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

Description

Conidiophores none observed.

Conidia none observed.

Oogonia formed in the leaf blades which split into a tangled mass of vascular fibres up to 50 cm long, globose-subglobose-ellipsoidal-irregularly polyangular, (55-)58-68(-76) µm in diameter, golden orange–yellowish or reddish brown; wall (exosporium) 2-15 µm thick, uneven, smooth, convoluted.

Oospores one per oogonium, globose or broadly ellipsoidal, (39-)43-51(-55) µm in diameter, often with a large vacuole; wall (endosporium) 2-5 µm thick, even, smooth.

Hosts
   
Host family: Poaceae
   
Host species:

Sorghum plumosum - BRIP

   
  Sorghum timorense - BRIP (holotype), , , , , , , , , , , , , ,
   
 

Sorghum sp. - BRIP

   
  Zea mays - BRIP , , , , , , , , , ,

Distribution

NT, WA

Comments

This downy mildew fungus has been identified on two wild, indigenous species of Sorghum, namely S. plumosum and S. timorense and on maize in the tropical region of northern Western Australia. Molecular phylogenetic analysis has shown that two specimens of maize from the Northern Territory were part of a clade which included the type specimen of P. australiensis and specimens on Sorghum plumosum (Telle et al., 2010). Shivas et al., (2012) provided a brief description of conidiophores and conidia found on the lower leaf surfaces on one of the maize specimens; the conidiophores were dichotomously branched and the spores were globose, subglobose to broadly ellipsoidal, 16-24 x 16-24 µm and germinated by a germ tube. This observation suggests that the asexual spores are conidia, and confirms that this species belongs in Peronosclerospora.

Ramsey and Jones (1988) documented several detections of downy mildew on maize and sweet corn across northern Western Australia, the Northern Territory and Queensland prior to 1988, which were variously attributed to either Peronosclerospora maydis or P. sorghi, two of the most serious downy mildew pathogens of maize and grain sorghum (Sorghum bicolor). Recent molecular studies have confirmed that many of these outbreaks on maize (Ord River, Western Australia, 1981; Atherton Tablelands, Queensland, 1985, 1986, 1987. 2016; Booroloola, Northern Territory, 2005) were due to P. australiensis. Ramsey and Jones (1988) successfully inoculated maize plants with conidia of the downy mildew fungus that they found on plants of S. plumosum growing near sites of the DM outbreaks on maize. The most likely source of inoculum for many of these maize DM outbreaks in northern Australia was conidia from S. plumosum and perhaps S. timorense.

This Peronosclerospora species has been reported only from Australia, but may later be found in parts of SE Asia where S. plumosum and S. timorense grow.

Highslide JS
Peronosclerospora australiensis on Sorgum timorense - BRIP 49816.
Highslide JS
Peronosclerospora australiensis on Sorgum timorense - BRIP 46736.
Scale bar = 5 cm.
Highslide JS
Oospores of Peronosclerospora australiensis on Sorgum timorense - BRIP 49819.
Scale bar = 100 µm.
Highslide JS
Oospores of Peronosclerospora australiensis on Sorgum timorense - BRIP 46736.
Scale bar = 10 µm.