Rooting response of Prunus domestica L. microshoots in the presence of phytoactive medium supplements

The study aimed at evaluating the response of common plum (Prunus domestica L.) microshoots during in vitro rooting in the presence of two phytoactive medium supplements, i.e. a dialyzate of pineapple pulp and a conditioned medium containing green algae Desmodesmus subspicatus exudates. Rooting efficiency was evaluated after 4 weeks of culture. During the root induction phase the content of phenolic compounds in shoot bases was determined and anatomical studies were conducted. Medium supplements were analyzed for the content of carbohydrates and phenolic acids. Both supplements were efficient in rooting induction of shoots of a difficult-to-root cultivar 'WA (TM) gierka Zwyka'. Medium supplementation allowed a significant reduction in the exogenous auxin content required for rooting. The highest rooting efficiencies on supplemented media were 28.9 and 27.8 %, in comparison with 33.3 % obtained in the control medium with doubled concentration of exogenous auxins. In the easy-to-root plum cultivar 'WA (TM) gierka DA...browicka' the rooting rate was slightly reduced in the presence of pineapple dialyzate, while in the presence of algal conditioned medium the rooting rate decreased substantially compared with the non-supplemented medium. Approximately 30 % of 'WA (TM) gierka DA...browicka' shoots rooted on supplemented auxin-free media. The content of phenolic compounds accumulated in shoot bases during the root induction stage reflected the differences in rooting ability between both plum cultivars, indicating potential stressful conditions of the culture generated by the presence of phytoactive natural supplements. Anatomical study allowed to recognize the mode of dedifferentiation leading to adventitious rhizogenesis in the common plum. The results are discussed in relation to the composition of medium supplements and their potential root-promoting activity.