Manipulation of microtubers for direct field utilization in seed production

A two-year field study was conducted to determine the effects of jasmonic acid (JA), light (duringin vitro explant production andin vitro tuberization phases), and dormancy-breaking treatment on performance of microtubers in the production of seed tubers (pre-elite) in five potato cultivars. Microtubers were produced under short day (8-h) conditions and in darkness, from stock plantlets pre-treated with JA and untreated, and on tuberization media with or without JA. Microtuber performance was compared to invitro plantlets transplanted directly to the field. Yields of tubers from microtubers were 30% to 40% of those from plantlets. Microtubers of cultivars Amisk and Russet Burbank produced the highest yields of pre-elite tubers. Atlantic microtubers performed poorly in the field. JA pre-treatment of stock plantlets, prior toin vitro tuberization, enhanced seeds tuber production from microtubers in Russet Burbank and lowered in Shepody. JA presence in media duringin vitro tuberization significantly lowered production of tubers while exposure to 8-h light resulted in microtubers performing significantly better in the field than microtubers produced in the dark. Dormancy release was the key factor influencing microtuber performance. Unlike greenhouse studies, gibberellic acid (GA₃) was more effective than Rindite. A further refinement of the production and handling methods is required before microtubers can be recommended for field production of seed tubers.     

Use of jasmonate for conditioning of potato plantlets and microtubers in greenhouse production of minitubers

A two-year study was conducted to determine the effects of (1) jasmonic acid (JA) pre-treatment, (2) JA supplement in culture media, (3) cultivar (Amisk, Atlantic, Russet Burbank, Shepody, and Umatilla Russet), (4) light (0 h, 8 h), and (5) dormancy breaking treatment (Rindite, gibberellic acid) on greenhouse production of minitubers from microtubers andin vitro plantlets. The microtubers were produced under short day (8 h) light conditions and in darkness, from stock plantlets pre-treated with JA and untreated, and on tuberization media with or without JA.In vitro plantlets (the industry choice in nuclear seed potato production) of all five cultivars performed well, meeting the standard criteria for greenhouse production of minitubers. Production of minitubers from microtuber-derived plants of cvs Amisk, Russet Burbank, and Umatilla Russet was similar to that of plantlet-derived plants with regard to number of minitubers. Yields (weight), however, were lower than those from plantlets. Microtuber responses to JA varied with cultivar. Amisk produced the highest number of minitubers per plot from microtubers derived from JA pre-treated plantlets. Jasmonic acid-pretreated microtubers also gave significantly more minitubers in Russet Burbank and Umatilla Russet than the microtubers from other treatments. Shepody did not benefit from JA treatments and JA pre-treated Atlantic microtubers performed poorly, producing significantly lower yields of minitubers than other cultivars. Independently of cultivar, microtubers produced under 8-h photoperiod gave significantly higher yields of minitubers than microtubers produced in the dark. Dormancy release was the key factor influencing microtuber performance. Rindite proved to be a much more effective dormancy breaking treatment than gibberellin. JA conditioning of stock plants prior to tuberization is being proposed as a treatment in production of microtubers for greenhouse production of minitubers.     

Jasmonate effect on in vitro tuberization of potato (Solanum tuberosum L.) cultivars under light and dark conditions

Summary Effects of jasmonic acid (JA) on in vitro tuberization of six potato cultivars were examined. Tuberization was carried out in the dark, or with 8 h photoperiod on MS media with vitamins, 8% sucrose, 0.6% agar and either 2.5 μM JA (JAMed) or no JA using explants either preconditioned with 2.5 μM JA (JAPret) or not. Cultivars Amisk, Russet Burbank, Sangre and Umatilla Russet produced the most (1.0–1.7) and the largest microtubers per explant. Tuberization was inconsistent in Shepody and poor in Atlantic. All cultivars tuberized significantly better in 8 h than in the dark. JA effects were cultivar specific and larger in the dark than in light. In the dark, Amisk, Atlantic and Umatila Russet tuberized better in JAMed than in JAPret. These cultivars did not benefit from JA treatments in light. Russet Burbank and Sangre tuberized in the dark better from JAPret cuttings than on JAMed medium. JA had no effect on tuberization in Shepody. JA double treatment in light vs. control and individual JA treatments significantly reduced tuberization in Shepody and Russet Burbank.     

