Comparison of methods for measuring leaf and tuber water potentials in potatoes

Comparative methods for measuring water potential in leaves and tubers of potatoes (Solarium tuberosum L., var. Russet Burbank) are described. For leaves drier than -3 bars, the pressure chamber gave estimates of water potential which were zero to three bars drier than potentials measured using thermocouple psychrometers. Pressure chamber readings ranged ±2.5 bars from psychrometer value for leaves wetter than -3 bars; the psychrometer measurement usually was drier than the pressure chamber when leaves were sampled in the evening. With tubers, water potential measurements usingin situ psychrometers and the pressure chamber agreed to within one bar,except in tubers drier than -7 bars, where there were discrepancies of± 2.5 bars. However, if the interval between psychrometer insertion and water potential measurement were longer than 24 hours, serious errors arose in the psychrometer measurements, apparently from suberization of tissues surrounding the psychrometers which prevented vapor equilibrium. Pressure chamber measurements of tubers also were compared with tuber water potentials determined from the weight changes of tuber samples immersed in graded sucrose osmotica. For tubers wetter than -5 bars, the osmotica method gave drier estimates than the pressure chamber; for tubers drier than -5 bars the reverse occurred. Causes for these discrepancies are discussed.     

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.     

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.     

Accumulation of dry matter and N,P, K,by Russet Burbank,Oromonte and Red McClure potatoes

Potato plants of Russet Burbank, Oromonte and Red McClure varieties were studied in the San Luis Valley of Colorado to determine their dry matter and nutrient accumulation. The following observations were made in the 1967 growing season.

1. Growth patterns for the three varieties were similar, but average growth rate of Oromonte and Red McClure was higher than that of Russet Burbank.
2. Top growth reached its peak in 61, 55, and 50 days after emergence for Russet Burbank, Oromonte and Red McClure, respectively.
3. In the 3 weeks before killing forst, tuber growth equalled 50% of maximum tuber dry weight for Russet Burbank and about 61% for Oromonte and Red McClure.
4. Total N uptake with a yield of 300 cwt per acre was about 127 lb for each variety, assuming a linear relationship between tuber yield and nitrogen uptake. The tubers contained about 71% of the total N uptake.
5. Total P uptake with a yield of 300 cwt per acre was about 16 1b for each variety, assuming a linear relationship between tuber yield and P uptake. The tubers contained about 83% of total P uptake.
6. Total K uptake with a yield of 300 cwt per acre was 132, 187, and 147 lb (not significantly different) for Russet Burbank, Oromonte and Red McClure, respectively, assuming a linear relationship between tuber yield and K uptake. The Russet Burbank tubers contained 63% of the total K uptake and Oromonte and Red McClure about 52%.
7. Tuber dry matter per cent increased during the season until 2 weeks before a killing frost (65 to 69 days after emergence). At harvest, the dry matter approximated 21% for the varieties studied.

     

Techniques for detecting and measuring developmental and maturational changes in tuber native periderm

We developed a technique to quantitate native periderm permeability during tuber growth and maturation by porometrically determining vapor conductances. We also describe a simple, inexpensive means of determining the corresponding weight per unit area of suberized phellem cells (skin) in native periderm during tuber growth and maturation as a means of assessing the developmental status of native periderm. The porometric technique is very sensitive and rapid. Porometrically derived vapor conductances of mature native periderms were measured without difficulty, and native periderms were found to release ~0.005 moles of water vapor/meter² native periderm surface/sec. into a dry test atmosphere. Immature native periderm released up to 28 times more water vapor than mature periderm even though the phellem cells were histochemically determined to possess both major components of suberin. We demonstrated use of the porometric technique by determining maturational changes in periderm permeability of growing/immature tubers and mature tubers at harvest. The technique revealed that the native periderm of Russet Burbank tubers was more permeable and had the potential to lose more water vapor, until becoming permeably mature, than Norchip or Norland tubers harvested on the same dates. The dry weight of the skin (phellem tissue) of native periderm (mg/ cm²) for all three cultivars increased during tuber growth, but plateaued to a relatively constant level, or slightly declined, while plants were still alive during the latter period of tuber growth. During this period, periderm vameable conductances were undergoing substantial declines. Comparison of skin dry weights of immature tubers indicated that stem end regions of tubers were developmentally ahead of equatorial and bud end regions; this difference decreased as the tubers matured at harvest time and was less apparent with some cultivars.     

