Influence of sucrose concentration on in vitro rooting, growth, endogenous sugars and ex vitro survival of juvenile avocado

The use of varying sucrose concentration in the culture medium as an in vitro preconditioning treatment to check the possible influence on ex vitro acclimatization of micropropagated avocado (Persea americana Mill) plantlets was studied. Effects of sucrose on in vitro rooting, shoot elongation, leaf development, levels of endogenous sugars in roots and leaves, and ex vitro survival rate were evaluated during the in vitro rooting period and subsequent acclimatization stage. Pretreatment with high sucrose diminished in vitro root induction and did not improve survival rate of juvenile avocado. Shoot elongation was stimulated and leaf development remained unchanged during the in vitro rooting phase and a reverse trend was noticed during acclimatization. The high sucrose treatments had no influence on sucrose contents in leaves or roots during the in vitro rooting phase but decreased sucrose in roots during ex vitro acclimatization. An elevated level of starch and a decline in sucrose in leaves of plantlets grown ex vitro indicate a preferential utilization of sucrose for ex vitro establishment by avocado plantlets. Overall results suggest that under standard environmental conditions, a moderate sucrose concentration in the culture medium is adequate to acclimatize micropropagated avocado.