Nutrient status, growth and proline concentration of French marigold (Tagetes patula L.) as affected by biostimulant treatment
French marigold (Tagetes patula L.) is becoming very popular decorative flowering species in city parks due to its beautiful coloured flowers and resistance on drought stress. Transplants of French marigold are usually being produced in greenhouses allowing early planting outdoors. Such early transplanting due to temperature stress negatively affects nutrient uptake and transport, plant growth, and can also cause plant death. To avoid such scenario, different growth stimulants can be used to treat plants. The aim of this investigation was to determine the effect of organic biostimulant application on French marigold growth and development after transplanting. Investigation was carried out in heated and non-heated greenhouses located in Banja Luka, Bosnia and Herzegovina. Trial was set out in a split-plot design containing treated and untreated plants during three years of investigation. Treated plants were watered with biostimulant Radifarm® in concentration of 0.25% whilst untreated plants were watered only with water. Duration of trial was two months, where treatments with biostimulants were performed every seven days each year of investigation. At the end of the trial roots and above-ground part weight, number of leaves, flowers and buds and plant height were recorded. Additionally, concentrations of N, P, K, Ca and Mg in roots and above-ground part as well as proline concentration in leaves were measured. Obtained results showed positive influence of biostimulant treatment on plant growth and development after transplanting. French marigold roots and above-ground part weight as well as plant height were significantly higher in treated compared to non-treated plants. Also, significantly higher number of leaves, flowers and buds was recorded in treated plants comparing to control plants. Furthermore, higher concentrations of N, P and K, especially in plant above-ground part, were recorded in treated than in non-treated plants. Overall, biostimulant application facilitated the plant to overcome stress caused by transplanting and low temperatures. This ensured continuous plant growth and development which is especially important in fast-growing species such as French marigold.