Factors affecting the efficiency of micropropagation from lateral buds and shoot tips of Rubus

Factors affecting micropropagation efficiency of 32 selections of Rubus, including the pre-treatment and initiation culture stages, were investigated. Chilling at 4A degrees C for 6 weeks as a pre-treatment significantly promoted in vitro initiation culture; up to 65% of initiation cultures post chilling were successful. The cytokinin 6-benzyladenine (BA) was the most effective of the three tested for promotion of multiple shoot development in culture, with an average of three to seven shoots or plantlets developed from each single node. Alternating the concentration of BA between 4.44 and 13.31 mu M from sub-culture to sub-culture improved recalcitrant Rubus micropropagation, and reduced the problems associated with long-term culture in the presence of high concentrations of BA. Reduction of the strength of macro- and micro-elements in the basal medium from half to one-third, with addition of 0.49 mu M indole-3-butyric acid and 0.05% activated charcoal, and placing the cultures under reduced light intensity (17 mu mol m(-2) s(-1)), was found to alleviate chlorosis and improve micropropagation with high quality Rubus plantlets. Response to in vitro culture differed greatly and consequently different methods of micropropagation were required by different genotypes. From these selections, three types of micropropagation including micro-cutting, micro-shoots and multi-shoots were observed, and their efficiency was characterized.