Effect of Shade Regimes and Plant Extracts on the Vegetative Growth and Yield of the Natural Sweetener Plant Stevia (Stevia rebaudiana Bertoni)

Abstract

A field experiment was conducted in the fields of the College of Agricultural Engineering Sciences / University of Baghdad in the spring of 2021-2022. Stevia (sugar leaf) seedlings propagated from tissue culture method of the Spanish variety Spanti were planted in the field on the mid of March, which were previously acclimated and 6 weeks old, with the aim of studying the role of shading and spraying some plant extracts on growth and leaf yield in sugar leaf (stevia) plant. Randomized Complete Bock Design (RCBD) with three replications was used, using split plot arrangement. The experiment included two factors, the main factor includes two levels of shading, the first without shading (exposed) and the second 50% shading and they are denoted S1, S2 respectively, and the secondary factor is spraying with aqueous plant extracts of Moringa at a rate (10%) and (15%), denoted M1 and M2 respectively, and licorice extract at a rate (3%) and (6%), denoted G1 and G2 in addition to the M0G0 control treatment which was sprayed with distilled water on three dates, 15 days after establishing, 30 and 45 days from planting and measurements are taken after each spray. The results showed that S2 was significantly superior to S1 in terms of plant height (68.87 cm), and in the number of leaves branches-1 at (232.72 leaves branch-1), while S1 was significantly superior to S2 in number of branches (8.53 branches plant-1) and number of leaves (1674.80 leaves plant-1) and in leaf area (246.84 dm2 plant-1) as well as in dry weight of leaves (41.49 g plant-1). While M2 was significantly superior in plant height (65.51 cm), followed by G2 (64.55 cm) and also excelled in the number of leaves branches-1 (234.20 leaves branch-1) followed by G2 (225.65 leaves branch-1). The G2 extract also outperformed significantly in number of leaves (1358 leaves plant-1) followed by M2 (1317.50 leaves plant-1) and M1 (1309 leaves plant-1) and in dry weight of leaves (38.21 g plant-1), followed by G2 (36.30 gm plant-1), which was significantly superior in leaf area (217.30 dm2 plant-1), while in terms of number of branches, G1 treatment was superior with 6.42 branches plant-1. As for the interaction between the study factors, it showed that spraying M2 extract on exposed plants S1 gave the largest leaf area and highest dry weight for stevia plant, and also showed the same concentration M2 highest plant height and highest percentage of number of leaves branche-1 for stevia plant when sprayed on shaded plants S2 under the conditions of the central region of the country.