Physiological, Yield, and Fruit Quality Responses of Tomato to Irradiated Carrageenan under Drought Stress

This study evaluates the effects of Irradiated Carrageenan Biostimulant (ICB) on fruit yield, quality attributes, biomass allocation, and nutrient assimilation in the commercial tomato hybrid Diamante Max F1 under varying levels of water stress. The experiment, conducted under greenhouse conditions in Los Baños, Laguna, Philippines, included five treatments: T1 – moderate (partial) drought with ICB foliar spray (PD + S), T2 – moderate (partial) drought without ICB (PD + US), T3 – severe drought with ICB (SD + S), T4 – severe drought without ICB (SD + US), and T5 – a fully irrigated, unsprayed control (WW + US). Results revealed significant main and interaction effects of water deficit and ICB on multiple plant indicators. Among the treatments, T2 (PD + S) resulted in the highest total dry biomass. Nutrient uptake, specifically nitrogen (N), phosphorus (P), and potassium (K), showed marked improvement under T1. Drought stress led to an increased root-to-shoot ratio, indicating adaptive allocation toward root development. Yield traits including fruit count, weight, length, and diameter peaked in the PD + S treatment. Furthermore, ICB application enhanced fruit quality parameters such as total soluble solids and titratable acidity particularly under partial drought. These findings suggest that foliar application of ICB under moderate water stress can improve tomato productivity, nutrient uptake, and fruit quality, indicating its potential as a viable biostimulant for drought-resilient tomato cultivation.