Venturia Inaequalis (Cke.) Wint. Iv. Further Studies on the Inheritance of Pathogenicity

Parasitic and Biological Fitness of Venturia inaequalis: Relationship to Disease Management Strategies

“…Much of the early work in Europe (1,2,(67)(68)(69)(70)(71)(72)83,84), the United States (41,44,46,61), and Canada (39) demonstrated variability of the reaction of susceptible cultivars and crabapples toward V. inaequalis. More detailed investigations confirmed the earlier observations and studies: particular isolates attacked the cultivar from which they originated more severely than they attacked other cultivars (62,74,84).…”

“…Survival is threatened if the tree dies, because apple is an obligate outbreeder and each sibling growing nearby will have a unique combination of race-specific resistance genes that an ascospore can overcome only if it has a matching set of virulence genes. Crossing experiments in the 1940s (13,(40)(41)(42)44) using V. inaequalis strains with specific virulence to apple cultivars carrying differential resistances showed that new combinations of virulence genes do occur in ascospores and that the expression of pathogenicity (defined today as virulence) of the parasite is determined by host and pathogen genotypes. Thus, to increase the chance that a half-or full-sibling in the vicinity produced by the dead tree, or any other apple trees nearby, will be infected, the production of ascospores is the strategy that has assured survival.…”

The Relationship of Genes for Pathogenicity and Certain Other Characters in Venturia Inaequalis (Cke.) Wint

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EiVTURIA inaequalis (Cke.) Wint., the ascomycetous pathogen of apple scab, Yhas been shown to have adaptations similar to the eight-spored Neurospora species for use in genetic analyses (KEITT and LANGFORD 1941;SHAY and KEITT 1945;KEITT et al 1948;BOONE and KEITT 1956). I t has, in addition, two very important advantages over Neurospora: 1) I t is pathogenic and can be studied in vivo; and 2) it is uninucleate in its vegetative stage and, thus, is free from the confounding effects of heterocaryosis.

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