not inoculated, (iii) inoculated only or (iv) neither bruised nor inoculated. Tubers from all treatments were then stored at temperatures of 18–21 C (65–70 F) for a 3-week period prior to being placed at 4 C (39 F) for the remainder of the storage period. The amount of rot was determined after a 5–6 month storage period at the latter temperature. In a 4-year study PVX-free tubers were significantly (1% level) more susceptible to infection byF. roseum ‘Avenaceum’ than tubers infected with mild PVX. PVX-free tubers left in the ground for 2 or 3 weeks after top-kill were significantly (1% level) more susceptible toFusarium dry rot than those infected with the virus; however, there was no significant difference in disease incidence between PVX-free and PVX-infected tubers when harvested 4–5 weeks after top-kill. Tubers, both PVX-free and PVX-infected, remaining in the ground for a 2 week period following top-kill were significantly (1% level) more susceptible toFusarium tuber rot than those harvested 3 weeks after top-kill; similarly, both PVX-free and PVX-infected tubers harvested 3 weeks after top-kill were significantly (1% level) more susceptible than those left in the ground for a 4–5 week interval.