The effect of the inhibitors of protein and nucleic acid synthesis on the coumarin-induced tuberization and growth of excised axillary shoots of potato sprquts (Solanum tuberosum l.) culturedin vitro

The inhibitors of protein and nucleic acid synthesis; chloramphenicol, para-fluorophenylalanine, actinomycin D, and 5-fluorouracil were evaluated for their effectiveness in inhibiting coumarin-induced tuberization, tuber growth, and the inhibition of.root and shoot growth of excised axillary shoots of potato sprouts culturedin vitro. To date, it has been demonstrated that both kinetin and coumarin readily effect 100 percent tuberization of the shoots culturedin vitro. The results of the present study demonstrate that with the exception of 5-fluorouracil, the inhibitors significantly inhibited the coumarin-induced. tuberization, tuber growth, and root growth whereas in previously published data by Palmer and Smith (6), the inhibitors merely delayed kinetin-induced tuberization. It is suggested that both protein and nucleic acid synthesis are required for the coumarin-induced tuberization processes, and the mode of action of coumarin is distinctly different from that of kinetin.     

General characteristics of coumarin-induced tuberization of axillary shoots ofSolanum tuberosum L. culturedin vitro

Coumarin readily stimulates tuberization of cultured axillary shoots obtained from etiolated potato sprouts. Adequate concentrations of coumarin must be continuously present in the medium to effect tuber initiation. High nitrogen, gibberellic acid, abscisic acid, indole acetic acid, or naphthalene acetic acid reduced or inhibited coumarin-induced tuberization. Gibberellic acid and high concentrations of nitrogen in medium inhibited the uptake of coumarin-3-14C by the. axillary shoot. Based on the data of physiological activities by coumarin in other plant species and our data on tuberization, we propose that coumarin may represent in part the unknown inhibitor responsible for tuber initiation with reference to the inhibitor/gibberellic acid ratio theory of tuberization.     

Effect of leaves on microtubers produced from potato single-node cuttingsIn Vitro

Microtubers are used to propagate, to store, and to transport potato clones. Culturing single-node explants from potato plantletsin vitro without subtending leaves was reported to result in plantlets with lower vigor and a higher coefficient of variation. The effect on microtuber productionin vitro of leaf area and the presence or absence of leaves on potato single-node cuttings was investigated as an extension of the above study. Stock plantlets of potato cvs Atlantic, Kennebec, Russet Burbank, and Shepody were cultured under a 16-h photoperiod. Single-node cuttings were excised and grown in a high-sucrose tuberization medium in darkness. Leaf area did not affect the frequency, size, or weight of microtubers of cvs Katahdin and Russet Burbank. The absence of leaves reduced microtuber diameter for Russet Burbank; whereas Atlantic, Kennebec, and Shepody were unaffected. Mean fresh weight of microtubers was reduced when leaves were removed for all cvs except Atlantic. No effect of the removal of the leaf was observed for mean dry weights of microtubers from all cvs, although microtubers from single-node cuttings without leaves accumulated significantly more percent dry matter than those with leaves. Rapid multiplication facilities may therefore wish to consider conserving resources such as media, vessels, and growth room space by culturing explants without leaves for the production of microtubers.     

Plant regeneration from tuber discs of potato (Solanum tuberosum L.) using 6-benzylaminopurine (BAP)

Summary Shoots, roots and callus were formed from tuber discs of potato, cultivar Désirée, when grown in vitro on the basal medium of Murashige & Skoog (1962) (MS) supplemented with 2,4-D and/or BAP. Callus was formed in MS medium with 1 mg l⁻¹ BAP plus 0.5 mg l⁻¹ 2,4-D, callus and roots were formed in MS with 1 mg l⁻¹ BAP plus more than 0.5 mg l⁻¹ 2,4-D and shoots were formed directly on tuber discs cultured on MS medium with 1 mg l⁻¹ BAP without the addition of 2,4-D. Nodules produced at the explant surface after the 4th week increased in size following subculture onto the same medium (MS+BAP alone), and 2 to 6 shoots developed from each nodule. After 9 weeks total time in culture, these shoots were excised and transferred as cuttings to MS medium without growth regulators, after which roots developed and plantlets were formed. A histological study of the explants at the sites of nodule formation indicated that the shoots developed from meristematic zones initiated within small outgrowths of tissue similar to those occuring in adventive organogenesis but the presence of shoot and root meristems associated with the same axis suggests the formation of somatic embryos.     

