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.     

Influence of temperature and length of storage on resistance of potato to tuber rot induced byErwinia chrysanthemi

Tubers of 11 clones ofSolanum tuberosum subsp.andigena (andigena) and 12 cultivars ofS. tuberosum subsp.tuberosum (tuberosum) were inoculated with water suspensions (5.5 × 10⁴ 5.5 × 10⁵, 5.5 × 10⁶ CFU/ml) ofErwinia chrysanthemi. Tubers were inoculated immediately after harvest and after 6 and 16 wk of storage at 4 and 23°C. Tuber rot incidence in andigena and tuberosum increased as inoculum concentration increased. Based on tuber rot severity, clones of andigena were classified as resistant, intermediate, or susceptible and cultivars of tuberosum were classified as intermediate or susceptible. Rot severity increased in all tubers stored at 4°C and in tubers of tuberosum stored at 23°C; rot did not increase in tubers of andigena stored at 23°C. Electrolyte leakage (EL), total sugars (TS), reducing sugars (RS), non-reducing sugars (NRS) and dry matter (DM) were determined in non-inoculated tubers. There was a significant positive correlation between the rate of EL, concentration of RS and tuber rot in andigena and tuberosum. Tuber rot and DM were negatively correlated in tubers of andigena; but they were not correlated in tuberosum. Clones of andigena with low EL, TS, RS, and high DM were resistant to tuber rot, and the incidence of tuber rot in these clones was much less influenced by temperature and length of storage. The influence of temperature and length of storage on susceptibility toE. chrysanthemi may be explained by increased cell membrane permeability; increased leakage of accumulated sugars in potatoes stored at 4°C could favor bacterial proliferation resulting in more disease.     

Influence of fertilizer,irrigation, and storage treatments on nitrate-N content of potato tubers

A survey was undertaken to investigate the nitrate-nitrogen (NO₃-N) content of potatoes grown on different soil types with different fertilizer and irrigation treatments. Tuber nitrate-N contents were determined immediately after harvest and after periods of storage of up to 210 days. Nitrate-N in tubers (dry weight basis) ranged from low values of 82 to 122 ppm for low nitrogen fertility levels to a maximum of 192 to 285 ppm at the highest nitrogen rates, where irrigation was applied at optimum levels. The average nitrate-N in tubers under such conditions was 150 to 160 ppm. Where irrigation management was less than optimum, the nitrate-N content of tubers increased, reaching an average maximum value of 786 ppm at the highest fertilizer rate. The study showed that the nitrate-N level in tubers increased with nitrogen fertilization rates, although there was not a linear relationship between N fertilizer rate and tuber nitrate-N. The highest nitrate-N levels obtained in the tubers under proper irrigation management, even with 800 lb N/A, did not exceed 300 ppm nitrate-N and were usually less than 200 ppm. Data collected from this study suggest that improper irrigation, especially with high nitrogen fertilizer rates, results in a dramatic increase in nitrate-N level in the tubers. Some individual tubers contained over 1200 ppm nitrate-N. There was an apparent slight increase in nitrate-N in the tubers with storage, although this increase was not consistent.     

Metalaxyl and other fungicides for control ofPhytophthora infestans on potato in northwest Washington State

In northwest Washington State, fungicidal control of late blight caused byPhytophthora infestons was evaluated for three years. During 1977, a high rainfall year with supplemental sprinkler irrigations, all metalaxyl and chlorothalonil treatments reduced tuber rot at harvest, but only metalaxyl extended control of tuber rot after 4 months’ storage. During 1978, a high rainfall year, one application of metalaxyl sprayed over or dusted on potato seed pieces at planting or applied five times to foliage at 2 or 4 wk intervals gave excellent blight control equal to that with chlorothalonil applied to foliage every 2 wk. In 1979, a low rainfall year,P. infestons did not kill plants in untreated plots until October. Five applications of metalaxyl sprayed every 2 wk on foliage did not control foliage blight. However, metalaxyl reduced foliage blight when dusted on cut potato seed pieces. Mancozeb sprayed every 2 wk also gave excellent control. The possibility that metalaxyl applied to foliage is effective in late blight control only when washed into the soil by rainfall or irrigation for uptake by roots is discussed. Yields and percent U.S. No. 1 grade tubers were not significantly affected by any treatment in these 3-year trials.     

