Soil as a factor in the incidence of Peronospora tabacina Adam on tobacco

Abstract

(1) Plants of a flue-cured variety of tobacco (cv. Virginia Gold) were grown on several soils and subjected to attack by P. tabacina. (2) Leaves of plants grown in soils high in organic matter were large, soft, and succulent and retained the juvenile phase of susceptibility to attack by P. tabacina. Leaves with similar characteristics were not produced following addition of nitrogen to soils low in organic matter. (3) Severity of disease increased during the period of delayed leaf maturity caused by addition to the soil of nitrogen in excess of that required by flue-cured tobacco plants. (4) Soils high in organic matter or in added nitrogen are unsuitable for the growth of flue-cured tobacco, and plants grown in the former are more susceptible to P. tabacina than those grown on the latter. Under field conditions tobacco plants grown on pasture land or on other soils that arc also high in organic matter arc very susceptible to P. tabacina and can be the source of infection for crops grown in a wide area.