Ultrastructure and ornamentation of Puccinia carduorum urediniospores and teliospores

Abstract

Scanning and transmission electron microscopy were used to describe the nature and mode of development of surface ornamentation of urediniospores and teliospores of Puccinia carduorum produced on Carduus thoemeri. Spines (echinulations) were restricted primarily to the apical ⅔–¾ of urediniospores. The basal of the spore surface was devoid of spines except for two, small, distinct zones; those were: (i) numerous small spines within the hilum region encircled by (ii), a single, or sometimes double, ring of larger spines distributed around the base of the spore, located approximately where the spore surface was previously contiguous to the perimeter of the pedicel apex. The ring of large spines and the small spines within the hilum region perhaps facilitate separation of the spores from the pedicels. All types of urediniospore spines observed appeared to follow a developmental path similar to that described in other rusts. Urediniospores having thicker walls than typical urediniospores were often observed, although the distribution of spines was similar on both types of urediniospores. Teliospores were covered with numerous, short, wart-like verrucae having similar electron opacity as the rest of the spore wall. Prior to their appearance on the surface of mature teliospores the verrucae were present within the matrix of the wall of immature teliospores.