Factors affecting systemic infection of tobacco by Peronospora tabacina

Economic crop losses in tobacco induced by Peronospora tabacina in the United States during 1980 were due in part to systemic plant infection. Controlled environment studies were conducted to assess the effects of site of infection, plant stress, and temperature on development of systemic infection. Results showed that systemic infection of apical meristematic tissue caused severe stunting. Lateral bud and stem infections did not produce dramatic stunting, and many infected plants appeared healthy. Lateral bud infections on nonstressed plants were the most difficult to diagnose. Similar plant growth rates occurred between plants with lateral or stem infections and healthy plants. Systemic infection occurred more readily at lateral buds than through the apical bud or stem. Plants stressed from transplant shock were more susceptible to systemic infection than plants that were not stressed. Colonization of the pathogen within the plant as measured by vascular necrosis was greater in nonstressed plants. Systemic symptoms developed at all temperatures tested. A significant temperature effect was observed only for rate of plant growth. Infected stem tissue did not support sporulation of the pathogen