ADVENTITIOUS SHOOT REGENERATION FROM INVITRO LEAVES OF SEVERAL PEAR CULTIVARS (PYRUS-COMMUNIS L)

An efficient adventitious shoot regeneration system was developed for pear (Pyrus communis L.), using leaves from in vitro proliferating shoots. Under optimal conditions, bud regeneration frequencies of 'Comice', 'Passe-Crassane', 'Williams' and 'Conference' ranged from 60% to 97%, with the mean number of shoots per regenerating leaf ranging from 3.2 to 6.6. Despite the great variability in responses of the different cultivars, in general an initial dark exposure of at least 20 days was required. Ammonium and total nitrogen proved to play an essential role: Intermediate NH4+ concentrations were suitable for regeneration. The balance between NH4+ and NO3- also influenced regeneration; optimal regeneration occured on media with a 1:3 NH4+/NO3- ratio. TDZ at 1-mu-M was less efficient than higher concentrations, whatever the NAA level. Finally, length and growth regulator composition of the two phases (induction and expression) influenced the regeneration rate of 'Conference'.