Phytophthora erythroseptica in Peru: Its identification and pathogenesis

EightPhytophthora isolates cultured from diseased potato plants and tubers in Peru were identified asPhytophthora erythroseptica Pethyb. var.erythroseptica. This pathogen was not previously reported from South America. The isolates were pathogenic to potato plants but they differed in virulence. Injuring roots prior to inoculation enhanced infection and disease development but all isolates infected noninjured roots. Continuous high soil moisture during incubation favored disease development. Under these conditions, disease developed at soil temperatures from 10 C to 30 C, but most rapidly at 25 C and 30 C. Plants grown 60 days before inoculation developed symptoms earlier and more rapidly than plants grown 15-, 30-, and 45 days. Four concentrations of mycelial-suspension inocula did not alter disease development, but zoospore inoculum induced symptoms and plant death more rapidly than mycelial suspensions at 25 C.     

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.     

Reaction of potato tuber slices toPhytophthora infestans in relation to physiological age

Tuber resistance toPhytophthora infestans was studied in relation to physiological age in tubers of the cultivars Atzimba, Katahdin, Kennebec, and Sebago. Resistance to race1,2,3,4 was evaluated in freshly harvested tubers, and tubers stored at 5 C for up to 215 days. Atzimba tubers were highly resistant when freshly harvested but became increasingly susceptible as they aged physiologically. Tubers of the other three cultivars were susceptible when freshly harvested and also when aged. Further, 57 tuber selections from among 11 crosses initially gave resistant reactions. However, after storage for six months at 5 C, 26.3% of the selections remained resistant, 22.8% were moderately resistant, 31.6% moderately susceptible, and 19.3% fully susceptible.     

Association of viral,bacterial and fungal pathogens with vascular discoloration of Russet Burbank potato tubers

Russet Burbank potatoes from the 1979 and 1980 crop years, collected from Chicago, IL repack warehouses and retail markets, were sampled for vascular discoloration. The amount of discoloration varied among sampling months and states of origin and decreased from 7.7% in 1979 to 1.6% in 1980. Highest levels of vascular discoloration were detected in December and January samples. Vascular discolored and non-discolored (control) tubers were assayed for the presence of potato leafroll, potato virus X, and beet western yellows viruses by the enzyme-linked immunosorbent assay (ELISA). Tubers were also assayed for 2 subspecies ofErwinia carotovora and forVerticillium albo-atrum andV. dahliae. Potato leafroll virus was detected in 31 of 831 vascular discolored tubers.V. albo-atrum was detected in 1 of 180 discolored tubers. Beet western yellows virus was not detected in discolored or non-discolored tubers. Two subspecies ofE. carotovora and potato virus X were equally common in discolored and non-discolored tubers.     

Pre-harvest chemical applications for control of tuber infection byAlternaria solani

Pre-harvest chemical applications significantly reduced populations of viableAlternaria solani spores on the soil surface in the laboratory and field and the infection of potato tubers in the field. Only formaldehyde consistently reduced spore germination and tuber infection in the laboratory and the field but Difolatan 4F, Difolatan 4F + DMSO (dimethyl-sulfoxide), Manzate D, Manzate D + DMSO and sodium hypochlorite often reduced fungus populations significantly. More work is necessary before pre-harvest chemical applications can be recommended for control of early blight tuber decay due to the variable performance of many chemicals and the relatively high cost and corrosiveness of formaldehyde, the most effective chemical in the study.     

Potato leaf and tuber water potential measurements with a pressure chamber

The use of a pressure chamber for measurements of water potential of potato (Solatium tuberosum L.) in leaves and tubers is described. For satisfactory results, evaporation from samples must be prevented prior to and during measurements, and samples must be measured quickly following detachment. Tubers were suspended in the chamber by their rhizomes for water potential measurements. Tuber water potentials appeared too low (dry) when rates of pressurization exceeded 0.05 bar sec¹ as the balancing pressure was approached (within 2 bars). Variations in measurements associated with the rhizome length, and with lack of equilibrium within the tuber, are discussed. Field measurements showed that under moderate to high transpiration, there was no simple relationship between leaf and tuber water potentials. In wet soil, tubers were wetter than leaves throughout the day. In dry soil, tuber potentials became as dry as those of leaves by the afternoon. Factors contributing to this changing pattern are discussed.     

Chemical control of pink rot of potato (Phytophthora erythroseptica PethyB.)

