Effects of Depolymerized Gellan with Different Molecular Weights on the Growth of Four Bedding Plant Species

New solutions allowing for the shortening of the growing cycle and improvements in plant quality are constantly sought in order to improve the efficiency of bedding plant production under covers. Biodegradable polysaccharides and their derivatives have become increasingly popular in horticulture as plant growth promoters. A greenhouse pot experiment was conducted to evaluate the effects of depolymerized gellan of different molecular weights (M-W 56 kDa and 77 kDa) on the growth and physiological parameters of ornamental bedding plants Rudbeckia hirta L., Salvia splendens Sellow ex J.A. Schultes, Scabiosa atropurpurea L., and Tithonia rotundifolia (Mill.) S.F. Blake. The results showed that the application of depolymerized gellan accelerated flowering and stimulated the growth of all assessed species, regardless of M-W. The plants treated with depolymerized gellan grew higher and had greater fresh weight of their above-ground parts, higher leaf relative chlorophyll content (SPAD; soil and plant analysis development), and higher stomatal conductance (g(s)). The use of 56 kDa gellan fraction resulted in the formation of inflorescences with the greatest fresh weight in S. atropurpurea. Leaves of R. hirta treated with this fraction showed the highest values of SPAD and g(s). This study demonstrated that gellan derivatives of low M-W may be used for the production of innovative plant biostimulants.