Epsilon Open Archive

Abstract

Light-emitting diodes (LEDs) have emerged as a promising artificial lighting source in greenhouse production of horticultural crops, as they reduce energy consumption. However, changes in lighting technology are known to affect abiotic and biotic interactions in the phyllosphere, e.g. LEDs can change the microclimate within the greenhouse and around the crop, and thus the microbial community structure. Information is lacking on interactions between light spectra and microbiota associated with the canopy, the function of non-phototrophic bacteria associated with the phyllosphere and successful administration of microbial biocontrol agents.

This thesis investigated the impact of different light spectra on plant physiological parameters, microbial community structure, utilisation pattern of energy sources and biosurfactant formation by phyllosphere microbiota in greenhouse-grown ornamentals. A standard protocol for extraction of phyllosphere microbiota, impact of plant species and leaf position, and antagonistic activity of resident phyllosphere microbiota against Botrytis cinerea was also studied. Use of culture-dependent methods revealed higher numbers of culturable fungi on basal than on apical leaves, but the numbers did not vary with different light treatments. Metagenomics showed that the fungal microbiome was more diverse on apical leaves. Interactions were found between leaf temperature and many dominant bacterial genera. In vitro tests revealed that inhibitory effects of some strains identified by 16S rRNA varied with respect to different media. Phenotypic microarray analysis revealed that light treatments had considerable effects on substrate utilisation by two Pseudomonas strains and moderate effects on Streptomyces griseoviridis, with blue LEDs having most the pronounced impact. Biosurfactant formation by Pseudomonas strains was supported by most substrates when incubated in darkness, but blue LED altered the surface activity more profoundly.