Inheritance of Naphthazarin Production and Pathogenicity to Pea inNectria haematococca

Abstract

A naphthazarin-producing (fusarubin, novarubin, javanicin, norjavanicin), highly pathogenic strain of Nectria haematococca (sexual state of Fusarium solani var. martii) was crossed with a non naphthazarin-producing, slightly pathogenic mutant strain. This cross and several backcrosses were studied by unordered tetrad analysis. In all tetrads a 4:4 ratio of naphthazarin-producing ascospore strains to non-naphthazarin producing ones resulted. By two-factor analysis for this character and the markers determining mating type, sexual type, colonial growth, and perithecial colour respectively, parental-ditype, non parental-ditype, and tetratype tetrads resulted. This indicates that the loss of the capacity to produce naphthazarins is due to a mutation at a single locus, which probably blocks the biosynthesis of a polyketide precursor. When the same tetrads were tested for pathogenicity, the strains could not be classified into a group with high pathogenicity and one with low pathogenicity, as they showed intermediate degrees of pathogenicity. It is therefore concluded that the degree of pathogenicity is polygenically inherited. The difference in the inheritance of the capacity to produce naphthazarins and of pathogenicity, as well as the appearance of highly pathogenic though non-naphthazarin-producing segregants, indicates that the capacity to produce novarubin, fusarubin, javanicin, and norjavanicin is not a major factor in