Optimizing Hydroponic Management Practices for Organically Grown Greenhouse Tomato under Abiotic Stress Conditions

Hot and humid conditions create challenges for tomato production under a controlled environment. Low tomato productivity is related to the lack of stress tolerance of existing cultivars and their ability to maximize fruit set and yield. The aim of this study was to evaluate the effectiveness of three management strategies, cultivar selection, grafting, and plant density, for the growth and production efficiency of organically grown hydroponic tomatoes under adverse environmental conditions in Qatar. The experiment used a split-split plot design with ‘Velocity F1’ and ‘Sigma F1’ as the main plot treatments and a factorial arrangement of grafting combinations and planting densities (3.5 and 5.5 plants/m2) as subplots. Tomato cultivar Velocity F1 grafted on Maxifort F1 resulted in greater vegetative growth and improved phenological attributes than nongrafted Velocity F1. Grafted ‘Velocity F1’ plants grown at 3.5 plants/m2 had an increase in leaf photosynthetic rates (18%), less transpiration loss (16%), and less electrolyte leakage (15%) while maintaining stomatal conductance and intercellular CO2 concentrations. At 9 weeks after transplanting, canopy growth was higher (24%) and flowering occurred earlier (3 days) with grafted ‘Velocity F1’ transplants than with nongrafted transplants. Higher fruit sets (20%), pollen viability (22%), and fewer flower drops (17%) were also observed for grafted ‘Velocity F1’ transplants than for nongrafted transplants. Marketable fruit yields were higher (26%) with grafted ‘Velocity F1’ grown at 3.5 plants/m2 than with nongrafted ‘Velocity F1’. Both grafted ‘Velocity F1’ and ‘Sigma F1’ fruits retained acceptable fruit color (L*, a*, b*, C*, °h), firmness, °Brix, titratable acidity, weight, and prolonged shelf life by 4 additional days than nongrafted ones. We conclude that grafted tomato ‘Velocity F1’ grown at a plant density of 3.5 plants/m2 was the best management strategy for enhancing seedlings quality, plant growth, and postharvest quality and alleviating abiotic stresses under this protected environment and hydroponic system.