Six groups of plants (Cl-C6) were used in the present study. Plant material and climate
conditions were different for each group:
( 1) for the C l-C3 groups, leaf cuttings of Begonia X hiemalis cv. “Heidi” were grown in a glasshouse at INRA Montfavet (southern France) from February to May 1992 (Cl ), Five weeks after planting, 100 plants from the greenhouse were placed in a growth chamber with constant air temperature (20 f 2°C) and relative air humidity (70 f 10%) and divided in two groups, C2 and C3, differing in the level of incident PPFD: 200 pm01 photon m-’ s- ’ and 400 pmol photon m -’ s-’ for C2 and C3, respectively.
(2) For the C4 and C5 groups, shoot cuttings of Begonia X hiemulis cv. “Line” were grown in the same glasshouse during two periods: October 1992-February 1993 (i.e. a winter culture; C4) and March-June 1993 (i.e. a spring culture; C5).
(3) For the C6 group, shoot cuttings of Rosalie group cultivars were grown during winter 1992-1993, in a production glasshouse, at CNIH (Comite National Interprofessionel del’Horticulture), Angers (western France).