In vitro bulb induction in Eucomis zambesiaca Baker.

Abstract

Eucomis L’ Hér. is a genus of 10 species that fall within the Hyacinthaceae family. Eucomis zambesiaca Baker is a summer-blooming bulbous geophyte occurring from northern South Africa to Malawi. Eucomis species are used in southern African traditional medicine for the treatment of various ailments, in particular, pain and inflammation. As a result, the bulbs are heavily harvested for trade in South Africa’s traditional ‘muthi’ markets. Over-collection of Eucomis species has seriously depleted natural populations and now Eucomis plants are among the 15 scarcest medicinal species to be traded. Micropropagation is a useful technique for rapid clonal multiplication of plant material which could potentially yield useful secondary metabolites as well as alleviate the pressure on the wild plant populations. The in vitro induction of storage organs is especially beneficial as it can limit the loss of plants during acclimatization as bulblets are hardier than shoots or plantlets. The aim of this research was to determine optimal growth conditions for bulblet induction of Eucomis zambesiaca. The effect of environmental and physiological parameters on the initiation and growth of bulblets was investigated. These included the effect of temperature, photoperiod, various carbohydrates at different concentrations and combinations as well as various plant growth regulators. Maximum number of bulblets per explant was obtained at 20 °C, with an average of three bulbs p er leaf explant. The average bulblet mass was 57 mg, which was significantly higher than bulblets formed at other tested temperatures. An 8 h light regime was the optimum photoperiod. The highest mean number of bulblets (1.4 per leaf explant) developed under the 8 h photoperiod and the bulblets that formed were large in size. They had a mean bulb diameter of 3.4 mm and a mean bulb weight of 42 mg. Different carbohydrates such as fructose, sucrose and glucose were tested at concentrations of; 1, 3, 6, 9 and 12%. Fructose at a concentration of 3% was found to produce the best results. An average of 1.2 bulbs formed per explant. The mean bulb diameter was 3.4 mm and mean bulb weight was 56.6 mg. Plant growth regulators (GA3, IAA, IBA, NAA, BA, zeatin, iP and others) were tested at concentrations of 1, 2 and 5 mg/L. 1 mg/L IBA was found to be the optimum hormone treatment for bulblet induction. Bulblets were large, had good leaves and well established roots. Medium supplemented with 1 mg/L IBA produced bulblets that had an average bulb diameter of 4.36 mm and a mean bulblet weight of 79.1 mg. Bulblets grown in vitro were transferred to vermiculite and placed in a misthouse to acclimatize. After 2 months the plantlets were transferred to pots containing a sand:soil mixture of 1:1 and placed in a greenhouse. There was a 80 to 90% survival rate.