THE SPECIES CONCEPT IN FUSARIUM WITH REFERENCE TO SECTION MARTIELLA

Abstract

THE PLANT pathologist and mycologist are confronted continually with the problem of identifying the widely distributed members of the genus Fusarium, so frequently associated with the disorders of plants. Among the Fusaria most frequently found in such associations, some as virulent parasites and some as saprophytes, are the three species, seven varieties and three forms grouped by Wollenweber and Reinking (1935) into the section Martiella of this genus. In addition to these imperfect fungi, two species of Hypomyces, with their three varieties and one form, are included in the section. Therefore, one who is confronted with the task of identifying a member of section Martiella must compare his fungus with the two genera, five species, ten varieties and four forms established in the above (and only) taxonomic treatment heretofore available for this section. Wollenweber and Reinking distinguish F. coeruleum (Lib.) Sacc. from the other two Fusarium species, F. solani (Mart.) App. et Wr. and F. javanicum Koord., on the basis of a relatively slight difference in the degree of curvature at the base of the macroconidia. F. solani is distinguished from F. Javanicum by the width of 3to 5-septate conidia, which is 5 to 6 microns in the former and 4 to 5 microns in the latter species. However, varieties of F. solani are listed which have widths between 4 and 5 microns. Further differentiation between these species is based on spore length, colony appearance and pigmentation, and the relative bluntness of the apical cell. The average dimensions of the 3and 5-septate conidia of the three Fusariurm species of the section are as follows: