Slow growth in 'Pisana' apricot and in 'Cerina' apple, two Italian cultivars

The storage of micropropagated plants in slow growth has the aim to reduce the frequency of periodic sub-culturing. The most commonly applied conditions include low temperature, darkness and addition of sugars to the medium. Encapsulation technology is also used. The mid-term storability, at 4°C, in darkness, of ‘Pisana’ apricot and ‘Cerina’ apple was evaluated. Shoots of ‘Pisana’ were multiplied in presence of equimolar amount of sucrose or sorbitol and benzyladenine or meta-Topolin and nodal segments from shoots were maintained, for 6 months, ‘naked’ or encapsulated in alginate, on media with 3, 4.5 or 6% sucrose. Each 21 days, nodal segments from each treatment were transferred in standard growth conditions and regrowth was recorded after 21 days, as number of nodal segments developing shoots. After only 21 days the re-growth of explants multiplied on sucrose/benzyladenine was significantly lower than control, while for those multiplied on sorbitol/meta-topolin the regrowth reduction was significant only for encapsulation treatments and for the highest sucrose concentrations. However, the regrowth ability decreased linearly with the time for all treatments and the encapsulation had a detrimental effect on the regrowth. In ‘Cerina’, two sucrose concentrations (3.0 or 4.5%), salicylic acid (0.5 mM) or L-glutamine (5 mM) were applied. Shoots were stored in darkness at 4°C for 1, 3 and 6 months. At the end of each period the extension of necrosis in the shoots was evaluated and then shoots were transferred to standard growth conditions. After 21 days, multiplication rate and chlorophyll content were determined. The most effective treatment in limiting necrotic areas and the reduction of chlorophyll content was the supply of sucrose 4.5% in the medium. Salicylic acid significantly extended necrosis in explants, with a progressive increasing with the cold storage time, did not avoid reduction of chlorophyll content and induced a significantly an increase of carotenoids content.