Extreme resistance to infection by potato virus X in genotypes of wild tuber-bearingSolanum species

Summary Clones derived from thirty-one different accessions (nineteen of Argentine origin) belonging to eightSolanum species were screened for resistance to infection by potato virus X strain cp (PVX cp) by mechanical inoculation of plantlets that had been micropropagated in vitro. Estimates of PVX multiplication obtained by enzyme linked immunosorbent assay and slot blot nucleic acid hybridization allowed the identification of resistant clones derived from five accessions belonging toS. commersonii S. oplocense, S. sparsipilum andS. tuberosum andigena. Resistant genotypes supported PVX concentrations 5 to 15 times smaller than did the susceptible control cultivar Spunta. Graft inoculation test confirmed the presence of extreme resistance similar to that conferred by the ‘immunity’ gene X¹ (also called RX_act).     

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.     

Light effects on the growth and morphogenesis of potato(Solanum tuberosum) in vitro: A review

Growth, morphogenesis, and tuberization of potato tissuesin vitro are affected by light. Measurements of the various aspects of light that control development and growth of potato are outlined. Physical parameters like light sources, delivery of the light source, and the degradation of culture media by light are discussed. Irradiance, photoautotrophic growthin vitro, spectral wavelength, and photoperiod modify the responses of potato tissues in culture. Acclimatization of tissue culture plantlets, vegetative growth, and the production, quality, and dormancy of microtubers are modified by light. New light sources such as light-emitting diode (LED) lamps are becoming available forin vitro research and for micropropagation of potato. Pulsed or chopper light has the potential to save energy costs. Light effects on potato protoplasts, anther culture, virus eradication, andin vitro conservation are discussed. Potential new research areas are the effect of the spectral quality of light on regeneration of shoots and somatic embryosin vitro, end-of-day red and far-red light treatments, axillary shoot formation in cultured plantlets, and the use of LEDs. The influence of monochromatic spectral filters on growth and development of potatoes in tissue culture could potentially lead to improvements in productivity. The relationship between daily quantum light integral and photoperiod and their effects on growth and morphogenesis of the potato will provide some useful areas of research.     

Tuberization in potato at high temperatures: Responses to exogenous gibberellin,cytokinin and ethylene

Summary In potato (Solanum tuberosum L., cv. Sebago), benzyladenine (BA) promoted tuberization at high day/night temperatures (32°/18°C), while gibberrellic acid (GA) and chlorethylphosphonic acid (CEPA) reduced tuberization at low day/night temperatures (22°/18°C). These results are consistent with the hypothesis that temperature exerts its influence on tuber formation by altering the balance between endogenous gibberellins, cytokinins and inhibitors, but not ethylene.     

A plant growth promoting rhizobacterium and temperature effects on performance of 18 clones of potato

