Shoot development and flowering in potato (Solanum tuberosum L.)

Summary The shoot system of potato is a configuration of stems with terminal inflorescences. In this review, shoot development is quantified in terms of stem production, while stem development is quantified in terms of leaf and flower primordia production per stem, which are functions of the rates and the durations of primordia initiation. The effect of the position of the stem in the shoot system on number of leaves and flowers per stem is also evaluated. Flowering of individual stems is described by the ‘time to flower primordia initiation’ (expressed in number of leaves produced) and ‘flower production’ (a function of the number and the development of flower primordia). At warmer temperatures and longer daylengths the number of leaves and flower primordia per stem, and the number of stems per shoot increase by prolonging stem production and primordia development. Temperature and photoperiod also affect flower primordia survival by altering assimilate production and partitioning. The photothermal response of the number of leaves per stem is small compared to the response of stem production; at higher temperatures, flower primordia survival becomes the principal factor determining flower production. The similarity of the signals leading to flower primordia initiation and tuberization, and the relation between shoot and tuber growth are discussed.     

Genotype X environment interactions in potato (Solanum tuberosum L.)

Genotype X environment interactions were estimated for several traits in potato from a combined analysis of 11 genotypes grown at 3 locations for 2 years. Genotype X location X year and Genotype X location interactions were significant for the majority of the traits studied. Yield, reducing sugar content, dry matter content, leaf area, plant height and starch content should be tested over multiple locations and years in order to separate the genotype × environment interaction components from the total genotypic variance.     

A rapid screening technique for drought resistance in potato (Solanum tuberosum L.)

Summary The reduction in growth in the dark of leaf dises floated over polyethylene glycol 6000 solution of water potential −0.4 MPa, relative to the growth of similar leaf dises floated over water for the same period, varied in the range 10–87% in 28 genotypes. The growth reductions in the genotypes tested were in general agreement with what is known about their drought resistance. Publication No. 906, Central Potato Research Institute, Simla.     

Optimizing the propagation of potato (Solanum tuberosum L.) by stem cuttings

Stem cuttings from potato plants are frequently used in multiplication programs for disease-free cultivars. The survival of these leafy cuttings is often very poor, and thus various techniques were investigated which were designed to increase rooting and cutting survival. Stock plants of cultivars “Caribe,” “Jemseg,” “Keswick,” “Russet Burbank,” “Sable,” “Sebago” and “Shepody” were grown in the greenhouse under long days. Promoting growth of the axillary shoots was successfully achieved by shading the shoot apex with aluminum foil. Trimming the outer leaves of the cuttings was deleterious to both survival and rooting. A rooting hormone improved root initiation and development, and the use of shade cloth or intermittent mist increased survival by reducing wilting. A rooting substrate of vermiculite: perlite (1:1) provided sufficient aeration, support and drainage for the cuttings. Antitranspirants sprayed on the stock plants prior to the excision of cuttings and also on the excised cuttings did not improve rooting or survival. The addition of activated charcoal (1% w:w) increased rooting of the cuttings and improved vigor of potted plants obtained from the cuttings.     

Plant regeneration from cell suspension culture of potato (Solanum tuberosum L.)

In the present study, for callus production leaf and stem segments of potato cultivar White Desiree were cultured on MS medium supplemented with 2,4-D, NAA and Kinetin (callus production medium). Calli then were transferred in the same liquid medium for cell suspension production. In the next step cell suspensions were transferred back to the callus production medium. Finally, calli derived from cell suspension were cultured on 6 different shoot initiation media (S1-S6). However, on S6 medium with combination of GA3 and BAP more than 80% of the calli produced shoot buds and shoots. Fully grown shoots then were rooted and produced whole plants. Chromosome and morphological analysis showed no somaclonal variation among regenerated plants.     

Suppression of marker genes in sequentially transformed potato (Solanum tuberosum L.)

