A comparative morphological and physiological study of a number of strains of Botrytis cinerea Pers. with special reference to their virulence

Abstract

Summary (1) The growth features of three strains of Botrytis cinerea were examined on a variety of media. One strain (Sc) proved to have a strongly marked sclerotium-forming tendency, strain M showed a general tendency towards the development of aerial mycelium, and strain Sp was characterised by its freely sporing habit. (2) The intensity with which the various characters were manifested varied somewhat from medium to medium, but the general tendencies as noted above were observable throughout. (3) The effect of high atmospheric humidity was to increase the tendency to sclerotium formation and to diminish the tendency to sporulation. A similar effect produced by absence of light was indicated. (4) A definite difference in spore size and shape was shown as between strain Sp on the one hand and strains Sc and M on the other. (5) On the majority of media tested, strain Sc differed from the other two in showing a much slower rate of growth. (6) Inoculation experiments with a number of host plants showed that strain M was the most actively parasitic. No evidence of selective parasitism was obtained. (7) An analysis of the factors responsible for the differences in virulence observed was attempted. As far as the data could be interpreted, it was shown that the varying degree of virulence could not be ascribed to varying capacities of the strains for secreting the pectinase enzyme. It also appeared that the differences in parasitic power shown by the three strains could not be explained on the basis of different powers of mechanical penetration. A test of the three strains in the latter respect showed that they all possessed approximately the same penetrative power as judged by their behaviour on a series of formalised gelatine membranes of graded hardness.