Production and chemical composition of potatoes related to placement and rate of nitrogen

Experiments with 11 N rates were conducted 3 years with Kennebec potatoes on Bodenburg silt loam in the Matanuska Valley of Alaska. Fertilizer placed in the row was compared with that mixed with the soil in the row for 2 years. Foliage and tuber samples were analyzed for chemical content. Stand reduction and decreased vigor occurred when row placed N exceeded 120–160 1b per acre. Foliage dry matter decreased 2 years as rate of N increased. Tuber dry matter was decreased one year by N rates exceed ing 100 1b per acre. U. S. No. 1 yield and dry matter with row placement of fertilizers at 40–80 1b N were highest in 2 years. When fertilizer was mixed with soil, both US No. 1 and dry matter yields increased each year with each N increment through 160 1b per acre. Increasing amounts of N tended to increase the N in foliage and tubers, the Mn in foliage but to decrease the Ca, Mg, Al, Ba, and Sr in foliage. Mixing the fertilizer with the soil as compared to placement in the row increased the Ca, Mg, Al, Ba, Fe, and Sr in foliage, and the tuber uptake of N, K, Mg, and Sr and decreased foliage N. Alaskan potato growers have doubled or tripled their rate of application of fertilizer over the past 15 years. At digging time potato plants are usually green and some growers have felt these higher fertilizer rates were supplying an excess of N which was delaying tuber maturity and decreasing tuber quality.     

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.     

Potato leafroll virus purification and antiserum preparation for enzyme-linked immunosorbent assays

Potato leafroll virus (PLRV) was purified from potato foliage and stems with an average yield of 0.14 mg of PLRV/kg of potato. Modifications of an existing purification procedure are reported. Five low dosage (38-118 μg of PLRV) intravenous injections were used to produce a PLRV antiserum for use in enzyme-linked immunosorbent assays (ELISA) from tubers. PLRV was readily detected in ELISA testing of potato tubers and leaves and inPhysalis floridana Rybd. Non-specific reactions were low with all tissues. In parallel tests, a Canadian antiserum produced higher nonspecific reactions with tuber and leaf tissue. The results indicated that the use of low dosage-intravenous injections might be necessary methodology for producing PLRV antiserum for use in ELISA diagnostic tests with tuber tissue where high non-specific reactions have been reported.     

Some anatomical and physiological potato tuber characteristics and their relationship to hollow heart

The inception site of hollow heart (HH) and possible relationships between HH and physiological or anatomical characteristics of tubers were investigated. Scanning electron micrographs revealed cells at the site of HH inception were physically rather than enzymatically degraded. Transmission electron micrographs of tuber pith cells from non hollow (NH) tubers showed cell wall and cytoplasm width varied among cultivars but were not related to HH resistance. Water potential of NH tuber tissues at the pith, bud, center and stem end of 3 cultivars and one selection varying in resistance to HH was determined. Although the water potential gradually became less negative as tubers advanced in maturity, no differences were found in water potential between pith cells in various parts of tubers or among cultivars. Tuber pith cells increased in size concomitant with tuber growth. In all tubers pith cells were largest in the center and stem end and smallest in the bud end, but differences in mean pith cell size among cultivars were not related to HH susceptibility. However, within a cultivar the bud, center, and stem end pith cells of HH tubers were all smaller than the corresponding pith cells from similarly sized NH tubers.     

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.     

Dry-matter production,and nutrient uptake and removal bySolanum andigena in the Peruvian Andes

A Field experiment withSolanum andigena (cv. Renacimiento) at three levels of fertilization was conducted in the Mantaro Valley (Central Sierra) of Peru during the 1967–68 growing season. Dry matter and nutrient accumulation in tops and tubers of Renacimiento potatoes were determined at 3-week intervals between 72 and 172 days after planting (42 and 142 days after emergence). Tuber initiation took place during the interval 116–137 days after planting, and top growth reached its maximum shortly thereafter. Total growth rates of 200 kg/ha/day⁴ (178 lb/a/day) where estimated under medium and high fertilization, and tuber dry matter accounted for 70–75% of the total dry matter produced. Final tuber yields (fresh, 21% dry matter) ranged from 10m.t./ha (89 cwt/a) without fertilizer to 41 m.t/ha (366 cwt/a) when fertilized with 160 kg each of N, P₂O₅ and K₂O/ha (143 lb/a). Under high fertilization, total N, P, and K accumulation was estimated at 141, 19, and 403 kg/ha (126, 17 and 359 lb/a), respectively, with 77 kg (68 lb/a) of N, 14 kg (12 lb/a) of P, and 224 kg (200lb/a) of K being removed in the tubers.     

Inheritance of tuber traits from phureja in diploid phureja - Tuberosum hybrids

Heterosis and combining ability for tuber number, average tuber weight, and total yield were evaluated in Phureja - haploid Tuberosum diploid hybrids. Heterosis estimates suggest dominance for high tuber number and low average tuber weight in Phureja. Total yield of the hybrid population exceeded the high parent. The higher-yielding segment of hybrids had a significantly higher number of smaller tubers per plant. Breeding value could be improved by attaining high yield with a lower number of larger tubers per plant. General combining ability was the only significant source of variation for tuber number and average tuber weight indicating high heritability. Phenotypic recurrent selection should be an effective approach to manipulating these traits. General and specific combining ability were significant for total yield. Full exploitation of genetic variance for yield will require test-crossing.     