Transgenic potato lines were developed from the advanced selection, ND860-2, by sequential transformation usingAgrobacterium tumefaciens and two different constructs. Five doubly-transformed lines were utilized to study gene expression of the first construct. Three doubly-transformed lines had less NPT II antigen than the singly-transformed counterpart from which each was derived. GUS activity was reduced in all doubly-transformed lines compared to their singly-transformed original genotypes. Therefore, NPT II and GUS genes in the first construct were suppressed to varying degrees by a second construct. Further investigations into this important subject will be necessary to enable multiple transformations with genes of agronomic interest.     

Effects of exogenous applications of cytokinin on the development of potato (Solanum tuberosum L.) cuttings

Summary Application of 6-benzylaminopurine or its riboside to potato cuttings on four successive days was very effective if the treatment started on day 4 after cutting. These cytokinis caused cuttings that were well induced to express a lower level of induction than they actually had received. There was a shift from sessile tuberization of the central bud to non-sessile tuberization of the central bud or to tuberization of ancillary buds, or a shift from ancillary-bud tuberization to swollen shoots. Effects were largest after a moderate induction. If rooting occurred, cytokinin reduced the proportion of rooted cuttings significantly. Cytokinin increased the levels of fructose and glucose in the tubers if it was applied after day 3. Dry weight of the buds was reduced by cytokinin in those cases where it caused suppression of ancillary-bud development. Paper No 836, Department of Vegetable Crops, Cornell University, Ithaca, N.Y. 14853, USA.     

Effects of growth regulators on the growth and yield of detached and transplanted potato (Solanum tuberosum L.) sprouts

Summary Roots of 15-day-old sprouts detached from tubers of potato (Solanum tuberosum L.) cv., Local Red, were dipped for 1 min in a 0.25% solution of Ethrel (ethephon), Rootone-F (RF), or Transplantone (TP) or in water and then planted in the field. Plants treated with RF and TP were significantly (P<0.05) taller, had heavier haulm, produced more leaves, and yielded more tubers than those of the control treatment with water, ethephon had no effect. RF was significantly (P<0.05) superior to TP for all measured components except leaf number.     

Unsaponifiable lipids from haulm and tuber sprouts of potato (Solanum tuberosum L.)

Summary Fractions containing Δ⁵- and Δ⁷-sterols, 4-methyl-sterols, triterpenic alcohols, tocopherols and hydrocarbons were isolated by TLC from petroleum ether extracts of the haulm and tuber sprouts of cv Désirée. Sterol and triterpenic alcohol fractions of unsaponifiable lipids of the haulm and tuber sprouts were found to contain twelve sterols and four triterpenic alcohols, respectively. 24R-4-stigmasten-3-on, Δ⁷, Δ⁷, lanosterol, cycloeucalenol and obtisufoliol have not been identified previously in unsaponifiable lipids from haulm and sprouts. In the hydrocarbon fractions of the haulm extract, C₂₃-to C₃₃-n-parafins, C₁₉-and C₃₁-cyclohexyl hydrocarbons, C₂₂-to C₃₈-olefins and squalene were identified, and in the hydrocarbon fractions of the tuber sprouts C₁₂-to C₂₆-olefins and squalene were identified.     

Water relations of the potato (Solanum tuberosum L.) cultivars Raritan and Shepody

Physiological responses to drought stress were evaluated in the potato cultivars Raritan and Shepody. Under well-watered conditions, Raritan exhibited a higher transpiration rate than Shepody. This higher rate could be related to a lower calculated stomatal resistance on abaxial leaf surfaces. Under drought stress conditions, Raritan consistently demonstrated superior performance over Shepody in the following areas: leaf water retention, epicuticular wax levels, desiccation tolerance and root growth. The estimated relative water content at a leaf water potential of-1.0 MPa was higher for Raritan than Shepody regardless of leaf age and may indicate a greater drought resistance in the former cultivar.     

