The range in cultural variability of Fusarium oxysporum f. cubense on potato dextrose agar was studied. Several hundred isolates obtained from diseased varieties of Musa were categorized into four morphological groupings or cultivars. These were termed 'Sporodochial', 'Ropy', 'Cottony Alba', and 'Slimy Pionnotal'. The morphological cultivar 'Sporodochial' was further divided physiologically into 'Odoratum' and 'Inodoratum' cultivars. Clones producing sporodochia were the parental forms from which all other cultural types could arise by mutation. Mutants did not revert to their parental types. A system is proposed for cataloguing clones of plant pathogenic Fusarium species. Based on morphological characters, the catalog is intended to serve as a collection of data which provides also for the categorizing of cultivars.

Two naturally occurring races of the Fusarium wilt or Panama disease fungus, F. oxysporum f. cubense (E.F.S.) Snyd. and Hans., have been identified. Race 1 is world-wide in distribution and attacks certain AAA triploids of Musa acuminata, of which variety 'Gros Michel? is the most important, and Musa textilis. Race 2 has been identified in Honduras, El Salvador, Puerto Rico, Virgin Islands, and the Dominican Republic and attacks certain ABB triploids of M. acuminata × M. balbisiana known as 'Chato', 'Bluggoe', 'Rulo', or 'Chamaluco'. Both races are pathogenic on 3- to 4-month-old seedlings of M. balbisiana, M. schizocarpa, and M. acuminata ssp. banksii, but the race 2 clone was less pathogenic than the race 1 clones tested. Mature M. balbisiana is immune to rhizome infection in the field. 'Odoratum' and 'Inodoratum' cultivars of F. oxysporum f. cubense are found within race 1; only the 'Inodoratum' cultivar is found within race 2. Circumstantial evidence indicates an independent development of race 2 in different areas. Race 2 wilt-susceptible ABB triploids hybridize and set seed with pollen from diploid M. balbisiana (BB) and M. acuminata (AA), the two ancestors of the cultivated banana. This will facilitate a study of the inheritance of wilt resistance to F. oxysporum f. cubense races 1 and 2.