Synchronization of tuber formation in potato grown in vitro by cell division synchronization in axillary meristems of stem explants

Optimization of in vitro tuberization (formation and growth of stolons and microtubers) by synchronization of cell divisions in axillary meristems of initial stem explants induced by low nonfreezing temperatures was studied in potato (Solanum tuberosum L., cv. Lugovskoi) plants. The proportion of simultaneously dividing cells in axillary meristems of stem explants subjected to 2-h cold treatment at 4°C was in 2.6 times greater than in control material (without chilling). The analysis of growth of stolons and microtubers produced from the explants exposed to cold showed that synchronization of cell divisions in the meristems of initial explants resulted in synchronization of stolon and microtuber formation and production of microtubers of identical physiological age.     

Jasmonate effects on in vitro tuberization and tuber bulking in two potato cultivars (Solanum tuberosum L.) under different media and photoperiod conditions

Summary Jasmonic acid (JA) effects on in vitro tuberization of potato nodal explants cvs. Sangre and Russet Burbank were tested under liquid and solid media conditions and 0,8, and 16h photoperiod. Explants taken from stock plants grown on 2.5μM JA-supplemented medium tuberized first, particularly in darkness. The most pronounced benefits of the JA pretreatment were recorded under 16h photoperiod, which is known to inhibit tuberization. Cultivar Sangre benefited from the JA preconditioning of stock plants more than Russet Burbank. Russet Burbank required the JA supplement in tuberization media to reach the same degree of stimulation. Overall, microtubers produced either from JA preconditioned stock plants or on the JA-containing tuberization media were more uniform and larger than from other treatments. Eight hours photoperiod was by far the best treatment for the production of high-quality uniform microtubers. JA conditioning of stock plants prior to taking explants for tuberization is being proposed as a treatment enhancing the quality of microtubers.     

Morphological control and mensuration of potato plantlets from tissue cultures for automated micropropagation

Automation in plant micropropagation can be greatly simplified if the propagated plantlets have some morphological properties that facilitate automatic chopping and subsequent inspection and classification of the pre-cut plantlet segments by machine vision as viable propagules. We were able to control the morphogenic pattern of in vitro-propagated potato plantlets by adding various concentrations of ancymidol to the nutrient solution. It was found that plantlets cultured in 0.25 mg l^–1 ancymidol best fit the requirements for automated mass micropropagation; the mean internode length was sufficiently large (9–10 mm), the color contrast between leaves and stems was significantly enhanced, the stem was thicker than in the control treatment and the number of axillary buds per plantlet was maximized. Microtuber formation on segments isolated from plants cultured in 0.25 and 0.5 mg l^–1 ancymidol media was enhanced shortly after transfer to tuber induction medium in vitro. On shoot segments from control plants, microtuber formation started after 24–28 days.Machine vision was used to evaluate the morphological and color changes in cultured potato plants. Geometrical and color features such as the number of buds, internode length and color contrast between leaf and stem were precisely measured and automatically logged. Features were measured that till now could only be observed qualitatively.Abbreviations F/W fresh weight - RGB red, green, blue principal color components - VTR video tape recorder     

Genotypic influence on in vitro induction, dormancy length, advancing age and agronomical performance of potato microtubers (Solanum tuberosum L.)

Microtubers of 13 cultivars, largely grown in Italy and other European countries, were induced. They were stored in the dark at 3°C for different periods (28, 56, 84 and 105 days), prior to being transferred to 20°C for between 4 and 17 weeks. Following removal to room temperature, sprouting was recorded and dormancy duration quantified. Dormancy decreased from 28.1 to 19.9, 11.1 and 7.8 days with reduced time of storage. Cvs Arsy, Nicola and Jaerla took consistently more time for dormancy release. The dormancy duration was linearly and inversely correlated with the length of storage. After sprouting, tubers were held at 20°C for various intervals and a range of physiological ages (0, 368, 720 and 1008 degree days) were accumulated. The field comparison of microtubers evidenced a plant growth response and tuber yield/plant affected by the cultivar and physiological age. In early cultivars (Jaerla), a better performance was shown by younger tubers; the opposite trend was noted in Alpha (a later cultivar) with an increase in stems/plant, tubers/plant and tuber yield/plant for tubers with greater physiological age. Like conventional seed tubers, microtubers showed differences in optimum physiological age associated with cultivar earliness. This study has provided some indications on how to enhance emergence and haulm development of plants from microtubers.     

