Peronosclerospora sacchari (T. Miyake) Shirai & Hara

Synonyms

Peronosclerospora sacchari (T. Miyake) C.G. Shaw
Sclerospora sacchari T. Miyake
Sclerospora sorghi-vulgaris Mundk.

Description

Conidiophores not observed on Australian specimens, but described by Waterhouse (1964) as arising from stomata mostly on the abaxial leaf blade surfaces, evanescent, 160-170 µm long in total, main axis 8-13 µm in diameter up to a septum 68-110 µm from the base then increasing to 20-34 µm wide at the start of the branches; branch system 70-130 µm high and 100-130 µm wide, dichotomous, with 2-4 primary branches then secondary, tertiary and quaternary branches, each terminating in a tapering pedicel 10-15 µm long.

Conidia not observed on Australian specimens, but described by Waterhouse (1964) as being borne singly at the tips of pedicels, ellipsoidal-ovoid-cylindrical, 25-54 x 15-23 µm, hyaline, aseptate, without operculum or pore, germinating by one or two germ tubes.

Oogonia formed in the leaf blades, irregularly elliptical, 55-73 x 49-58 µm in diameter, golden-brown, forming several folds on the wall.

Oospores one per oogonium, globose, 40-54 µm in diameter, yellow; wall (endosporium) 2-4 µm thick, hyaline, even, smooth.

Hosts
   
Host family: Poaceae
   
Host species:

Saccharum officinarum - BRIP 51327 (PNG)

   
  Saccharum robustum - BRIP 47022 (PNG)
   
  Saccharum spontaneum BRIP 53578 (PNG)
   
  Saccharum sp. - BRIP 44241 (East Timor)
   
  Zea mays - BRIP 2104 (QLD; could be P. australiensis)

Distribution

QLD

Comments

Peronosclerospora sacchari is a systemic pathogen of sugarcane (Saccharum officinarum), causing a mottling of emerging leaves followed by the development of longitudinal chlorotic stripes between the vascular bundles often across the entire width of expanded leaf blades. A white down consisting of conidiophores bearing conidia develop at night on the abaxial leaf surfaces opposite the chlorotic streaks and occasionally in the streaks on the adaxial surfaces. Sporulation develops first near the tips of the leaf blades, progressing gradually towards the ligule on successive nights. The oogonia and oospores develop in the chlorotic tissue during the late Autumn-winter months (May-September) in Australia ultimately causing shredding of the leaves Leece (1941). Downy mildew-infected tillers bearing such leaves are often taller than healthy tillers, bearing fewer and shorter leaves. Based on circumstantial evidence from the results of planting a range of grasses adjacent to sugarcane crops infected by P. sacchari, Leece (1941) suggested that maize and teosinte (Euchlaena mexicana) were also hosts of the fungus, but no specimens of P. sacchari on these hosts exist. P. sacchari has been eradicated from Queensland (Simmonds, 1966), but key sugarcane germplasm is still tested for resistance to the pathogen in Papua New Guinea (Sugar Research Australia, 2015).

Highslide JS
Peronosclerospora sacchari on Saccharum sp. - BRIP 44241.
Scale bar = 1 cm.
Highslide JS
Oospores of Peronosclerospora sacchari on Saccharum sp. - BRIP 44241.
Scale bar = 10 µm.