Effects of an Ascophyllum nodosum seaweed extract application dose and method on growth, fruit yield, quality, and water productivity of tomato under water-deficit stress

Abstract

• We evaluated the effect of Ascophyllum nodosum seaweed extract (ASE) formulation on tomato under drought stress. • Tomato yielded more when ASE was applied at 5 mL L –1 as a soil drench than as a foliar spray. • Water productivity was maximized at 5 mL L –1 for all soil moisture levels. • Soil or foliar application of ASE at 5 mL L −1 could be regarded as an optimum dose. • ASE at 5 mL L −1 as a soil drench is more effective than its application as a foliar spray. The scarcity of irrigation water is a major threat restricting growth and productivity of almost all agronomic and horticultural crops. The tomato ( Solanum lycopersicum L.) is no exception. Seaweed extracts are widely used as biostimulants for the improvement of plant growth and development. Two independent pot experiments were conducted to find out the best soil drench or foliar spray dose of a commercial Ascophyllum nodosum seaweed extract (ASE) formulation (Amino Seaweed, SV Group, Bangkok, Thailand) on growth, physiological and biochemical parameters, fruit yield, quality, and water productivity of tomato under water-deficit stress. The commercial ASE formulation was applied in five doses (0, 2.5, 5, 10, and 20 mL L −1 ) as a soil drench (Experiment 1) or as a foliar spray (Experiment 2) under three soil moisture levels (50, 75, and 100% field capacity [FC]). Severe soil moisture deficit of 50% FC caused a 67 and 52% reduction in fruit yield, 11 and 11% reduction in fruit length, 25 and 29% decrease in leaf relative water content, while total soluble solids content was increased by 38 and 49% compared with 100% FC in Experiments 1 and 2, respectively. Soil drench or foliar spray of the commercial ASE formulation at 5 mL L −1 was effective at all soil moisture levels. Soil drench of the commercial ASE formulation at 5 mL L −1 resulted in 225% higher fruit yield in comparison to the untreated plants at 50% FC, whereas its application as a foliar spray resulted in 271% higher fruit yield in comparison to the untreated plants subjected to severe water-deficit stress (50% FC). Water productivity was found lower for the untreated plants regardless of soil moisture levels in both application methods; however, it was maximized at 5 mL L –1 for all soil moisture levels. The beneficial effects of 5 mL L –1 ASE formulation dose was also evident in physiological/biochemical traits and fruit quality of tomato regardless of application methods. Tomato yielded more when the commercial ASE formulation was applied at 5 mL L –1 as a soil drench (523.3 g plant –1 fruit yield) rather than as a foliar spray treatment (397.1 g plant –1 fruit yield). The results indicate that (i) 5 mL L −1 could be regarded as an optimum dose of the commercial ASE formulation for tomato applied either as a soil drench or foliar spray and (ii) exogenous application of the commercial ASE formulation at 5 mL L −1 as a soil drench treatment is more efficient, especially in fruit yield improvement, compared with its application as a foliar spray and, therefore, this technique holds promise for tomato cultivation under moderate water-deficit stress.