Changes in ascorbic acid content during growth and short-term storage of potato tubers (Solanum tuberosum L.)

Changes in ascorbic acid levels were followed in apical and basal portions of Russet Burbank and Kennebec tubers during growth and development. Influence of nitrogen fertilization during growth and short-term storage on ascorbic acid level of the tuber was also studied. Changes in ascorbic acid content during growth showed two distinct phases, the first phase being characterized by an increase in ascorbic acid content with growth and development of the tuber, followed by a second phase which showed a decrease in ascorbic acid content with increasing maturity. The shift from the first phase to the second phase occurred earlier for Kennebec than for Russet Burbank. Increased nitrogen fertilization resulted in a delay of this shift from the first to the second phase. The apical portion of the tuber consistently showed higher ascorbic acid content than the basal portion. Kennebec tubers were higher in vitamin C content than tubers of Russet Burbank cultivar. High nitrogen fertilization resulted in less ascorbic acid content during growth. Storage of tubers for four weeks at 5.5°C also resulted in a marked decrease in ascorbic acid content of tubers. Nitrogen fertilizer rate during growth had no influence on the decrease in ascorbic acid content of tubers in storage.     

Cryopreservation of in vitro-grown meristems of potato (Solanum tuberosum L.) by encapsulation-vitrification

Summary Alginate coated meristems from in vitro-grown axillary buds of potato (Solanum tuberosum L.) were successfully cryopreserved by vitrification. Excised meristems were precultured on sucrose-enriched MS medium and then encapsulated. To induce dehydration tolerance (osmotolerance), encapsulated meristems were treated with a mixture of 2 M glycerol plus 0.6 M sucrose for 90 min. These encapsulated meristems were dehydrated with a highly concentrated vitrification solution (PVS2 solution) for 3 hr at 0°C prior to a plunge into liquid nitrogen. Successfully vitrified meristems developed shoots within 3 weeks after plating without intermediary callus formation. The average rate of shoot formation amounted to nearly 70%. No difference was observed in RAPD analysis using 17 primers between cryopreserved and non-treated plantlets. The cryogenic protocol was successfully applied to 14 cultivars. It was also confirmed that the encapsulated vitrified meristems produced much greater shoot formation than the encapsulated dried meristems. Thus, the encapsulation vitrification protocol appears promising for cryopreservation of potato germplasm.     

Isolation of solanidine from haulm and tuber sprouts of potato (Solanum tuberosum L.)

Summary The kinetics of enzymatic transformation of total glycoalkaloids (TGA) in haulm and tuber sprouts of potato to solanidine and the kinetics of solanidine isolation from plant material were studied. The optimum reaction conditions for the enzymatic TGA transformation were found for haulm to be: plant material to liquid phase 1:4 w/v, temperature 35°C, pH 5.4; and for tuber sprouts: plant material to liquid phase 1:3 w/v, temperature 37°C, pH 5.4. The. maximum degree of enzymatic transformation of TGA in haulm and tuber sprouts of 65 and 75%, respectively, was achieved after 50h. Carbon tetrachloride was the best solvent for solanidine extraction from the plant materials. The optimum ratio of plant material to carbon tetrachloride for the isolation of solanidine was 1:8 w/v for both extraction cycles, ensuring a yield of solanidine of approximately 55 and 65% from haulm and tuber sprouts, respectively, after 30 min.     

Varietal and environmental effect on the glycoalkaloid content of potato (Solanum tuberosum L.)

The tubers of 14 potato varieties were analysed for glycoalkaloids. The level of glycoalkaloids in tubers of all the varieties analysed are within the safe limits for human consumption. The peels of tuber contained about 60–70% of the total glycoalkaloids present in the whole tuber. The levels of glycoalkaloids in leaves and tubers were correlated (r=0.865). There was a significant increase in the content of glycoalkaloids in peels of tubers exposed to sunlight. Glycoalkaloid contents increased at the rate of 1.9mg/100g fresh weight per day in peels of Kufri Jyoti tubers exposed to diffused sunlight.     

