identification of fusarium species associated with sugar beet root in khorasan province and investigation of the pathogenicity of fusarium oxysporum

this study was carried out to identify fusarium species associated with sugar beet root rot and yellows. pathogenicity of fusarium oxysporum, the causal agent of fusariumyellows of sugar beet was also investigated. samples of infected roots were collected from fields in major sugar beet producing areas in khorasan province during 1999-2000. infected roots were washed, surface sterilised and plated on pda. one hundred sixty eight isolates of fusarium spp. were recovered. seven species were identified including fusarium solani (42 isolates), f. oxysporum (31 isolates), f. acuminatum (27 isolates), f.  avenaceum (23 isolates), f. moniliforme (19 isolates), f. equiseti (16 isolates) and f. culmorum (10 isolates). all isolates of f. oxysporum were tested for their pathogenicity on seedlings and matured sugar beet plants. the results showed that 12 isolates (38.7%) of f. oxysporum were non-pathogenic, and 19 isolates (61.3%) were  pathogenic.