Field trials have been carried out for seven years to control pink rot (Phytophthora erythroseptica) at the International Potato Center (CIP). This disease has been a serious problem in the maintenance of a germplasm collection at the CIP’s Experimental Station at Huancayo, Peru (3300 m.a. s.l.). Pink rot annually causes serious loss of germplasm accessions, particularly diploid cultivars. Protective and systemic soil fungicides and soil fumigation with Basamid (Dazomet 98%) did not diminish the incidence of pink rot. Ridomil 5G (Metalaxyl 5%) applied at planting time with a preplanting fumigant reduced disease incidence from 31% of infected tubers to around 1%. Optimum control and yield increase were achieved by using Basamid at 300 kg/ha + Ridomil 5G at 30 kg/ha.     

Effect of daily irrigation rate and soil texture on yield and quality of Russet Burbank potatoes

Adequate soil water is needed for satisfactory yield and quality of potato tubers. With sprinkler irrigation systems it is common practice to apply more water than the crop uses in order to maintain high soil water levels. A study was initiated to evaluate the response of Russet Burbank potatoes to a wide range of daily sprinkler irrigation rates when grown on two soilsa loam and a sand—differing in water holding capacity. The results from the two soils were very different. On the loam soil, yields generally increased with increased applications of water, up to the equivalent of 40 to 50% estimated Et. Irrigation treatment effect on percent No. 1 tubers was inconclusive. In 1978, percent No. 1 tubers increased with water applied up to about 70% estimated Et. In 1980, irrigation rates between the equivalent of about 20 and 80% estimated Et had little effect on tuber grade. Yields and percent No. 1 tubers were depressed at irrigation rates greater than about 80% estimated Et. On the sand, yields and percent No. 1 tubers increased with increased irrigation rates up to about 100% and 80% estimated Et, respectively. Tuber specific gravity was not affected to an important degree by irrigation treatment on either soil. These results indicate that a good crop of potatoes can be grown on a loam soil at daily irrigation rates considerably less than estimated Et rates, while such reductions will decrease yields and grade on a sandy soil.     

Changes in endogenous abscisic acid,soluble sugars and proline levels during tuber dormancy inSolanum tuberosum L.

Abscisic acid (ABA), sucrose, reducing sugars and proline contents were monitored over an eleven-month period in tubers of three potato cultivars that varied in tuber dormancy. ABA and proline levels increased after top pulling the haulms and were not affected by harvest date. Proline did not change in either a storage temperature or cultivar-specific manner. The highest concentrations of ABA were found in tubers stored at 2°C while the lowest concentrations occurred in tubers stored at 20°C. At 10°C, the end of tuber dormancy in the cultivars Kennebec and Nooksack (but not Sebago) coincided with the decline in ABA content. There was no evidence of a threshold concentration of ABA below which sprouting would occur. Tuber samples of 10 different cultivars were removed from 10°C and placed in 20°C storage (in darkness). Initial ABA concentrations (i.e., at the time of removal from 10°C storage) were positively correlated with duration of dormancy and negatively correlated with subsequent rates of sprout elongation at 20°C. Sucrose content was negatively correlated with duration of dormancy. Reducing sugars responded primarily to storage temperature and did not appear to be related to dormancy or sprouting.     

Fungi associated with Collembola and mites isolated from scabby potatoes

Collembola and mites from the lesions of tubers infected with the acid scab organism were tested for the presence of fungal potato pathogens.Streptomyces spp. were found on and in the bodies of these arthropods.Verticillium albo-atrum was present on the external surface and in the body of the Collembola. Various other soil-inhabiting fungi which are not known to be potato pathogens and which were found on and in the bodies of these arthropods are noted.     

A method for large scale laboratory inoculation of potato tubers with late blight fungus

As part of a project to investigate the possibility that teratogenic factors are formed in potato tubers infected with the late blight fungus,Phytophthora infestans, a method was devised which allowed quick, efficient inoculation of large numbers of potato tubers. Tubers were placed in specially constructed trays, wounded by puncturing the periderm with flower “pin frogs”, and sprayed with a zoospore suspensionof P. infestans prepared from cultures grown on rye agar at 20C (68F) for 10 days. Approximately 95% of Katahdin and 93% of Russet Sebago tubers inoculated by this method exhibited typical late blight lesions after two weeks incubation at 20C, 80–90% RH. Eight tons of potatoes were processed in this manner.     

