Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)


Plant Science

First Advisor

Michael W. Ferguson


Pathogenicity tests of different Fusarium spp. isolated from roots of wilted flax plants and flax seeds, showed that all pathogenic isolates were F. oxysporum. The nonpathogenic Fusarium spp. included F. moniliforme, F. solani, F. oxysporum and F. acuminatym. Cross protection tests of the nonpathogenic isolates of Fusarium spp. revealed that the large majority of the isolates which had outstanding cross-protective ability were E. oxysporum, and large differences in cross-protective ability were observed. Simultaneous inoculation of seven flax cultivars with a highly virulent isolate of F. oxysportm f.sp. lini and a nonpathogenic isolate of F. oxysporuron, significantly decreased the amount of wilt of all tested cultivars. However, the cultivars varied in the magnitude of their response to the cross-protective effect conferred by the nonpathogenic isolate. Similarly, the pathogenic isolates of E. oxysporuro f.sp. lini responded differently to the cross-protective effect of a nonpathogenic isolate of E. oxysporum. In general, the highly pathogenic isolates of F. oxysporum f.sp. lini were more responsive to cross protection than weakly pathogenic ones. The interaction between pathogenic isolates of F. oxysporym f.sp. lini, flax cultivars, and temperature was investigated. The results Showed that cultivar X isolate (P ≤ 0.001), cultivar X temperature (P ≤ 0.001), and isolate X temperature (P ≤ 0.001), were all very highly significant sources of variation. The cultivar X isolate X temperature interaction (P ≤ 0.01) was a highly significant source of variation. The effect of ineculum density on cultivar resistance, isolate virulence and their interaction was studied. The results indicated that, cultivar X inoculum, isolate X inoculum and cultivar X isolate X inoculum were all nonsignificant sources of variation. Analysis of inoculum density-disease incidence (ID-DI) relationships allowed interpretation of host-pathogen interaction as well as quantification of both cultivar resistance and isolate virulence. This analysis indicated that both.flax cultivars and pathogen isolates may differ only in the quantitative aspects of resistance and virulence and not in their biochemical pathways. Analysis of field data revealed that, cultivar X year was consistently a nonsignificant source of variation. On the other hand, cultivar X location interaction was either a significant (P ≤ 0.05), or very highly significant (P ≤ 0.001) source of variation with the exception of one data set. The amount of isozymic variation among isolates of F. oxysporum f.sp. lini is adequate for the application of numerical taxonomy on these isolates.

Library of Congress Subject Headings

Flax -- Disease and pest resistance Flaxwilt



Number of Pages



South Dakota State University