PATHOLOGICAL AND BIOCHEMICAL STUDIES ON Fusarium SPP. ISOLATED FROM FLAX ROOTS

Abstract

The high frequencies of Fusarium oxysporum and F. solani and their ability to cause considerable losses during seedling stage, strongly suggest that they are the most important pathogenic Fusarium spp. involved in the etiology of seedling blight and root rot of flax. Of seventy-three nonpathogenic isolates of Fusarium spp., twenty-seven (37%) showed antagonism (cross protection) against a highly pathogenic isolate of F. oxysporum. Flax cultivars and pathogenic isolates played a determinant role in the efficiency of cross protection. There was no association between susceptibility of cultivars to the pathogenic isolates and their response to the nonpathogenic isolates. On the other hand, cross protectionwas evidently more effective against the highly pathogenic isolates. Low concentrations of a nonpathogenic isolate resulted in the highest protection wheras high concentration did not result in protection. Thepathogenicity of 12 isolates of Fusarium spp. (8 isolates of F. oxysporum and 4 isolates of F. solani) was evaluated on 20 falx cultivars under greenhouse conditions. Analysis of variance (ANOVA) showed very highly significant (p=0.000) effects of cultivar, isolate, and cultivar x isolate interaction for preemergence damping-off, postemergence damping-off, and survival. In the case of dry weight, isolate was the only significant source of variation (p=0.000). Statistically significant interaction between flax cultivars and Fusarium isolates suggests that physiologic specialization exists within F. oxysporum and F. solani pathogenic on flax. AVOVA also implies that resistance of the tested cultivars is a mixture of both vertical and horizontal resistance and there are significant differences among cultivars in both types of resistance.