ISOZYME VARIATION AMONG BIOLOGICAL SPECIES IN THE GIBBERELLA-FUJIKUROI SPECIES COMPLEX (FUSARIUM SECTION LISEOLA)

lsozyme phenotypes were determined for 101 strains of Gibberella fujik uroi and 2 strains of Gibberella nygnmai that represent seven biologic al species (mating populations) isolated from a variety of plant hosts in dispersed geographic locations, Fourteen enzymes were resolved in one ol more of three buffer systems, Two of the enzymes, arylesterase and acid phosphatase, were polymorphic within two or more biological s pecies and are suitable for intraspecific studies of population variat ion, Six enzymes, alcohol dehydrogenase, aspartate aminotransferase, g lucose-6-phosphate dehydrogenase, mannitol dehydrogenase, phosphogluco mutase, and phosphogluconate dehydrogenase, were monomorphic in all of the isolates examined, The remaining six enzymes, fumarase, glucose p hosphate isomerase, glutamate dehydrogenase (NADP), isocitrate dehydro genase (NADP), malate dehydrogenase, and triose-phosphate isomerase, c ould potentially be used to distinguish the different biological speci es, Mating populations C and D are the most similar, since the mating population C isolates examined had the same isozyme phenotype as did a subset of the isolates in mating population D, Mating population E is the least similar to the other taxa examined, Unique isozyme phenotyp es are present but are composed of banding patterns shared among the b iological species, This finding supports the hypothesis that these bio logical species, with the possible exception of mating populations C a nd D, are reproductively isolated from one another and that no signifi cant gene how is occurring between them, Isozyme analysis is a useful method to distinguish these closely related biological species, Examin ation of isozyme phenotypes is more rapid than the present technique, which is based on sexual crosses; can be applied to strains that are n ot sexually fertile; and is more sensitive than traditional morphologi cal characters, which cannot distinguish more than three or four morph ological groups among the seven biological species, While emphasizing the discreteness of the mating populations as biological entities, our isozyme data also reaffirm the close genetic relationship among these groups.