Study of the Variety Reaction of Stevia Selection Materials to Alternaria alternata on Natural Background of Infection

Abstract

 Stevia is a perennial bushy plant of the Asteraceae family originating from Northeastern Paraguay. Today, its cultivation has spread to other regions of the world, including Canada and some parts of Asia and Europe. It is also introduced successfully in the conditions of our country. Sweetness of the stevia leaves exceeds many other high-potential sweeteners and probably in the future stevia will become a major source of natural sweetener for the growing market of organic foods. In the literature are described many diseases affecting stevia, caused mainly by the pathogens of the genera – Phomopsis, Phlyctaena, Alternaria, Septoria, Rhizoctonia and others. For now the most widespread in Bulgaria is the brown leaf spot (Alternaria alternata) disease. The purpose of this study was to determine what is the reaction of different stevia origins to brown leaf spot disease and the influence on the yield. The survey examined 16 stevia origins of the selection gene pool of Agricultural Institute – Shumen. Planting is done in early May at above 10ºC of the soil. From the study it was found that: Morbidity of the studied genotypes was 14.4%, ranging from 1 to 15 plants of each origin. In natural background of infection the most productive origins are 210/9, 7E and 9E. The origins 4E and 404/7 are highly susceptible to Alternaria alternata. The potential loss of the main raw material (dry leaves mass) from the entire experimental field is 3.35 kg or 210 g of each variant.