A survey of genotypic responses to beneficial bacterium (Pseudomonas sp. strain PsJN) was conductedin vitro andex vitro, under two temperature conditions, using eighteen clones of potato of different heat stress tolerance: temperate adapted cultivars Kennebec and Russet Burbank; heat tolerant DTO-2, DTO-28, DTO-33, LT-1, LT-2, LT-5, LT-6, LT-7, LT-8, LT-9, Y84-02, NDD277-2, Désirée, and Maine-47; and heat sensitive abscissic acid (ABA)-deficient mutants 11401-01 and 9120-05. Nodal explants taken from 6-week-old bacterized and non-bacterized control plantlets were culturedin vitro on a hormone-free potato nodal cutting medium, and placed at either 20/15 C or 33/25 C day/night temperature, 12h photoperiod and 250 µE m^?2 s^?1 mixture of fluorescent and incandescent light, for six weeks. The tuberization response was studiedex vitro after two weeks acclimation of 2-week old plantlets at 33/25C. The acclimated plantlets were transplanted to 3L plastic nursery pots containing peat-based Pro-Mix growing medium and placed in growth chambers at either 20/15 or 33/25 C day/night temperature, 12 h photoperiod, 475 μE m^?2 s^?1 light and ≈80% RH, for 12 weeks. Compared to the non-bacterized controls, bacterization significantly increased stem length of 12, shoot biomass of 9, and root biomass of 2 clones at 20/15C; and stem length of 14, shoot biomass of 15, and root biomass of 13 clones at 33/25C. High temperature increased length of internodes and had either no effect or slightly decreased node number. Temperature increase had the most dramatic effect on root development. An average shoot to root ratio decreased from 3.7 at 20/15 C to 1.7 at 33/25 C for non-bacterized plantlets and, respectively, from 4.3 to 1.5 for bacterized. The beneficial effect of bacterization on root biomass was the most pronounced in LT-1 and Maine-47 at 20/15 C and LT-8, Maine 47, DTO-2, Kennebec, NDD277-2 and 11401-01 at 33/25C. The temperature elevation did not significantly affect root biomass of LT-6, DTO-28 and Désirée. Temperature stress caused severe reduction in tuber number and tuber fresh weight. ABA-deficient mutants did not produce any tubers and LT-8, LT-9, Y84-027 and DTO-28 tuberized very poorly at 33/25C. DTO-33, Désirée, LT-1 and Kennebec gave the highest number of tubers per pot and Kennebec, LT-1, Désirée and LT-7 the highest yields at this temperature. There was no significant effect of bacterization on tuberization at 20/15 C but at 33/25 C bacterization significantly enhanced tuber number and weight in LT-7 and reduced tuber weight in DTO-2. Although there was no clear link between thein vitro response of particular clones to bacterization and their heat stress tolerance, improvement ofex vitro performance of heat tolerant LT-7 indicates that rhizosphere bacteria may play a role in clonal adaptation of potato to heat stress.     

Hydroxylated jasmonate levels during stolon to tuber transition inSolarium tuberosum L

Summary Various octadecanoids and derived compounds have been identified in potato leaves. However, information regarding jasmonate hydroxylated forms in stolons or tubers is scarce. We investigated endogenous jasmonates in stolon material ofSolarium tuberosum cv. Spunta. Stolons and incipient tubers were collected from 8 weeks old plants. The material was cut into apical regions and stolons. We identified jasmonic acid (JA), methyl jasmonate, 11-OH-JA, 12-OH-JA, 12-oxo-phytodienoic acid (OPDA) and a conjugate. The content of JA and 12OH-JA decreased in the apical region but remained high in stolons during tuberization. Thus the apical region might be a site of JAs-utilization or metabolization and stolons might supply JAs to that region. The content of 12-OH-JA was higher than that of 11-OH-JA in all stages analyzed, both in apical regions and stolons. However, these compounds showed a different time-course in the apical region: while 11-OH-JA increased, 12-OH-JA decreased. Thus, JA from leaves or roots could be transported as 12-OH-JA to the apical region, stimulating tuber formation.     

The effect of nitrogen on the coumarin-induced tuberization of potato axillary shoots culturedin vitro

Coumarin-induced tuberization was studied on axillary shoots excised from etiolated potato sprouts each of which was cultured in vitro. Sprouts grown on culture medium with high nitrogen concentrations produced axillary shoots which elongated and would not readily tuberize. Sprouts cultured on medium low in nitrogen produced axillary shoots which tuberized with limited elongation. Carbohydrate concentration of the culture medium for the excised axillary shoot could significantly modify the nitrogen effect of the potato sprout medium. Axillary shoots growing on high nitrogen medium did not tuberize except in cases where the carbohydrate concentration was increased.     

The effect of boron on calcium uptake and growth in micropropagated potato plantlets

Summary Boron (B) requirements differ widely among plant species and the concentration range between toxicity and deficiency is less for B than for any other nutrient. Excess B can adversely affect calcium (Ca) uptake and plant growth. Potato cvs Bintje and Norland plantlets were micropropagated on Murashige & Skoog (MS) nutrient medium, supplemented with 3 (MS control level) or 9 mM Ca, and a range of H₃BO₃ levels (0.025 to 0.300 mM B). Medium B levels of 0.100 and 0.300 mM decreased Ca content in leaves and shoots of cv. Norland, but not Bintje. Medium B level of 0.025 mM, which is 25% of the control MS level, enhanced Ca uptake in cv. Norland and did not compromise normal plantlet growth in either cultivar. This lower H₃BO₃ level (0.025 mM B), and a B-free gelling agent such as Gelrite, could be used for micropropagation of potato and possibly other species susceptible to Ca defifiency disorders.     