Calcium and magnesium distribution in potato tubers

The calcium present in the potato tuber is partially extractable by water and by dilute HCl. Either of these procedures may show higher calcium content than dry-ashing. A degree of fractionation of calcium can be obtained by extraction by 1N HCl, first at room temperature and then at 70 C. Wet-ashing yielded consistently higher results for calcium than dry ashing. Analysis for calcium and magnesium in potato pith and cortex were made by wet-ashing following total sampling. The cortex of the tuber was found to contain about half of the weight but from 2/3 to 4/5 of the tuber calcium. Cortex as used here indicates the tissue exterior to the vascular ring. Magnesium was distributed evenly on a tissue weight basis. Kennebec tubers grown in three different states differed substantially in calcium content but not in magnesium content. This difference was especially pronounced in the cortex. Dividing the pith into inner and outer regions revealed that calcium levels were nearly the same throughout the pith.     

Utilization of potatoes for life support systems in space: III. Productivity at successive harvest dates under 12-H and 24-H photoperiods

Potatoes are among several crops under consideration for use in controlled ecological life support systems (CELSS) being proposed for space colonies. Efficient crop production for such life support systems will require nearoptimal growing conditions with harvests taken when production per unit area per unit time is maximum. To determine this maximum for potato, cv. Norland plants were grown in walk-in growth rooms under 12-h and 24-h photoperiods at 16 C and harvested at 42,63, 84,105,126 and 148 days from planting. At 42 days, plants were encaged in wire fence cylinders with a cross-sectional area of 0.2 m². The dry weights (dwt) of tubers and of the entire plants increased under both photoperiods until the final harvest date (148 days), reaching 572 g tuber dwt and 704 g total dwt under 12-h, and 791 g tuber dwt and 972 g total dwt under 24-h. At a spacing of 0.2 m² per plant, the 148-day tuber production from plants under continuous light would equate to nearly 40t ha^-1 dry matter (200t fresh weight), approximately twice that of exceptionally high field yields. Tuber productivity (g m^-2 day^-1) under the 24-h photoperiod reached a maximum of 29.4 g dwt m^-2 day^-1 at 126 days, but continued to rise throughout the experiment under the 12-h photoperiod, reaching 19.5 g dwt m^-2 day^-1 at 148 days. With a productivity of 29.4 g tuber dwt m^-2 day^-1, approximately 25 m² would continuously provide the daily dietary energy requirements for one human.     

Some aspects of potato appearance and texture. III. Sampling tubers for cation analysis

Individual unpeeled Kennebec tubers were analyzed after being subdiviled in various ways for sampling. The individual portions were wetashed whith a nitric-perchloric mixture and three cations were determined by Atomic Absorption Spectrophotometry. Representative samples of the tubers could be obtained by using subsamples of a blend or by using two opposite sectors cut longitudinally where each sector comprised 1/16th of the tuber. The latter method gave the greatest uniformity among the subsamples. Magnesium was uniformly distributed in the tubers studied, while calcium and potassium were more concentrated in the area external to the vascular tissue and in the stem and the bud ends of the tubers. The inequality of calcium distribution was extremely great.     

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.     

Vine pulling as a means of top killing potatoes

Vine pulling as a means of top killing potatoes was evaluated by measuring tuber discolouration, desiccation of stems and leaves, stems missed and rerooted, and tubers exposed during pulling. Tuber discolouration ratings determined for potatoes that had been top killed in mid-August by chemical desiccant, rotobeating or vine pulling, remained low during the four-year study except in 1978 with the chemical desiccant. Machine pulling evaluations indicated effective vine kill to be rated at 89–99% for leaves and 79–98% for stems with several cultivars of potatoes. A number of stems rerooted which reduced the vine kill ratings.     

Stage of development of leaf and tuber tissue of the potato plant influences the titer of potato virus M

The enzyme-linked immunosorbent assay (ELISA) was adapted for the detection of potato virus M (PVM). Detectability of PVM was influenced by the stage of plant growth and that of the plant part assayed. In young potato plants, one week prior to flowering, PVM titer was relatively high (0.77 A_405nm units) in the basal leaves and barely detectable (0.09 A_{405 nm} units) in the top leaves. In mature plants, two weeks prior to harvesting, top leaves contained more virus (0.34 A_{405 nm} units) than middle (0.24 A_405nm units) or basal leaves (0.15 A_{405 nm} units). In rapidly growing tubers PVM content was higher (1.57 A_{405 nm} units) than that in fully grown tubers (0.71 A_405nm units) whereas the virus was not detectable in the mother tuber four weeks following planting. PVM was reliably detected when disks from intact leaves were substituted for leaf extracts as the test sample