Relationships between Cultural Characters and Pathogenicity in Venturia inaequalis and

SUMMARY: Series of experiments were carried out both in witro and in vivo on single conidial isolates of Venturia inaequalis and V. pirina. Relationships between colony type and sporulation in vitro were apparent in both species. In addition, isolates of V. inaequalis showed relationships between degree of resistance of host source, width of host range and stability of cultural characters and pathogenicity during storage in culture. Isolates of V. pirina showed no such relationships, cultural characters being invariably stable while pathogenicity rapidly declined in the storage conditions. Studies of nutritional requirements suggested no deficiencies in the synthetic abilities of either pathogen, but limiting nutritional factors were im-portant. Isolates of both species which differed widely in pathogenicity and other characteristics, reacted similarly to various culture media. The use of Venturia inaequalis (Cke.) Wint. as a test organism for the labora-tory evaluation of protective fungicides for use against the apple and pear scab diseases (Montgomery & Moore, 1938) requires the provision of a routine supply of conidia over long periods. Much difficulty has been experienced i