CULTURE PHENOTYPE AFFECTS ON REGENERATION CAPACITY IN THE MONOCOT HAWORTHIA-COMPTONIANA

Haworthia comptoniana specimens were cultured to determine how benzyla denine (BA) level and in vitro selection for shoot and callus producti on affected regeneration capacity and plant phenotype. Leaf explants w ere cultured on Murashige and Skoog medium containing 0 to 10 mg . lit er-1 of BA. The highest number of shoots was obtained with 0.5 mg . li ter-1 of BA. H. comptoniana stock cultures (hc) maintained with 0.5 mg . liter-1 of BA produced clumps of small shoots interspersed with fri able, white, tan, and green callus. A clump of very large shoots was i solated and designated cell line Rhc; it differed from the original hc culture in shoot size, the lack of callus growth, and higher water co ntent. A line of green callus (designated Gc), a line of white callus (Wc), and a line of soft tan callus (Tc) were also isolated from hc. O ptimal BA levels for shoot regeneration from lines Gc and Wc were 2 an d 5 mg . liter-1, respectively. No normal shoots could be regenerated from Tc. The phenotypes of these cell lines remained stable for 24 sub culture generations. The hc line that initially required BA for growth became hormone autotrophic whereas the other lines did not. Culturing using Gelrite and sealing vessels with parafilm promoted vitrificatio n of the hc line. Culturing using GIBCO agar and unsealed vessels redu ced vitrification. The ex-vitro greenhouse survival rates for hc and R hc plantlets were 10 and 80%, respectively. The large size of the Rhc shoots apparently resulted in significantly higher survival rates unde r greenhouse conditions, but did not result in any phenotypic whole pl ant changes.