A TAXONOMIC REASSESSMENT OF PHYLLACHORA PROTEAE, A LEAF PATHOGEN OF PROTEACEAE
S DENMAN1, PW CROUS1 and MJ WINGFIELD2
1Department of Plant Pathology, University of Stellenbosch 7600, Stellenbosch, South Africa; 2FABI, University of Pretoria, Pretoria 0002, South Africa
Background and objectives
The plant family Proteaceae is one of the main components of the South African Fynbos biome, which is represented by at least 1400 species. The unique beauty and hardiness of Protea flowers make them highly desirable for the cut-flower industry, both in local and international markets. Strict phytosanitary regulations, however, frequently prevent blemished blooms from reaching potential export markets. The correct identification of fungal pathogens is therefore necessary to ensure that their relevance is appropriately applied in quarantine decisions. Phyllachora proteae, commonly associated with leaf spots and stem cankers of Protea, Leucadendron and Leucospermum, is an example of a pathogen that requires reassessment. This fungus was described by Wakefield  as having unilocular ascomata that developed under a very small epidermal clypeus, cylindrical asci, pseudoparaphyses and hyaline, aseptate, ellipsoidal ascospores, 19-22x8-9 µm. The aims of this study were to re-collect isolates of P. proteae, compare them with the type specimen, identify its anamorph(s), and to record new hosts and collection sites.
Materials and methods
Necrotic leaves and stem cankers were collected from Protea aristata cv. Venus, P. cynaroides, P. eximia , P. grandiceps, P. magnifica and P. repens and from a few Leucadendron and Leucospermum spp. from various farms in the Western Cape province. Diseased material, including a sample from Maui, Hawaii, was examined. Leaf and stem pieces bearing pseudothecia were soaked in water for 1-2 h, then fixed to the lids of Petri dishes containing potato dextrose agar (PDA). After 24 h individual germinating ascospores were transferred onto fresh PDA plates. Hyphae of developing colonies were transferred to divided plates containing water agar with a sterile irradiated carnation leaf in one half of the dish and PDA in the other. Isolations were incubated at 20°C under near-ultraviolet light with a 12 h photoperiod.
Results and conclusions
Host range and distribution: the known host range of P. proteae has been extended, and new records of its occurrence on Protea aristata, P. cynaroides, P. eximia and P. grandiceps are made here. The extensive area from which it was collected suggests that it occurs commonly on the Proteaceae in the Western Cape province of South Africa. A single collection from a Protea sp. in Hawaii, suggests that it also occurs in other areas of the world where Proteaceae are cultivated.
Identification: after 4-8 weeks a coelomycete anamorph with two synanamorphs was derived from single ascospore cultures. One anamorph was a typical species of Fusicoccum, while the other was Sphaeropsis-like. The Fusicoccum state was characterised by having one-celled, hyaline, navicular conidia (21-)23-25(-30) x (3-)4-5(-5.5) µm. The Sphaeropsis state had smaller conidia (7-)9-9.5(-14) µm, which were brown, subcylindrical with obtuse apices and truncate bases. Pseudothecia of the teleomorph had thick walls consisting of brown pseudoparenchymatic cells. Asci were bitunicate, cylindrical, briefly stipitate and intermingled with numerous pseudoparaphyses that extended above the asci. Ascospores were hyaline, aseptate, ovoid to ellipsoid with the widest part of the cell above the median point, measuring (15-)17-18(-19) x (6-)6.5-7(-8.5) µm. The characteristics of the teleomorph corresponded well with those of the type specimen of Phyllachora proteae. The bitunicate asci clearly exclude this fungus from Phyllachora. The morphology of both the teleomorph and anamorph states of this fungus suggest that it would be better accommodated in Botryosphaeria than Phyllachora.
1. Wakefield EM, 1922. Fungi Exotica XXVI, Kew Bulletin.