EFFECT OF CYTOKININ AND KIND OF EXPLANT UPON FRIAR'S CROWN IN VITRO SHOOT FORMATION

Friar crown or coroa-de-frade (Melocactus zehntneri) is a globular cactaceae with high ornamental value. They mainly occur at Brazilian Northeast and Bahia State has the highest diversity. They are slow-growth species, whose reproductive stage begins around 10 years old. Wild populations do not present lateral shoots. Caatinga degradation and illegal commercialisation of them has threatened some of these species. Thus, tissue culture techniques are an alternative way as to conserve as to multiply plants with agronomic interest. In this work, in vitro 19-months-old friar crown seedlings about 3 cm high were used. The plants were transversally cut in three kinds of explants: apical, median and basal. A completely randomized design in factorial scheme 5×3 was used, in which factor A was BAP concentration (0, 1, 2, 4, 8 mg L^-1) and factor B was the different kinds of explants, in a total of 15 treatments, with 5 repetitions of 5 flasks with one explant each. Culture medium JADS was used with 30 g L^-1 of sucrose and 2 g L^-1 of Gelrite^®. The flasks had an internal volume of 250 ml and were filled with 40 ml of culture medium. The experiment was conducted for 60 days in a growth chamber at 27±2°C, photoperiod of 12 hours and photo-synthetically active radiation of 30 μmol m^-2 s^-1. The statistical analysis showed that both factors were significant. The greater shoot number was at 8 mg L^-1 of BAP in accordance to a sigmoidal curve and the explants have relationship to the natural cytokinin distribution, with the greater number of shoot formation at basal explants.