Taxonomy of a fungus introduced into Hawaii for biological control of Ageratina riparia (Eupatorieae; Compositae), with observations on related weed pathogens

Abstract

Evidence is presented to show that the fungus, originally described as a species of Cercosporella (Hyphomycetes), introduced into Hawaii to control the composite weed Ageratina riparia, belongs to the white smuts (Ustilaginales). It is formally described as Entyloma ageratinae sp. nov. In addition to two external spore types (sporidia), which occur in prominent hypophyllous caespituli, hyaline, thin-walled, non-resting ustilospores are formed within non-necrotic leaf tissue. A further spore type, the spermatium, is abundantly produced from well-defined spermogonia. The significance of these previously unreported structures in the smut life-cycle is discussed.

Entyloma ageratinae was found to be present in the purported centre of origin of its weed host, the Jalapa (Vera Cruz) region of Mexico. Further collections of white smuts on other composite weeds (Parthenium hysterophorus, Melampodium divaricatum) in this locality are assigned to E. compositarum and compared with E. ageratinae. The additional discovery of Kordyana cubensis (Exobasidiales) on Commelina diffusa with a similar spermogonial state is reported and discussed in relation to the evolution of the Ustilaginales and Exobasidiales.