Effects of Bio-Stimulants from Freshwater Algae on Growth of Cherry Tomato in Greenhouse

Abstract

This study aimed to investigate the effects of freshwater algal extract as a biostimulant on the growth and yield of cherry tomato (Solanum lycopersicum) cultivated under controlled greenhouse conditions subjected to heat stress (35.0–39.0°C). The experiment was conducted in a closed greenhouse with full sunlight exposure and restricted ventilation to simulate high-temperature stress conditions. A randomized complete block design (RCBD) was employed with four treatments and three replications. The treatments consisted of (1) distilled water as the control (T0), (2) 5 mL algal extract per 1,000 mL water (T1), (3) 10 mL algal extract per 1,000 mL water (T2), and (4) 15 mL algal extract per 1,000 mL water (T3). All treatments received a basal chemical fertilizer (15-15-15) at a rate of 15 g per 20 L of water, applied every three days. Growth and yield parameters were recorded, including plant height, root length, number of flower clusters per plant, number of fruits per cluster, and total  number of fruits per plant. Data were collected from 20 plants per subplot. Leaf chlorophyll content and leaf nitrogen concentration were measured using six leaves per plant. Observations were conducted at 15-day intervals after transplanting (15, 30, 45, and 60 days). Total soluble solids (TSS) was determined at 80 days after transplanting. At harvest, fruit samples were analyzed for amino acid content using an in-house method based on AOAC (1989), and for essential nutrients (N, P, K) using an in-house method based on AOAC (2019). Foliar application of the algal biostimulant was performed four times: at 20 days after transplanting, at the early flowering stage, at the early fruit set stage, and 10 days after the third application. The results demonstrated that treatment T2 significantly (p<0.05) outperformed all other treatments across all measured parameters. The highest mean plant height (103.9±2.7 cm), root length at 45 days after transplanting (26.7±1.1 cm), total fruit number per plant (807.0±3.8 fruits), total soluble solids (9.00±0.00°Brix), and leaf chlorophyll content (39.9±0.4 SPAD) were observed under T2. This was followed by T3 and T1, while the control (T0) showed the lowest performance, with all parameters being approximately 1.5–1.6 times lower. In conclusion, foliar application of freshwater algal extract at 10 mL per 1,000 mL (T2) represents the optimal concentration for enhancing the growth performance and yield of cherry tomato under heat stress conditions.