Puccinia rugispora: An unusual microcyclic rust endemic to Hawaii

Abstract

Puccinia rugispora, a recently-described microcyclic rust on the endemic forest tree Zanthoxylum dipetalum (Rutaceae) in Hawaii, forms telia deep within the leathery leaf tissue of its host. Teliospores 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 production of a germ tube from the distal-most segment of the germination structure at times also was observed. Karyogamy occurred in the young teliospore, followed by migration of the nucleus into the germination structure, where one or more mitotic divisions provided one or two large diploid nuclei for each segment. One of the nuclei migrated into the developing basidiospore and underwent meiosis, producing four small nuclei in the basidiospore. Whereas this behavior is atypical of the rusts in general, it agrees with unusual teliospore germination and nuclear behaviors observed in other Hawaiian rusts which have evolved with their hosts in isolation from continental forms.

Key Words:

• endemic species
• Hawaiian rusts
• nuclear behavior
• teliospore germination