离体培养条件下植物生长物质对马铃薯块茎形成的影响

在全黑暗诱导结薯培养条件下,培养基（MS＋8．0％蔗糖）中添加5．0BA、5．0B9、500CCC或5．0BA＋500CCC（mg／L）对诱导马铃薯（cv．Mira）试管苗或其茎段结薯所需的时间,结薯率和结薯数量没有促进作用;它们虽能略微提高试管薯的平均鲜重,但与对照比较,此影响未达到显著水平（LSD0.05）。在16h／d光周期或8h／d光周期加暗期光间断诱导结薯培养条件下,无论培养基中蔗糖含量为2．0％或8．0％,外源添加2．0NAA、2．0ABA、5．0BA、5．0B9、500CCC或5．0BA＋500CCC（mg／L）等植物生长物质均不能诱导试管苗茎段结薯（cv．I－1085）。由此表明,离体培养条件下,外源添加上述植物生长物质不是诱导马铃薯块茎形成的必需因子。对此试验结果作了比较详细的讨论。     

Potato leafroll virus distribution in potato meristem tips and production of virus-free plants

Summary Uridine-H³ was incorporated into meristem tips of both healthy and PLRV-infected potato plants, of the cultivars, Majestic and Primura. Autoradiograms of tips pretreated with actinomycin D showed that 13 of 14 and 11 of 14 respectively, were virus free in the dome and first 4 leaf primordia, 1 and 3 were infected in the 4th leaf primordium, and 1 of Primura also in its 3rd primordium. The highest plantlet yield from cultures in vitro of meristem tips that included 4 leaf primordia (7 to 9 plantlets per meristem), was obtained by growing them in sequence on 3 sequential media, each based on Murashige and Skoog basic medium complemented with various hormones. The 2nd medium, containing benzylaminopurine (0.5 mg/l) and gibberellic acid (0.5 mg/l), elicited callus and the subsequent formation of adventitious buds. Of the plantlets of the cvs Vivaks, Primura and Majestic, 88, 91 and 100 %, respectively, were PLRV-free. Propagation in vitro, by the single-node cutting technique and tuberlet production, were successful.     

Tuberization in potato at high temperatures: response of physiologically young plants to disbudding and growth inhibitors

Summary In physiologically young plants (Solanum tuberosum L., cv. Sebago), abscisic acid (ABA) and chlorethyltrimethylammonium chloride (CCC) promoted tuberization at day/night temperatures of 32°/18°C, but not at 32°/28°C, in contrast to earlier experiments with physiologically old plants. Disbudding promoted tuberization at both temperatures. These results suggest that physiologically young plants have a greater capacity for increased gibberelling synthesis in the buds at high temperatures.     

Development of amylose-free (amf) monoploid potatoes as new basic material for mutation breeding in vitro

Summary For the induction and selection of double mutants with altered starch composition, a uniform (homohistont) amylose-free (amf) monoploid as basic plant is of vital importance. Therefore, newamf monoploids had to be developed via prickle pollination. And 26 monoploids were obtained which were screened in vitro for vigour, leaf size and for the percentage of monoploid cells. The number of monoploid cells was underestimated at about 28%. Seven vigorous monoploids were tested in vitro for tuberization capacity, which varied from 0 to 100%. After regeneration in vitro, 0 to 3.7 adventitious shoots per leaf explant were formed. The tuberization capacity of these shoots varied from 0 to 48. Twoamf monoploids were selected which were vigorous and tuberized well in vitro. They are the basis for the application of an in vitro mutation breeding protocol that should lead to the induction and selection of new starch mutants in potato.     

Influence of nitrogen supply on micropropagation and subsequent microtuberization of four potato cullwars

A medium containing low amounts of nitrogen (19–23 meq.l^?1) produced optimum results in micropropagation as revealed by the number of nodes, internode length, chlorophyll content, and leaf area of four potato cvs. belonging each to four different maturity groups. Decreasing amounts of nitrogen also increased chlorophyll content in all four cultivars tested. The NH ₄ ⁺ concentration did not have an effect on micropropagation for low nitrogen supplies. In all cvs., except Baraka, there was a “carry over” effect of the nitrogen content in the micropropagation medium onto subsequent tuberization, the lower nitrogen (23 meq.l^?1) advancing tuber initiation. Microtuberization of cv. Jaerla was earlier in darkness than under short days regardless of the propagation medium used.