First fruit in season: seaweed extract and silicon advance organic strawberry (Fragaria×ananassa Duch.) fruit formation and yield

Environmentally-conscious organic strawberry fruit producers are mostly cultivating plants in non-heated greenhouses and striving to produce fruit early in season. Several strategies have been proposed to advance strawberry fruit formation, among them the use of seaweed extract in combination with silicon. The aim of the present research was to evaluate the potential of Ascophyllum nodosum seaweed extract and silicon for early-cropping of organic strawberry cv. 'Clery' grown in a non-heated greenhouse. Strawberry reproductive performance (the number of fruits per plant, individual fruit mass and fruit yield per plant) was monitored on six harvest dates. Additionally, internal fruit quality (primary and secondary metabolites) was assessed with the aid of high performance liquid chromatography/mass spectrometry (HPLC/MS) on the first four samplings. Foliar application of biostimulants resulted in a significant increase of early fruit yield, total fruit yield and total number of fruit in season with ca. 20% less sugar and a lesser content of phenolics BA and HA at the first harvest date. Differences in sugars, organic acids and most phenolic compounds were less uniform during the season but early-fruit was characterized by higher levels of anthocyanins. The use of biostimulants in strawberry production is justified as the products stimulate generative development of strawberries, which produce 10% more marketable yields earlier in season.