Influence of cobalt concentration on the growth and development of Dendrobium kingianum Bidwill orchid in an in vitro culture

The study investigated the influence of increased cobalt content in urashige and skoog (1962) solid medium on the growth and development of Dendrobium kingianum Bidwill orchid plants. Explants of shoots were used for micropropagation of the orchid plants on MS regeneration medium supplemented with 0.5 mg dm -3 NAA and 1.0 mg dm -3 kinetin. Cobalt (as CoCl 2 · 6H 2 O) was added to all treatments in concentrations of 0.025 (control), 0.625, 1.25 and 2.5 mg dm -3 . The results obtained after eight months showed that treatments with the cobalt chloride in concentrations 0.25-1.25 mg dm -3 did not influence the number of shoots and roots, and the length of shoots of the orchids. The treatment with the cobalt chloride in concentration 0.625 mg dm -3 positively influenced on the length of roots and increment of the fresh weight of plantlets. However, in media with the highest cobalt concentration (2.5 mg dm -3 CoCl 2 · 6H 2 O), a negative influence of the metal on the number of shoots of the orchids was noted. Spectrophotometric analysis (ASA) showed that cobalt accumulation increased in both the shoots and the roots with the increase in the external Co level, whereas iron accumulation in these organs decreased. Cobalt and iron accumulation in the roots was 3-4 times higher than in the shoots.

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