Effect of Spectral Composition in LED Supplementary Lighting on the Growth and Development of Micro Plants Belonging to Genus Rubus L. at the Adaptation Stage

The effect of the spectral composition of LED supplementary lighting exerted on the growth and development of micro plants belonging to the genus Rubus L. at the ex vitro adaptation stage in a heated greenhouse are assessed. The material for the studies is represented by rooted microplants of the Columbia Giant blackberry variety and the loganberry and tayberry blackberry–raspberry hybrids obtained by clonal micropropagation and planted in cassettes with a peat substrate. In the control, they are exposed only to natural sunlight. In the experimental variants, to compensate for the shortened light period typical of March, in addition to natural light, supplementary lighting is used with various types of LED lamps having different spectral composition: full-spectrum (with maxima at a wavelength of 453 and 598 nm), blue-red spectrum (at 460 and 630 nm), and red spectrum (maximum at a wavelength of 630 nm). The duration of the supplementary lighting amounts to 8 h in two cycles of 4 h per day at an illumination intensity of 120 μmol/(m² s). Supplementary lighting was carried out throughout the entire month (for 31 days), after which a set of morphophysiological parameters were analyzed in ten plants in triplicates. High correlations are observed between the values of the dry weight of the whole plant and its roots (r = 0.84–0.99; p < 0.04), between the dry weight of roots and their fraction in the plant weight (r = 0.90–0.98; p < 0.04), between the leaf area and the dry weight of roots (r = 0.77–0.84; p < 0.05), and between the concentration of the sum of chlorophylls and carotenoids (r = 0.80–0.99; p < 0.04). Upon full-spectrum supplementary lighting, all the genotypes have shown an increase in the plant leaf area when compared to the reference by 1.2–1.4 times and that in the dry weight of roots by 1.2–2.0 times. The maximum concentration of photosynthetic pigments in the experiment is revealed for the variant with a red-blue spectrum of supplementary lighting, in which it is 1.3–1.9 times higher than in the case of the reference.