TITLE:
The Effect of Photon Flux Density and Lighting Period on Growth, Flowering, Powdery Mildew and Water Relations of Miniature Roses
AUTHORS:
Leiv M. Mortensen
KEYWORDS:
Flowering, Growth, Keeping Life, Leaf Water Loss, Lighting Period, Miniature Rose, Photon Flux Density (PFD), Photosynthetic Active Radiation (PAR), Powdery Mildew
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.5 No.13,
June
5,
2014
ABSTRACT: Miniature roses (Rosa sp.)
were grown at 100 and 150 μmol m-2·s-1 photon flux
densities (PFD) with 16, 20 and 24 h·day-1 lighting periods (LP) in
a greenhouse compartment in midwinter at latitude 59° north. The study included 10 different
treatments and six rose cultivars, altogether 900 plants. The 16 and 20 h LP
were applied with or without a dark period of 8 and 4 h·day-1, respectively,
by timing the LP in relation to daylight that lasted for 7 - 8 h. Number of
days until flowering decreased with an increase in PFD and in LP up to 24 day-1 and was unaffected by the timing of the 16 and 20 h·day-1 LP. Number
of flowers and plant dry weight increased 20% to 30% by increasing the PFD.
Plant dry weight increased by increasing the LP from 16 to 20 h·day-1 (about 25%), but no effect was found with a further increase to 24 h·day-1.
Mean growth rate until flowering increased 30% to 40% by increasing the PFD or
by increasing the LP from 16 to 20 h day-1, while little effect was
found by a further increase to 24 h·day-1. Increasing the photosynthetic
active radiation (PAR) by increasing the LP from 16 to 20 h·day-1 increased the growth rate more than increasing the PFD did. Three of the
cultivars were tested for water loss after the detachment of some leaves.
Leaves that had developed without a dark period showed a considerably higher
water loss than the treatments that included a dark period of 4 or 8 h·day-1.
The keeping quality at indoor conditions, however, was unaffected by the
treatment due to sufficient watering. Powdery mildew developed significantly
more on plants grown with a dark period of 8 h as compared with the other
treatments. It was concluded that 20 h·day-1 LP including a dark
period of 4 h·day-1 and a PFD of at least 150 μmol·m-2·s-1 should be applied to miniature roses during the winter months in order to effectively
produce miniature pot roses with a high quality.