THE OCCURRENCE OF A NEW GENETIC VARIANT OF FUSARIUM-OXYSPORUM FSP PISI

During a survey of root diseases of pea in Denmark, a new genetic variant of Fusarium oxysporum f.sp. pisi was isolated from vining peas in two widely separated geographical regions. In terms of pathogenicity on a set of differential pea lines, the Danish isolated closely resembled a race 6 isolate from the United States. DNA extracts of the isolates: restricted with the endonuclease HindIII, then probed with a homologous repetitive genomic fragment from the plasmid pDG106 by the Southern hybridization technique, gave a unique 'fingerprint' pattern distinctly different from the American race 6 and all other known races. When probed with pDG312, containing a homologous ribosomal repeat unit, the pattern obtained for the Danish isolates-was indistinguishable from races 1, 5 and 6 but distinctly different from 2A and 2B. The Danish isolates represent a separate vegetative compatibility group because they are compatible with each other but incompatible with the other known races. In pigmentation the new variant resembled races 1, 5 and 6 for the first 8-12 days, after which it began to secrete a dark purple pigment resembling that of race 2A and 2B. Until an additional line in the host differentials can separate the new genetic variant it should be considered a subgroup of F. oxysporum f. sp. pisi race 6.