Baobabopsis donbarrettii RG Shivas, YP Tan & Thines

Description

Conidiophores emerging from stomata on the abaxial leaf blade surface, evanescent, aseptate, hyaline, cylindrical, 75-120 x 20-28 µm, with terminal ampulliform-lageniform branches 7-14 x 3-7 µm, with a narrow neck.

Conidia broadly ellipsoidal, 16-20 x 11-18 µm, hyaline, aseptate, slightly narrowed towards the base, deciduous. Germination not observed.

Oogonia formed in the leaf blades which split into a tangled mass of vascular fibres, subglobose, (27-)32-40(-45) x (25-)28-36(-39) µm in diameter, golden yellow; wall (exosporium including warts) 3-9 µm thick, uneven, densely verrucose with rounded warts.

Oospores one per oogonium, (19-)22-27(-29) x 20-25(-28) µm in diameter, subhyaline to golden yellow, wall (endosporium) 1-3 µm thick, even, smooth.

Hosts
   
Host family: Poaceae
   
Host species: Perotis rara - BRIP (holotype)

Distribution

WA

Comments

This downy mildew species has been found only in Australia, and is likely to be an indigenous fungus (Thines et al., 2015). The only specimen was collected on Perotis rara in 2011 near Kununurra in northern Western Australia. Baobabopsis differs from all other genera of Peronosporaceae in having broad club-shaped-cylindrical conidiophores with a cluster of terminal ampulliform projections bearing conidiaNo other downy mildew pathogen has been reported on Perotis throughout the world. The absence of an apical papilla on the asexual spores suggests that they do not germinate by releasing zoospores, rather by the production of one or more germ tubes (conidia).

Highslide JS
Baobabopsis donbarrettii on Perotis rara - BRIP 54675.
Scale bar = 1 cm. Healthy plant (left) and infected plant (right).
Highslide JS
Sporangiophore of Baobabopsis donbarrettii on Perotis rara - BRIP 54675.
Scale bar = 10 µm.
Highslide JS
Oospores of Baobabopsis donbarrettii on Perotis rara - BRIP 54675.
Scale bar = 10 µm.