Use of biostimulants to control damages by high temperatures on the growth and flowering of potted cyclamen grown in summer under a Mediterranean greenhouse

Cyclamen is one of the most important flowering pot plants blooming during the autumn and winter and requiring low temperatures, especially during flower differentiation. An average daily temperature (ADT) exceeding 25°C implies risks of heat stress and can heavily affect the quality of the crop, with differences across cultivars. The impact on production is especially evident in plants grown in small pots, which are more susceptible to increased transpiration requirement and root weakening. Excessive temperatures can lead to fewer flower, shorter peduncles so that flowers do not emerge above the leaf level, the production of a supplementary leaf crown and faded flower color. In the Mediterranean areas, temperatures inside greenhouses frequently exceed the optimal range during summer, especially in recent years as a result of climate change. n order to improve the tolerance to high temperature and flower quality of Cyclamen persicum F1 ‘Success Rose Bonbon’, five organic biostimulants [Algavis®, a seawed extract (SWE) from Ascophyllum nodosum; Azobios® a mix of protein hydrolysates (PHs) from animal epithelium; Record®, a mix of plant PHs and SWE; Kappabios®, a protein hydrolizate mix (PHs) from beet vinasse; 66f®,, a plant growth regulator containing naphthalen acetic acid (NAA) and plant extracts] were weekly applied to plant leaves during summer from 6 to 7 leaf stage to the end of cultivation that is the marketable stage. The controls used in the experiment were tap water (Control), a solution with the same N and K concentrations of Kappabios® (Solution 1) or of Azobios® (Solution 2). The ADT exceeded 25°C in more than 40 days during the 2-month growing period. Kappabios® negatively influenced the number of flower (-26.3%) and leaves (-16.8%) compared with the Solution 1, fertilized with the equivalent N and K amounts. Azobios® caused a dry weight loss 
(-10.6%) compared with Solution 2 while Algavis® and 66f® induced no significant effect on plant growth.