The influence of temperature, period and mode of storage of Gerbera propagated in vitro on the quality of stored material.

by Teresa Hempel and Maciej Hempel

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Originally published in: Prace Instytutu Sadownictwa i Kwiaciarstwa, seria B, tom 10, 1985, pp.85-90

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Plant propagation in vitro enables the mass-production of any species or cultivar in the pre-planned season. Many micropropagation companies specialise in particular products and produce in excess of a million plants per year. Demand for planting material is usually seasonal which place big stress on laboratories and lower their turnover capacities. The only solution to this problem is to extend preparation of tissue culture products for a longer period of time. In countries with developed trade exchange, plants are produced out-of-season for export to countries with different climatic conditions. In countries with restricted trade contacts, the only solution is rooting plants out-of-season and storing them until sale or planting in a greenhouse.

Most papers on the subject deal with the possibilities of long-term storage in super-low temperature and gene banks. On the other hand, there are not many papers related to the storage of plant tissues for a few weeks or months in temperatures a little over 0°C. There are some references on storage of cultured gerbera tissues (Pierik et al., 1979; Maia and Bettachini, 1977), carnation (Hoof, 1980; Earle and Langhans, 1975), geranium (Reuther, 1983), chrysanthemum (Roest and Bokelmann, 1976), and apple (Lundergan and Janick, 1979). However, the authors of these papers did not analyze the direct or indirect influence of storage on the quality of produced plants.

Gerbera is one of the most important cut flower crops in Poland, and also the main crop in tissue culture production. Its share of the total in vitro production in Poland amounted to about 90% in 1984. The gerbera planting season lasts only two months - June and July. The storage of in vitro rooted plants could enable better exploitation of equipment and labour in laboratories, and , therefore improve their economical results.

In the papers concerning gerbera are remarks that it can be stored for a few months in temperature of 5°C (Maia and Bettachini, 1977; Pierik et. al., 1979). In the papers concerning other species the authors stated that tissue cultured shoots can be stored at 1°C (Lungergan and Janick, 1979), 2°C (Roest and Bokelmann, 1976), 4°C (Lundergan and Janick, 1979; Earle and Langhans, 1975; Hoof, 1980) or 6°C (Reuther, 1983).

The following experiments comprise investigations on the influence of temperature, period and mode of storage on the quality of rooted gerbera plants directly after storage, and their growth after planting in a greenhouse.

Material and methods

Plants of gerbera cv. Marleen were produced by the standard micropropagation method (Murashige et al., 1974). After rooting, they were stored either in 250 ml conical flasks, in which they had been rooted, or removed from rooting flasks and placed in plastic boxes (7 x 10 x 5 cm).

Rooting flasks containing 40 ml of medium and 15 plants were covered with aluminium foil.

Plants taken out of the flasks were dipped in a solution of fungicides (Benlate 0.1% + Fongarid 0.05%) for 3 minutes and left on a filter paper until the water, which remained on the leaves, evaporated. Then 50 plants were placed in each box. The boxes were sealead with Parafilm and packed in plastic bags which were folded in order to prevent dessication.

The influence of temperature (1°C and 4°C) and time of storage (1, 2, 4, 8, and 12 weeks) in darkness was investigated. At the end of storage, the quality of plants had been evaluated, they were planted in 6 cm pots containing the standard gerbera potting mixture and placed on a bench in a greenhouse. The bench was covered with plastic and a shadecloth. Plants were slowly acclimatized to greenhouse conditions according to the routine procedure for in vitro propagated material. They were fertilized and watered like average young gerbera plants.

The survival, height, branching, and dry weight of shoots and root system of 20 plants chosen randomly from each treatment were evaluated after 6 weeks of growth. The experiment was repeated 3 times. The statistical analysis of observed differences between treatments was conducted by Fisher's analysis of variance and Tuckey's multirange test at 5 % level of significance.

