Development rate of young greenhouse rose plants ( Rosa hybrida) rooted from cuttings in relation to temperature and irradiance

Abstract

The development rate of 13 genotypes of greenhouse roses was observed for young plants rooted from cuttings and grown in a phytotron or greenhouse. The development was divided into three stages from pinching to anthesis: Stage 1, shoot 0 cm (pinching) to 1 cm long (bud break) (0 → 1); Stage 2, shoot 1 cm long to visible floral bud (B) (1 → B); Stage 3, visible floral bud to anthesis ( B → F). In the phytotron, with photosynthetically active radiation (PAR) from 0.65 to 2.60 MJ m −2 day −1, each phase of Rosa hybrida cultivar ‘Sonia’ had different responses to irradiance and mean air temperature ( T). The duration ( d) of Stage 1 was primarily a function of T, that of Stage 2 was a power function of PAR and a parabolic or hyperbolic function of T: d 1 → B = k × PAR x × f( T). The duration of Stage 3 was much less sensitive to PAR, and was a parabolic or hyperbolic function of T. In the greenhouse, with miniplants grown at different seasons, these equations for the effects of T and PAR were applied and validated with at least the ten varieties which rooted normally during the cutting process, and which flowered normally even in winter. Owing to a strong interaction of PAR and T in the greenhouse, the varietal PAR effects should be determined principally in a phytotron, then the T effect may be determined in a series of greenhouse experiments.