| Summary: | Thesis (MA)--Stellenbosch University, 2018. ENGLISH ABSTRACT: Light quantity and quality plays a fundamental role in seed germination, plant growth and development. Plants grown in high radiation regions can experience light stress, resulting in photoinhibition when the photosynthetic capacity of the light harvesting complexes in the photosystems are over-exposed. Shade nets are a cost-effective way to reduce high light quantities and to create a more desirable growing environment. Black shade nets are used widely for vegetable seedling and mature crop production in South Africa, due to its cost effectiveness and availability. Although, recent studies have indicated that coloured shade nets can increase plant responses and physiological processes like seed germination, plant architecture, circadian rhythms as well as plant growth and development. Chlorophyll fluorescence is a non-destructive method used to determine the amount and type of plant stress when a plant is exposed to sub-optimal growing conditions. Unfortunately, no literature could be found to indicate specific chlorophyll fluorescence parameter values, for lettuce and cabbage seedlings and mature crops, grown under different coloured shade nets in high solar radiation environments, and low radiation LEDs. The objective of this study was two-fold. Firstly, to determine the chlorophyll fluorescence parameters for lettuce and cabbage seedlings and mature plants produced under different coloured shade nets with high solar radiation, and the leaf macro- and micro-element composition of lettuce and cabbage seedlings and mature plants, and physical analyses of mature cabbage plants. Secondly, to determine chlorophyll fluorescence parameters, and leaf macro- and micro-element composition of lettuce seedlings, under different colour combination low radiation LEDs. The research was conducted by means of three replicates of five different coloured shade nets – with the black net as the control. ‘Grand Slam’ and ‘Islandia’ lettuce, and ‘Conquistador’ and ...
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