The Effect of Supplementary LED Lighting on the Morphological and Physiological Traits of Miniature Rosa × Hybrida 'Aga' and the Development of Powdery Mildew (Podosphaera pannosa) under Greenhouse Conditions.

Bożena Matysiak

doi:10.3390/plants10020417

Abstract

We investigated the growth traits, flower bud formation, photosynthetic performance, and powdery mildew development in miniature Rosa × hybrida ‘Aga’ plants grown in the greenhouse under different light-emitting diode (LED) light spectra. Fluorescence-based sensors that detect the maximum photochemical efficiency of photosystem II (PS II) as well as chlorophyll and flavonol indices were used in this study. Five different LED light treatments as a supplement to natural sunlight with red (R), blue (B), white (W), RBW+FR (far-red) (high R:FR), and RBW+FR (low R:FR) were used. Control plants were illuminated only by natural sunlight. Plants were grown under different spectra of LED lighting and the same photosynthetic photon flux density (PPFD) (200 µmol m−2 s−1) at a photoperiod of 18 h. Plants grown under both RBW+FR lights were the highest, and had the greatest total shoot length, irrespective of R:FR. These plants also showed the highest maximum quantum yield of PS II (average 0.805) among the light treatments. Red monochromatic light and RBW+FR at high R:FR stimulated flower bud formation. Moreover, plants grown under red LEDs were more resistant to Podosphaera pannosa than those grown under other light treatments. The increased flavonol index in plants exposed to monochromatic blue light, compared to the W and control plants, did not inhibit powdery mildew development.

Highlights

Roses (Rosa sp.) are the most important ornamental plants worldwide
The modern technology of light-emitting diode (LED) lighting allows producing high-quality potted roses grown in greenhouses under unfavourable light conditions, and suppressing powdery mildew development (Podosphaera pannosa)
An optimal effect related to maximizing plant quality and minimizing powdery mildew infestation can be obtained with a relatively high share of red light (49–67%) in combination with blue (13–16%) and green–yellow fractions of visible light (10–15%) at a photosynthetic photon flux density (PPFD) of 200 μmol m−2 s−1 for 18 h, and at an R:FR ratio from 2.1 to 11.3

Summary

Introduction

Roses (Rosa sp.) are the most important ornamental plants worldwide. The EU is the most important production area for ornamental plants in the world, and holds the first place in cut flower and potted plants with 31.0% of the global value [1]. EU production of flowers and ornamental plants in 2019 was worth 22.099 million Euros. Roses are the number one cut flower on the European market, and potted roses are among the top five best-selling potted plants. In northern Europe, the relatively low natural light intensity and short days during winter result in fewer axillary shoots, lower fresh weight and diameter of flower stems and buds, lower leaf area, lower number of petals per flower, and poorer pigmentation [2,3]. Greenhouse-grown roses require supplementary lighting during winter

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