VENTURIA INAEQUALIS (CKE.) WINT. X. GROWTH RESPONSES OF BIOCHEMICAL MUTANTS

Abstract

THE EARLIER PAPERS of this series, which dealt chiefly with inheritance of pathogenicity in wildtype lines of Venturia inaequalis (Cke.) Wint. and in mutants that arose spontaneously in culture in vitro, have been summarized (Keitt, 1952). As the work on inheritance of pathogenicity advanced, the program was broadened to include correlated studies on the genetics, nutrition, and pathogenicity of this fungus. Beginning in 1950 chief attention was given to the induction and study of many biochemical mutants (Boone and Keitt, 1952; Boone et al., 1954, 1956; Keitt and Boone, 1954, 1955, 1957). It was shown that some of the mutations concerned had no apparent effect on pathogenicity, while others reduced or nullified it. Furthermore, in many cases in which pathogenicity had been lost on account of mutation the pathogenic reaction was restored, wholly or in large part, by supplying the required substances to the mutants during the incubation period (Boone et al., 1954; Kline, 1956; Kline et al., 1956). The materials and methods are thus available for studying in vivo aspects of nutrition of the fungus in relation to pathogenicity. In connection with these studies it was desirable to ascertain whether the induced nutritional deficiencies were partial or complete and to examine the range and extent of growth responses of the mutants to their required substances. Earlier studies on related aspects of the nutrition of V. inaequalis have been reported (Leben and Keitt, 1948; Pelletier and Keitt, 1954). This paper reports the quantitative growth responses of 12 representative biochemical mutants to varied concentrations of their required substances. Preliminary reports on this work have been made (Boone et al., 1954; Lamey, 1954). MATERIALS AND METHODS.-Biochemical mutants studied.-The 12 biochemical mutants used in this studv were derived from wild-type line 365-4 by treatment with nitrogen mustard or ultraviolet radiation (Boone et al., 1956). They require, respectively, choline (U-1905), pantothenic acid (U2584), nicotinic acid (U-2599), inositol (U-2694),