Results

The quality of plants stored in 4°C and in flasks was much better than the quality of plants stored in 1°C and in boxes. Dying of the root tips was observed. Root tips of the plants stored in boxes at 1°C started to die after 1 week of storage, while roots of plants kept at 4°C had been looking healthy until the 4th week of storage in flasks, when their root tips began to die. Root meristems of plants stored in flasks started to die after 4 and 12 weeks of storage in 1°C and 4°C, respectively. The necrosis of root tips did not directly effect the survival rate of transplanted plants.

The survival rate after planting in the greenhouse depended on temperature, period of storage and kind of vessel in which plants were stored (Table 1). Plants survived best when they were stored in rooting flasks at 4°C - about 95 % after 12 weeks of storage. However, if they were stored so long in the same kind of vessel or in boxes at 1°C, no plants survived transplanting. Differences in survival were not observed between plants which were not stored and plants stored at 4°C in flasks for 12 weeks and in boxes for 4 weeks.

The subsequent growth of plants depended on temperature and period of storage, but did not depend on the kind of vessel in which plants were kept. The height, root system and dry weight of plants which were not stored and plants stored in flasks or boxes at 4°C did not differ significantly (Table 2, Table 3 and Table 4) after 6 weeks of growth in the greenhouse. The period of storage at 4°C did not effect the subsequent growth of plants, but plants kept at 1°C grew worse when they were stored for an extended period of time (Table 2, Table 3 and Table 4). The increase in the branching of plants stored at 4°C for longer period (8 and 12 weeks ) was noticed (Table 5).

Discussion and conclusions

The above results can not be discussed in detail with the results of already published papers. Only Reuther (1983) stated that rooted geranium plants could be stored at low light intensity of 600-1000 lux and 12 hour day-length at 6°C for 3-4 months without a striking depletion of their vigor after potting. The presented results are in accordance with the statements of Maia and Betachini (1977) and Pierik et al. (1979) that rooted gerbera could be stored in vitro at 5°C for at least a few months. However, these authors did not mention anything about the quality of plants after storage. Temperature of 1°C, suitable for apple shoot storage (Lundergan and Janick, 1979), is unfavorable for storage of rooted gerbera.

The storage in boxes for longer periods gave worse effects than storage in flasks. However, the obtained results could satisfy producers of young plants who sometimes cannot afford to transplant plants already taken out of rooting flasks. Such planting material can be kept in boxes or plastic bags at 4°C for 2 weeks without any detrimental effect on its subsequent growth.

Plants stored in rooting flasks at 4°C for 12 weeks were of the same quality as plants which were not stored. It is satisfactory for many laboratories. However, longer storage of rooted in vitro plants could be of great importance for large tissue culture enterprises. Experiments concerning this subject are in progress.

Literature

Earle E. D., Langhans R. W. (1975): Carnation propagation from shoot tips cultured in liquid medium. HortScience 10 (6), 608-610

Hoof P. van (1980): Conservation et multiplication des oeilets in vitro. Revue de l'Agriculture 33 (1), 79-84

Lundergan C., Janick J. (1979): Low temperature storage of in vitro apple shoots. HortScience 14 (4), 514

Maia E., Bettachini B. (1977): Propagation de clones de Gerbera jamesonii par culture in vitro. Travaux sur Gerbera, Jurnee d'etudes du 18 novembre 1977, Frejus, 85-89

Murashige T., Serpa M., Jones J.B. (1974): Clonal multiplication of gerbera through tissue culture. HortScience 9 (3), 175-180

Pierik R.L.M., Steegmans H.H.M., Wouter A.N., Verhaegh J. (1979): Nieuwe ontwikkelingen vegetatieve vermeerdering gerbera in kweekbuizen. Vakblad voor de Bloemisterij 34 (25), 36-37

Reuther G. (1983): Propagation of diseases-free Pelargonium cultivars by tissue culture. Acta Horticulturae 131, 311-319

Roest Jr.S., Bokelmann G.S. (1976): Bewaring van Chrysanthemum morifolium in kweekbuizen. Vakblad voor de Bloemisterij 31 (19), 55