Self-fertility and other distinguishing characteristics of a new morphotype of Puccinia coronata pathogenic on smooth brome grass.

A new morphotype of Puccinia coronata, pathogenic to Bromus inermis, a common roadside and pasture grass in the northern United States, was discovered in the 1990s and described as P. coronata f. sp. bromi by Delgado et al in 2001. Puccinia coronata f. sp. bromi does not require fertilization of pycnia to produce aecia on its alternate host, whereas fertilization is required in all other varieties or formae speciales of P. coronata with aecial hosts in the family Rhamnaceae and for which life cycles have been described. Promycelia of P. coronata f. sp. bromi produce only two basidiospores, and each receives a pair of nuclei from the promycelium. The nuclei divide again so that mature basidiospores each contain four nuclei. Puccinia coronata f. sp. bromi has smaller teliospores than P. coronata var. avenae, and its substomatal vesicles are non-septate and distinctly shaped compared to those of P. coronata var. avenae. In addition, nuclei of P. coronata f. sp. bromi contain less DNA than those of P. coronata var. avenae. Puccinia coronata f. sp. bromi is further distinguished from P. coronata var. avenae and P. coronata var. hordei in being avirulent on both oat and barley, whereas neither P. coronata var. avenae nor P. coronata var. hordei are virulent on Bromus inermis.