Stevia (<i>Stevia rebaudiana</i> Bertoni): Biological Properties and Factors Affecting Plant Growth and Sweet Glycosides Accumulation
Stevia rebaudiana Bertony is well known because its leaves contain diterpene steviol glycosides. The main of them are stevioside and rebaudioside A, both have a sweetness about 250-350 times higher than sucrose and, hence, are popular natural low-calorie sugar substitutes in foodstuffs. Due to the complex biochemical composition of its leaves, stevia is also a pharmacologically and cosmetically valuable plant: its leaf extracts exhibit very high antioxidant properties comparable to those of green tea. This article is a detailed and up-to-date overview of the available data on the biological characteristics of stevia cultivars, as well as on a variety of factors affecting stevia growth, dry leaf yield, and steviol glycosides accumulation. The study is of practical interest to the agricultural industry: stevia has the potential to turn into a major crop in Russia as many regions here have growth conditions favorable to obtain high yields of ecologically safe stevia products (dry leaves of the best quality and sweet glycosides); using these products in the food industry will improve the public health. However, the Russian literature on stevia poorly covers the latest findings on how stevia depends on some key factors, such as genotypes, environment (soil and climate conditions, light intensity, temperature), diseases and pests, etc., thereby holding back the advance of agricultural technologies for growing stevia in Russia. The results obtained define and summarize the exact conditions necessary for obtaining high yields of stevia dry leaves and sweet glycosides, as well as the factors that must be taken into account both in industrial cultivation and in scientific research of stevia.