In vitro growth response of Prunus Cerasifera shoots as influenced by different light-dark cycles and sucrose concentrations.

Trials were carried out to test if the higher growth response shown by shoot clusters of Mr. S. 2/5, a clonal selection of Prunus cerasifera, submitted to short and frequent light-dark regimes could be related to the amount of sucrose added to growth medium. The reduction of sucrose from 30 gl-1 (control) to 22.5 gl-1, 15 gl-1 and 7.5 gl-1 caused a progressive and remarkable inhibition of shoot tip growth. With 15 gl-1 the value of some growth parameters was reduced by more than half. Under 16-h daylength, the best sucrose concentration was 30 gl-1, while with 4-h light-2-h dark no statistical differences appeared between 30 gl-1 and 22.5 gl-1 sucrose. Compared to 16-h light-8-h dark, the 4-h light-2-h dark cycle at the three highest sucrose concentrations gave rise to higher values of fresh and dry weight as well as increasing the number of axillary shoots produced. The increment in growth response induced by the shorter light-dark regime decreased with diminishing growth capacity in the cultures when sucrose concentration was lowered, but it was still appreciable even with 7.5 gl-1. Since the 4-h light-2-h dark cycle induced a favourable effect in culture growth with all sucrose concentrations, we conclude that the greater growth response observed with this light regime was not triggered by carbohydrate availability but by some other unknown factors.