Puccinia rugispora: An unusual microcyclic rust endemic to Hawaii

Abstract

Puccinia rugispora, a recently-described microcyclic rust on the endemic forest tree Zanthox- ylum dipetalum (Rutaceae) in Hawaii, forms telia deep within the leathery leaf tissue of its host. Telio- spores exhibited unusual germination behavior by production of a sequence of two spherical vesicle-like germination structures from each cell rather than germ tubes or elongate metabasidia as in most rusts. A sterigma bearing a basidiospore was produced on one or both of the globoid segments. Direct produc- tion of a germ tube from the distal-most segment of the germination structure at times also was observed. Karyogamy occurred in the young teliospore, fol- lowed by migration of the nucleus into the germi- nation structure, where one or more mitotic divisions provided one or two large diploid nuclei for each segment. One of the nuclei migrated into the devel- oping basidiospore and underwent meiosis, produc- ing four small nuclei in the basidiospore. Whereas this behavior is atypical of the rusts in general, it agrees with unusual teliospore germination and nu- clear behaviors observed in other Hawaiian rusts which have evolved with their hosts in isolation from continental forms.