Cultural Morphology and Sexuality of Inonotus arizonicus

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Abstract
I. arizonicus (Aphyllophorales: Hymenochaetaceae) causes a white heart rot of Arizona and California [USA] sycamores [Platanus wrightii] and is known only from the Southwest in these hosts. I. arizonicus fruits readily in culture, and basidiospores give rise to single-spore isolates that also fruit and sporulate. Basidiocarps from single-spore isolates are morphologically identical macroscopically and microscopically to those that develop from presumptive heterokaryons derived from basidiocarp-tissue isolates and mass-basidiospore cultures. As all members of the Hymenochaetaceae, I. arizonicus lacks clamp connections. Preliminary cytological investigations of nuclear state showed no differences between single-basidiospore isolates and tissue isolates. These observations strongly suggest that I. arizonicus is homothallic. Presumptive heterokaryotic tissue isolates from different localities produce a dark interaction zone when grown on the same plate or in wood test blocks. Homozygous matings do not form an interaction zone. Agar-block decay tests show that single spore isolates show no appreciable differences in decay capacity from tissue isolates. I. arizonicus readily decays wood of several associated species (Arizona ash, Arizona black walnut, southwestern chokecherry and netleaf oak) in standard wood test blocks although it does not occur on these hosts in nature.