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Vegetative compatibility groups (VCGs) of 52
isolates of Fusarium oxysporum f. sp.
melonis (Fom), races 1
and 1,2 and 241 isolates of F. oxysporum from weeds which were
nonpathogenic to Cucumis melo cultivars
using nit (nitrate non-utilizing) mutants were
studied. Eighty five nit mutants were synthesized
from Fom isolates and their phenotypic
classes on medium containing sodium nitrate,
sodium nitrite, hypoxanthin, ammonium
tartrate and uric acid were investigated. Tne
mutants were grouped in to nit 1 (66%),
nit 3 (19%) and nit M (15%). nit mutants were
crossed on minimal medium with
standard nit mutants 0134-0137 (T. Gordon).
AllIranian Fom isolates formed strong
heterokaryon reaction only with 0134. There was
no correlation between VCGs and
races, geographic origin and host of Fom.
Two hundred and one nit mutants of nonpathogenic
isolates of F. oxysporum were
crossed with standard mutants 0134-0137and nit
mutants of Fom isolates No reaction
was observed. Ninteen vcas were found among
nonpathogenic isolates of F. oxysporum
when nit M mutants were crossed with nit 1 and
nit 3 mutants of the isolates.