Peronosclerospora sp. nov. 9

Description

Conidiophores not observed.

Conidia not observed.

Oogonia formed in the leaf blades which split into a tangled mass of vascular fibres, globose-subglobose, 26-44 µm in diameter, golden-brown, with smooth occasionally scabrid, flattened sides bordered by inconspicuous ridges ; wall (exosporium) 5-17 µm thick, reddish brown.

Oospores one per oogonium, globose, (19-)24-28(-35) µm in diameter, hyaline; wall (endosporium) 1-2 µm thick, hyaline, even, smooth.

Hosts
   
Host family: Poaceae
   
Host species:

Sorghum plumosum - BRIP


Distribution

NSW

Comments

This specimen was collected on Lizard Island which is approximately 100km north of Ciarns, Queensland. Although no host inflorescences were collected at the time, the site of collection (V. Boughton, personal communication; Byrnes et al. 1977) and comparison of the anatomy of the leaf blades with those of the closely-related Sorghum leiocladum strongly suggest that the host is Sorghum plumosum.

Several other Peronosclerospora species have been recorded on S. plumosum, namely P. australiensis RG Shivas, Ryley, Telle, Liberato & Thines (Shivas et al., 2012), P. miscanthi (Miyake) C.G. Shaw (Frederiksen and Renfro, 1977), P. philippinensis (Frederiksen et al. 1970) and P. sorghi (Bonde and Freytag, 1979). The morphology of the sexual state of the downy mildew fungus from Lizard Island does not match any of these described species with the oospore diameter being significantly smaller than those reported for the species australiensis, miscanthi and sorghi, and larger than those reported for P. philippinensis.

Ryley and Langdon (2001) suggested that the specimen may be assigned to P. noblei, an indigenous species found only on S. leiocladum. Recent molecular studies have demonstrated that the Lizard Island specimen belongs in a new species.