Effect of the biostimulator Asahi SL on the mineral content of eggplants (Solanum melongenum L.) grown in an unheated plastic tunnel

Eggplants, known for their exceptional taste, are low in calories and constitute a rich source of potassium, phosphorus, magnesium, calcium, iron, manganese, copper and aluminum. They require a long and warm growing season, since adverse environmental conditions lead to growth inhibition, blossom fall and fruit drop. The application of eco-friendly biostimulators, such as Asahi SL, contributes to improving the growth and development of eggplants through increasing their stress tolerance and environmental adaptability, thus resulting in a higher yield. A two-factorial experiment in a split-plot design with three replications was conducted in 2010-2011. The leaves of two eggplant cultivars, Black Beauty and Violetta Lunga, were sprayed with a 0.1% solution of Asahi SL. Seedlings were grown in a heated greenhouse, in line with the generally observed standards for eggplant cultivation. Eight-week-old seedlings were planted in the ground, at 50x60 cm spacing, in an unheated plastic tunnel. Starting from 30 May, at 10-day-intervals, eggplants were sprayed three times with the biostimulator Asahi SL at a concentration of 0.1%. Plants sprayed with water served as control. The fruits were harvested at the stage of commercial maturity, when normal sized and colored but still unripe. The objective of this study was to determine the concentrations of macronutrients and micronutrients in fruits of two eggplant cultivars, grown in an unheated plastic tunnel and sprayed with the biostimulator Asahi SL. The mineral content of eggplants was determined in mid-August, on an average sample of marketable fruit yield collected in each treatment. The application of Asahi SL led to a significant decrease in total nitrogen levels in the fruits of cv. Black Beauty, and a significant increase in potassium concentrations in the fruits of both eggplant cultivars. The biostimulator increased Cu accumulation in fruits of both cultivars, and it significantly decreased Fe accumulation in cv. Violetta Lunga in comparison with the control treatment. The fruits of cv. Violetta Lunga harvested from control plants were characterized by normal Ca:Mg and Ca:P ratios. The broadest K:Mg ratio was noted in cv. Violetta Lunga in both treatments. The K:(Mg+Ca) ratio was higher in the fruits from control plants of cv. Black Beauty.