Peronosclerospora eriochloae Ryley & Langdon
Peronosclerospora globosa Kubicek & R.G. Kenneth nomen nudum
Conidiophores emerging from stomata on the abaxial and adaxial surfaces of chlorotic leaf blades, evanescent, 245-280 µm long in total, main axis swollen at base and 6-13 µm in diameter gradually decreasing to 6-9 µm wide at a septum 90-115 µm from the base then increasing to 20-30 µm wide at the start of the branches; branch system 45-100 µm wide, dichotomous, with secondary, tertiary and quaternary branches, terminating in conoid-subulate pedicels 4-9 x 3-4 µm.
Conidia borne singly at the tips of pedicels, evanescent, globose-subglobose, (9-)12-14(-18) x (9-)10-12(-14) µm, hyaline, aseptate, without operculum or pore, germinating by one or two germ tubes.
Oogonia formed in the leaf blades which split into a loose mass of vascular fibres, globose-subglobose, surface smooth, polyangular (33-)40-53(-70) µm in diameter, orange-luteus; wall (exosporium) 3-17 µm thick, reddish brown.
Oospores one per oogonium, globose, (27-)30-37(-46) µm in diameter, hyaline; smooth; wall (endosporium) 2-3 µm thick, hyaline, even, smooth.
Although Kubicek and Kenneth (1984) briefly described a new downy mildew fungus (Peronosclerospora globosa) on several Eriochloa species in Texas, USA, they never validly published the name according to rules of the International Code of Botanical Nomenclature. During a study of systemic fungi on perennial grasses, Ryley and Langdon (2001) found a downy mildew fungus on early spring grass (Eriochloa pseudoacrotricha) at several locations in southern Queensland. Investigations revealed that hyphae of the fungus perennated in tiller bases of the grass during the winter months and invaded some of the tiller buds in early spring. Tiller buds that were not invaded developed into healthy, flowering tillers whilst invaded tiller buds developed into systemically infected, vegetative tillers bearing chlorotic leaves on/in which the asexual and sexual states developed in succession (Ryley 1985, 2001, 2002; Ryley and Langdon 2001). As the fungus differed in morphology from all described species of Peronosclerospora, Ryley and Langdon (2001) named the fungus Peronosclerospora eriochloae. A specimen of a downy mildew fungus infecting Eriochloa crebra in New South Wales had characteristics identical to those of P. eriochloae.
In 1995, a limited outbreak of downy mildew on one maize line amongst many others in a breeder’s nursery southern Queensland was attributed to an unknown species of Peronosclerospora, possibly P. maydis. Telle et al., (2010) used DNA sequence analysis to show that the causal fungus was actually P. eriochloae, which had not previously been recorded on maize. Early spring grass is known from the immediate vicinity of the downy mildew outbreak, so it is highly probable that conidia of P. eriochloae that developed on downy mildew-infected plants of E. pseudoacrotricha were the inoculum for the infection of the highly susceptible maize breeding line during a period of conducive weather. A fungus found on Panicum laevinode in New South Wales was co-located within the P. eriochloae clade (Telle et al., 2010).
The record of a species of Peronosclerospora on Eriochloa spp. in the United States with similar conidium morphology to that of P. eriochloae suggests that it may not be restricted to Australia.