A Modified Technique for Inducing Systemic Resistance to Blue Mold and Increasing Growth in Tobacco

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Abstract
Sporangial suspensions of Peronospora tabacina, aqueous washings from frozen or fresh leaves of uninoculated tobacco plants, washings from sporangia, ethanol-killed sporangia, autoclaved sporangia, or distilled water were injected into stems of 8- to 10-wk-old tobacco plants grown in the greenhouse. Injections were made either external or internal to the xylem. Plants injected external to the xylem with P. tabacina were systemically protected 90-99% (based on the area of necrosis and amount of sporulation) against disease caused by subsequent foliar challenge with the pathogen. Protection was about 50% 15 days after stem injection and reached a maximum after 21 days. Unchallenged plants injected with isolate 82 of the fungus were about 40% taller, had about 30% increase in fresh weight, about 40% increase in dry weight, four to six more leaves, and about 15% greater leaf area than control plants at the time the former reached 50% flowering. Plants injected with isolate 82 reached 50% flowering about 2 wk before the controls. Plants injected internal to the xylem were systemically protected against blue mold but were severely stunted.