A Kunitz-type proteinase inhibitor with differential solubility during the development of potato (Solanum tuberosum L.) tubers

Summary Two potato (Solanum tuberosum L., cv. Irish Cobbler) Kunitz-type proteinase inhibitors (PKPI) were previously described to be present in the soluble fraction of proteins from tubers in the early stages of development. One of them became insoluble in mature tubers, being extractable from this material in presence of urea. Amino acid sequencing showed that the soluble and insoluble PKPI were identical to each other. Also, immunolocalization using the protein A-gold method showed that both proteins were present inside the vacuole in free (intravacuolar space) and aggregated forms. The density of PKPI in the vacuolar protein aggregates increased from developing to mature tubers. showing that the soluble-insoluble state of this protein is related to the aggregation levels. Purified PKPI precipitated in vitro. mainly in presence of high calcium concentrations and low pH, but this precipitated form was not as stable as aggregates found in vivo. Based on the results obtained, a model of PKPI insolubilization in vivo is discussed.     

High temperature storage of potato (Solanum tuberosum L.) for processing — a feasibility study

Tubers of three potato cultivars were stored at room temperature (20–39°C, 30–75% RH), under an insulated storage run on passive evaporative cooling (16–30°C, 70–90% RH) and a refrigerated storage (2–4°C, 90–95% RH) for 14 weeks and studied periodically for storage losses, reducing sugar content and dry matter percent of tubers, in order to explore the possibility of storing potatoes for processing at higher temperatures. Physiological losses in tubers remained less than 10% until 12 weeks of storage under evaporatively cooled storage. Reducing sugar contents increased by only 52.4–242.1% in tubers stored in evaporatively cooled storage as compared to 90.5–484.2% increase in tubers stored in refrigerated storage until 14 weeks. Potatoes stored in evaporatively cooled store were more suitable for processing into chips and french fries due to lower physiological losses and lower reducing sugar content of tubers.     

Effects of temperature and photoperiod on early growth and final number of tubers in potato (Solanum tuberosum L.)

Summary A phytotron experiment with all combinations of two photoperiod (12 or 18 h) and four temperature (18/12, 22/16, 26/20 or 30/24 °C; 12h/12h) treatments was carried out to analyse quantitative effects on early tuber growth, dry-matter partitioning and number of tubers of two cultivars. Higher temperatures and longer photoperiod delayed the onset of expolinear tuber growth and the onset of linear tuber bulking. Higher temperatures also gave lower absolute tuber growth rates. Photoperiod did not affect absolute tuber growth rate at lower temperatures. Higher temperature and longer photoperiod gave lower relative rates of partitioning of dry matter to the tubers. Differences between treatments in numbers of tubers initiated were inconsistent. This quantitative analysis of the effects of temperature and photoperiod on characteristics of tuber growth should prove useful in potato modelling.     

Characterization of a new gibberellin related dwarfing locus in potato (Solanum tuberosum L.)

Gibberellins have been shown to be involved in such important processes as seed germination, flowering, maturation and tuberization in potato. Parents fromSolanum tuberosum Groups Andigena and Tuberosum were found to produce progeny containing dark green, rosette dwarf individuals which could be completely restored to normal appearance by exogenous GA₃. Test crosses indicated that this phenomenon can be explained by the action of a single locus, the dwarfing characteristic being conferred by the nulliplex condition. The gene symbol “ga₁” is proposed. Group Andigena dwarfs demonstrated much greater tuberization compared to their normal full sibs or dwarfs restored to normal phenotype by exogenous GA₃. The possibility that such gibberellin mutants may be involved in the long day adaptation of Gp. Tuberosum is discussed. This character may also be a useful tool for investigating various aspects of the gibberellin status of the potato.