Relation of Soil Temperature and Nutrition to the Resistance of Tobacco to Thielavia basicola

Abstract

Five vars. of tobacco of different degrees of susceptibility to T. basicola were grown in sand in constant temp. tanks at 18-20[degree] and 28-30[degree]C. At each temp. half of the plants were given +N (nitrate N) nutrient soln. and half - N soln. For each condition some of the plants were inoculated with T. basicola and some kept uninoculated as controls. Roots and stem bases of some controls were wounded by pricking. The change in N nutrition did not alter the relative suscep-tibilities of the 5 vars. at high or low temps. High temps. decreased, low temps. increased, the amount of infection in both +N and -N plants. Microscopic examination of roots revealed no relation between peripheral periderm formation in controls, and degree of resistance. There was no evidence of the formation of a periderm in advance of the fungus or around fungal lesions. Response to fungal injury was similar to the reaction to mechanical injuries. Resistance to Thielavia under certain environmental conditions was apparently not detd. by anatomical modifications in the root and crown.