CONSEQUENCES OF INVITRO AND EXVITRO ROOT INITIATION FOR MINIATURE ROSE PRODUCTION

Microshoots of Rosa chinensis var. minima (cvs Debut, Ginny, Red Ace and Tipper) were rooted using standardized in vitro and ex vitro root initiation techniques, then comparatively examined with regard to anatomical and morphological root character and effect of root initiation treatment on later plant development. After 18 days of in vitro or ex vitro rooting treatment, comparable rooting ranging from 95-100% was obtained for three of the four cultivars. Ex vitro rooting promoted longer roots and a tendency for both higher root number and area. Ex vitro roots were flexible, white, and produced branch roots while in vitro roots were brittle, darkened and did not branch. Cross sectional data revealed that ex vitro roots were thinner, possessed root hairs, and tended to have greater vascular area to root area with advanced development of the vascular tissue than in vitro-produced roots. Ex vitro-rooted plants of all cultivars except 'Ginny' had greater root growth (area and dry mass) and shoot growth (height, area, and dry mass) 88 d after transfer to rooting than their in-vitro rooted counterparts. For all cultivars, improvement in flower production was seen in a greater number of flowers and/or a lower number of days to flowering for ex vitro-rooted plants.