ABSTRACT Plant biostimulants are commercial products based on different chemical substances used to enhance plant growth and productivity. The effects of biostimulants, Megafol and Viva, with different dominant compositions (amino acids and humic acids) on two tomato cultivars (cv. Gravitet F1 and cv. Minaret F1) exposed to conventional and low-input macronutrient nutrition were investigated. Application of both biostimulants positively affected yield at conventional nutrition. In low-input nutrition variant, biostimulant application prevented yield loss only in cv. Minaret F1. Inter-cultivar differences were noticed in fruit characteristics (total phenol content, total flavonoids content and total antioxidative capacity) where application of biostimulants leads to opposite results in the examined cultivars. We considered the possibility of biostimulant usage as an effective nutritional addition for overcoming the problem of excessive fertilisation.

Two commercial tomato cultivars were used to determine whether grafting could prevent decrease of Ca2+ concentration under salt stress conditions. The cultivars Buran F1 and Berberana F1 were grafted onto rootstock "Maxifort" and grown under three levels of the elevated soil salinity (S1 EC 3.80 dS m-1, S2 6.95 dS m-1 and S3 9.12 dS m-1). Ca2+ concentration of non-grafted plants of both examined hybrids was lower at all salinity levels in comparison to the control. In the fruits of grafted plants salt stress significantly decreased Ca2+ concentration only at the third salinity level (EC 9.12 dS m-1). The possibility of grafting tomato plants to improve influx of Ca2+ under salt stress conditions is discussed.

Salinity is one of the most important ecological problems that affect irrigated agriculture in the world. Increased soil salinity inhibits plant growth through osmotic and ionic stress, but can also decrease availability of certain micronutrients. Copper is an essential metal for normal plant growth and development that participates in numerous biochemical and physiological processes and it is an essential cofactor for many metalloproteins. Copper concentration in two commercial tomato cultivars (grafted and non-grafted) was investigated under different levels of elevated soil salinity. Soil with EC 9.1 dS m-1 led to the highest copper deficiency, approximately by 37% in the non-grafted and 25% in the grafted tomato plants. The effect of a grafting technique is considered as an environmentally friendly tool for overcoming soil salinity problem.

An experiment was carried out to determine the effect of foliar application of seaweed extract (0.2 %) on the growth, yield and quality of cherry tomato under stress and non-stress conditions. The greenhouse experiment was set up in a randomized block design with four treatments in three replications. Treatments were as follows: V1 - seedlings treated by seaweed extract and subjected to drought; V2 - seedlings treated by seaweed extract and regularly watered; V3 - non-treated seedlings subjected to drought; V4 - non-treated seedlings regularly watered. Cherry tomato seedlings treated by seaweed extract had a lower content of proline and higher leaf water potential compared to non-treated seedlings under stress conditions, indicating that application of this fertilizer contributes to better adaptation of cherry tomato seedlings to stress. Treatment with seaweed extract also positively influenced the yield and quality of cherry tomato (total soluble solids, vitamin C, lycopene) under both standard and drought stress conditions as compared to untreated plants in same conditions. Positive effects of seaweed extract on growth and quality of cherry tomato are result of its specific composition, as well as ability of cherry tomato plants to utilize bioactive substances in seaweed extracts for its growth and development.

Murtic S., Oljaca R., Koleska I., Karic L., Todorovic V. (2018): Response of cherry tomato seedlings to liquid fertiliser application under water stress. Hort. Sci. (Prague), 45: 22–28. The aim of this study was to examine the impact of different liquid fertilisers on selected physiological parameters in order to evaluate the drought tolerance of cherry tomato seedlings. The following physiological parameters were investigated: total phenolic and flavonoid content, total antioxidant capacity and proline content of leaf extracts. Total phenolic and flavonoid content were determined using the Folin-Ciocalteu and aluminium chloride colorimetric methods, respectively. The ferric-reducing/antioxidant power (FRAP assay) was used to measure the total antioxidant capacity, while proline content was evaluated according to the method of Bates. The contents of proline, total phenolics and flavonoids were significantly higher in the leaves of cherry tomato seedlings exposed to water stress, which suggests that the higher synthesis of these substances by plants represents an important defence mechanism of drought tolerance. The results also indicate that the application of all the used fertilisers in accordance with the manufacturer’s instructions can significantly increase the content of phenol compounds and total antioxidant capacity of plants under normal growth conditions, thus improving survival under subsequent stress.