Yield, quality, and antioxidants of greenhouse grown ‘miniplum’ tomato as affected by biostimulant treatment duration in southern Italy

A study was conducted in Naples to assess the effects of biostimulant application on yield and quality of miniplum tomato in saline soils. The experiment was based on the comparison between four levels of soil electrical conductivity (EC of 1.5, 3.0, 4.5, or 6.0 mS cm^‑1) in factorial combination with four durations of the biostimulant Activeg treatment (3, 6, or 9 applications, plus an untreated control), using a split-plot design with three replications. The flowering and fruit set started on July 12 for biostimulant-treated plants and two days later in the untreated control; the soil EC of 6 mS cm^‑1 resulted in two days earlier flowering compared to the lowest EC (1.5 mS cm^‑1). The interaction between biostimulant treatment and electrical conductivity had a significant effect on fruit yield. The 6 or 9 times biostimulant treatments led to the highest yield at the 3.0 mS cm^‑1 EC, and the lowest at 6.0 mS cm^‑1 EC. Fruit harvest started three days earlier under the 6 mS cm^‑1 EC treatment compared to 1.5 mS cm^‑1 EC. Both the experimental treatments applied had significant effects on the quality and antioxidant variables examined, such as dry residue and soluble solids, lycopene, polyphenols, ascorbic acid, and antioxidant activity in tomato fruits. The biostimulant treatment had a significant effect on the fruit colourimetric indices A* and B*. In this research, the best yield results of ‘Proxy F₁’ miniplum tomato were obtained under the biostimulant treatment repeated 9 times at 3 mS cm^‑1 soil electrical conductivity.