Stem infection of tobacco plants with three strains of Peronospora tabacina Adam

Abstract

The pathogenicity of three strains of Peronospora tabacina Adam., APT1, APT2, and APT3, in stems of tobacco plants and their effect on the development and survival of plants were determined.

(1) APT1, APT2, and APT3 are highly pathogenic in stems of cv. Virginia Gold and in two varieties of Oriental tobacco. Stems of cv. SO1 plants (resistant line) are unaffected by the original strain APTl but are severely infected by the two new strains APT2 and APT3.

(2) Severe stem infection developed in injected plants at a temperature of 15–25°C and R.H. higher than 80°. Mycelium of the pathogen rapidly invaded all stem tissues. Of affected plants, 40–75% were killed and the survivors remained dwarfed with small and severely wilted leaves. Under humid and cool conditions APTl and APT3 were more destructive than APT2.

(3) Mild stem infection developed at a temperature of 20–30°C and R.H. not higher than 70%. Under these conditions APT2 was more pathogenic than APTl or APT3. The mycelium of the fungus was associated mainly with the vascular system. General plant growth and leaf areas were only slightly reduced.

(4) It is concluded that present methods of controlling blue mould in tobacco plants need extension. Consideration should be given to breeding for resistance to stem infection with due regard to the two new strains of P. tabacina described in this paper and the probable occurrence of further physiologic strains of this pathogen in the future.