Peronosclerospora sargae RG Shivas, Ryley, Telle, Liberato & Thines

Description

Conidio/sporangiophores not observed.

Conidia/sporangia not observed.

Oogonia formed in the leaf blades which split into a tangled mass of vascular fibres up to 30 cm long, globose-subglobose-ellipsoidal-occasionally irregularly polyangular, (30-)33-43(-47) µm in diameter, pale yellow-yellowish brown; wall (exosporium) 2-8 µm thick, uneven, smooth.

Oospores one per oogonium, globose, (24-)26-32(-34) µm in diameter, often with a large vacuole; wall (endosporium) 1.5-3 µm thick, even, smooth.

Hosts
   
Host family: Poaceae
   
Host species:

Sarga sp. -

   
  Sorghum timorense - BRIP (holotype)

Distribution

NT

Comments

Despite the absence of the asexual state in herbarium specimens, Telle et al., (2010) reported that analyses of partial cox2 and nrLSU sequences showed that the type specimen of P. sargae was closely aligned to, but phylogenetically distinct from, other described species of Peronosclerospora on sorghum, including P. australiensis. Also, the oospores of P. sargae are larger than those of P. noblei. Sorghum timorense, the only known host of P. sargae is indigenous to Australia, Timor and perhaps other islands in the Malesia floristic zone, so it is quite possible that its downy mildew fungus is not restricted to Australia.

Tall, vegetative tillers up to 3 m high and bearing fraying leaves with adhering oogonia are the diagnostic symptoms of downy mildew-infected plants of S. timorense. The mode of infection of this annual grass by P. sargae is unknown.
Highslide JS
Oospores of Peronosclerospora sargae on Sorghum timorense - BRIP 27691.
Scale bar = 10 µm.