Control of Dioscorea alata microtuber dormancy and germination by jasmonic acid

Effects of appling exogenous jasmonic acid (JA) on the germination of Dioscorea alata L. microtubers were examined on Murashige and Skoog (MS) medium. Microtuber germination was promoted by JA (0.1 and 1 M) supplemented to the culture medium but higher concentrations (30 and 100 M) completely inhibited germination. When these inhibited microtubers were transferred to hormone-free medium, germination resumed.After transfer to greenhouse conditions, almost all plants (95%) from tubers previously cultivated on MS medium with 100 M JA survived and all acclimatized plants had produced tubers after 8 months. It is concluded that depending on JA concentration, both the germination and dormancy processes in D. alata microtubers were affected. The release from dormancy is easily obtained by transferring dormant microtubers to hormone-free medium.     

Effects of activated charcoal effects on induction and development of microtubers in potato (Solanurn tuberosum L.)

The aim of this research was to compare hormone-free medium with media with regulator substances (activated charcoal, cytokinins, polyamine biosynthesis inhibitor and chlorocholine chloride) used for microtuber induction and development. Explants of cvs Monalisa, Primura and Spunta were multiplied subculturing nodal segments on plant growth regulator-free Murashige & Skoog (1962) (MS) medium. When the plantlets had 6–8 nodes, single-node stem segments were excised and transferred to eight tuberisation media, each consisting of MS basal components supplemented with sucrose (8% w/v) and various regulator substances. The control was a regulator-free medium including only sucrose. Results were expressed as the number and weight of microtubers per nodal explant.
The cultivars showed wide variations in the mean weight of microtubers, ranging from 44.6 mg (Primura) to 77.5 mg (Spunta), and nearly all plants produced tubers. Medium containing activated charcoal gave the highest rate of tuberisation and the largest microtubers. It thus played a role in optimising conditions for rapid, mass tuberisation of these cultivars, and produced large microtubers for field planting.     

Effects of photoperiod,mineral medium strength,inorganic ammonium,sucrose and cytokinin on root,shoot and microtuber development in shoot cultures of Dioscorea alata L. and D. bulbifera L. yams

The effects of photoperiod (8, 12 or 16 h), mineral medium strength (dilutions of a tuberization medium, the T medium), sucrose (0, 2, 4, 8% w/v) and kinetin (0, 2.5μM) on the development of roots, shoots and microtubers in shoot cultures of Dioscorea alata L. and D. bulbifera L. yams were evaluated. All of the factors were found to have substantial effects on microtuber induction in these two species. The effects of high and low inorganic ammonium containing media on microtuberization of yam shoot cultures indicated that ammonium ions inhibited microtuber induction in D. alata but not in D. bulbifera. Microtubers of D. alata were only formed on shoot cultures if these were held under 8-h days. D. bulbifera cultures on the other hand produced microtubers under this photoperiod treatment as well as under 16-h photoperiods provided that kinetin was present in media at 2.5μM. Most microtuberization in D. alata shoot cultures occurred on full-strength T medium supplemented with 2% sucrose, 2.5μM kinetin held under 8-h photoperiod at 25°C, whereas most microtuberization in D. bulbifera shoot cultures occurred on full-strength MS medium supplemented with 4% sucrose, 2.5μM kinetin held under 8-h photoperiods at 25°C. Under these two sets of conditions, yam shoot cultures consistently produced microtubers with individual weights in excess of 100 mg which were large enough to be capable of direct planting and subsequent growth in unsterilized soils.