The olive tree undergoes significant stress with high temperatures and irradiance levels occur during the growing season. Various products are used to ameliorate the negative effects of abiotic stress in plants, aiming at different physiological, biochemical and morfological functions such as the use of plant products that attracte considerable interest from the scientific community and commercial enterprises. Many products of biological origin have significant potential for improving physiological processes in plants and stimulating germination, growth and stress tolerance.

The aim of the research was to examine the effects of a plant-derived anti-transpirant (Vapor Gard®, VG) on the growth of 2 years old olive trees subjected to high temperature in nursery. Vapor Gard® is a water emulsifiable organic concentrate of di-1-p-menthene (C₂₀H₃₄), a terpenic polymer also known as pinolene. The study was carried out in greenhouse on trees of native cultivar of Campania (cv Salella) grown in pot, during the growing season from may to september 2020. The experimental design included anti-transpirant product (VG) applied 5 times at 20 days intervals compared with a Control, each thesis, consisting of 10 trees. On trees was evaluated: stomatal conductance, chlorophyll a fluorescence, SPAD index, RWC, growth of shoots, total leaf area per plant, trunk croos-sectional area and dry matter partitioning.

The results obtained show that applications of di-1-p-menthene are able to induce a significant improve of the shoots growth (+25.1 %) and trunk croos-sectional area (27.07 vs 39.18 mm²). At same time a significant reduce of the stomatal conductance and an increase of leaf RWC values were recorded. The treatment with the anti-transpirant also favored the increase of SPAD values of leaves (+4.4 %). At the end of the experiment the treated trees had greater total dry matter than the control (+10.8 %).