Correlation of phytotoxin production with pathogenicity ofStreptomyces scabies isolates from scab infected potato tubers

A total of 23 isolates obtained from scab infected potato tubers representative of six sampling areas in Eastern and Central Canada and five ATCCStreptomyces strains were screened for pathogenicity on the basis of their ability to initiate scab development on aseptically cultured minitubers and plant generated tubers. The results were then correlated with any associated generation of the scab inducing phytotoxin, Thaxtomin A. In all cases a positive correlation was demonstrated between the pathogenicity of variousStreptomyces scabies isolates and their ability to produce the phytotoxin.     

The effect of some vine desiccants on periderm development on cut potato tuber pieces

Russet Burbank, Red Pontiac, and Superior potato plants were treated with vine desiccants at the rate of 0.50 kg/ha and 1.12 kg/ha paraquat + X77, diquat + X77 and 2.24 kg/ha of Dow General, alone and with Crop Oil, 2 to 4 weeks before harvest. Untreated and treated tubers were selected for anatomical examination directly after harvest and after 22 weeks of storage. The tubers were cut in half longitudinally and exposed to optimum environmental conditions for 25 days when they were examined for periderm formation. Wound periderm in untreated tubers consisted of uniformly shaped and continuous layers of cambial cells. Tubers treated with 0.56 kg/ ha paraquat had a less developed periderm than untreated ones, but it would serve as a barrier against the invasion of pathogens. Diquat at the same concentration had fewer cambial cells and they were not continuous so that pathogen entrance was possible. With 1.12 kg/ha paraquat the periderm was less and with diquat more differentiated than the 0.56 kg/ha treatment indicating that concentration had some effect. Treatment with Dow General resulted in the formation of a periderm adequate for prevention of pathogen entrance. The effectiveness of the 3 chemicals to form periderm in Superior and Red Pontiac was similar to that of Russet Burbank. Periderm was most highly differentiated in untreated tubers followed by paraquat, Dow General, and diquat treated tubers.     

Influence of calcium on internal heat necrosis of Atlantic potato

While Atlantic is the cultivar of choice of potato chip processors for the mid-Atlantic region, susceptibility to internal heat necrosis (IHN) greatly increases grower risk of economic loss from unsalable tubers. Yield, tuber calcium levels, and percentage of tubers with IHN of several cultivars from a common seed source were examined at two locations. The percentage of tubers with IHN were significantly higher for Atlantic while the tuber Ca concentration was lower than those of Superior. Both the percentage of tubers with IHN and tuber Ca concentration was higher in New Jersey than Virginia. Lower Ca levels were found in tubers with necrotic medullary tissue than in those without. Studies were completed in Virginia and New Jersey to evaluate the influence of Ca source, Ca rate and location within the hill as well as nitrogen rate on the onset and progression of IHN of Atlantic potato. Tuber yield was not significantly influenced by either Ca source (calcium carbonate (CaCO₃) or calcium sulfate (CaSO₄)) or Ca rate (0-1800 kg Ca/ha). Calcium rate had no influence on size distribution. As expected, a significantly greater percentage of large tubers were noted with delayed harvest. In a short growing season (<110 days) yield was not influenced by nitrogen rates ranging from 84 to 252 kg/ha. However, with delayed harvest, yield was increased and IHN slightly reduced with 168 or 252 kg N/ha when compared to 84 kg/ha. The influence of applied Ca on IHN varied between years, but the addition of Ca or N did not reduce IHN sufficiently to avoid out-of-grade because of internal defects. Location of applied Ca within the hill had no effect on yield, specific gravity, IHN, or tissue Ca concentrations. Slightly higher leaf Ca was found when using CaCO₃ than CaSo₄. The influence of Ca rate in 1987 and 1988 on leaf, periderm, or medullary Ca concentrations was not consistent. Nitrogen had no significant influence on tissue Ca levels.     

A method for estimating the decrease in marketable tubers caused by potato late blight

A regression analysis was used to develop a method to estimate the decrease in marketable tubers caused by late blight of potato (Phytophthora infestans), based on estimates of percentage loss in total tuber yield computed from a published method. The economic loss due to late blight in table stocks is the relative percentage marketable yield loss, calculated from the expression: {fx19-01} when total yield losses (in percentage) did not exceed 40%. A graphical method is presented as an alternative. Yield results from seven field experiments conducted in the Maritime Provinces of Canada during the period 1953 to 1971 were used in the study, where marketable tubers were defined as 2 1/4 inch or more in diameter.