Eraphthora butleri (Weston) Telle and Thines

Synonyms

Sclerospora butleri Weston
Basidiophora butleri Thirumulachar and Whitehead

Description

Sporangiophores not observed on Australian specimens, but described by Thirumalachar and Whitehead (1952) as a simple, unbranched, obconical cell, narrow at the base, up to 22 µm long and 12 µm wide, with short apical pedicels bearing sporangia.

Sporangia not observed on Australian specimens but described by Thirumalachar and Whitehead (1952) as being lemon-shaped, 28-34 x 15-22 µm, deciduous, hyaline, germinating by release of motile, oblong-ellipsoidal zoospores 11 x 8 µm.

Oogonia formed in the leaf blades which split into a tangled mass of vascular fibres, globose-subglobose, 30-44 µm in diameter, pigmented; wall (exosporium excluding warts) 3-7 µm thick, with rounded hyaline warts 3-7.5 µm high, 4.5-6 µm at the base.

Oospores one per oogonium, adnate with the inner oogonium wall, spherical, (19-)22-27(-30) µm; wall (endosporium) 2-3 thick µm, hyaline, even, smooth.

Hosts
   
Host family: Poaceae
   
Host species:

Eragrostis cilianensis

   
  Eragrostis sp. - BRIP

Distribution

NSW, QLD

Comments

Comments

Molecular phylogenetic studies revealed that three specimens of a downy mildew on Eragrostis cilianensis collected in New South Wales were in the same clade as the type specimen of Eraphthora butleri, which was collected on an Eragrostis species in Italy (Telle and Thines, 2012).

A downy mildew fungus on Eragrostis has also been collected in western Queensland, but it was not examined in Telle and Thines’s study. The single specimen consisted of one tiller bearing a few frayed leaves, with the morphology of the oogonia and oospores adhering to these leaves being identical to those described for E. butleri (Weston 1933). Sclerophthora macrospora has also been reported on Eragrostis in the U.S.A. (Safeeulla, 1976) but it has much larger oogonia and oospores than E. butleri as well as a non-papillate oogonium wall (Shaw 1981). Two other graminicolous downy mildews, namely Peronosclerospora heteropogoni and Sclerospora iseilematis possess papillate oogonia, but the upper and lower limits of both species (Thirumalachar and Nariasimhan 1949; Siradhana et al. 1980) are much greater than the corresponding values for the Australian Eragrostis downy mildew pathogen. The conidiophores of P. heteropogoni and P. iseilematis are dichotomously branched, while those of E. butleri are simple, unbranched and club-shaped, with short apical pedicels each bearing a lemon-shaped sporangium (Thirumalachar and Whitehead 1952; Telle and Thines, 2012).  Based on the similarity of the sexual state of the Queensland specimen to that of the New South Wales specimens it is also regarded as a specimen of Eraphthora butleri, until examination of the asexual state or molecular studies prove otherwise.

Highslide JS
Eraphthora butleri on Eragrostis sp. - BRIP 2105.
Scale bar = 1 cm.
Highslide JS
Oospores of Eraphthora butleri on Eragrostis sp. - BRIP 2105.
Scale bar = 10 µm.