The Effect of Photon Flux Density and Lighting Period on Growth, Flowering, Powdery Mildew and Water Relations of Miniature Roses

Leiv M Mortensen

doi:10.4236/ajps.2014.513194

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.

Highlights

The photosynthetic active radiation (PAR) at high latitudes in mid-winter is too low for an efficient plant production in greenhouses, and supplementary lighting is established as a standard method for plant growth during the winter months
Increasing the PAR by 25% by increasing the lighting periods (LP) from 16 to 20 h∙day−1 increased the dry weight by about 40%, corresponding to a 1.6% increase in dry weight per 1% increase in PAR
This is a considerable increase when compared with the 0.5% to 1.0% increase in dry weight per 1% increase in PAR evidenced in a literature survey and by interviews with growers done by Marcelis et al [8]

Summary

Introduction

The photosynthetic active radiation (PAR) at high latitudes (about 60 ̊N) in mid-winter is too low (about 1 mol m−2∙day−1) for an efficient plant production in greenhouses, and supplementary lighting is established as a standard method for plant growth during the winter months. Continuous lighting has been found to cause loss of the stomata function, resulting in excessive transpiration and decreased vase life at indoor conditions in some cut rose cultivars [6]. Another effect of LP on cut roses was the development of powdery mildew that more or less disappeared when LP reached 24 h∙day−1 [7]. In the present work the effect of two photon flux densities (PFD) and three lighting periods (LP) on flowering, growth, development of powdery mildew, water relations and keeping quality at indoor conditions were studied. In order to get a better understanding of the light conditions produced by artificial lighting as compared with daylight, information about the natural light throughout the year at different latitudes in Europe is included

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Conclusion