Ascochyta koolunga (Didymellaceae, Pleosporales) was first described in 2009 (as Phoma koolunga) and identified as the causal agent of Ascochyta blight of Pisum sativum (field pea) in South Australia. Since then A. koolunga has not been reported anywhere else in the world, and its origins and occurrence on other legume (Fabaceae) species remains unknown. Blight and leaf spot diseases of Australian native, pasture and naturalised legumes were studied to investigate a possible native origin of A. koolunga. Ascochyta koolunga was not detected on native, naturalised or pasture legumes that had leaf spot symptoms, in any of the studied regions in southern Australia, and only one isolate was recovered from P. sativum. However, we isolated five novel species in the Didymellaceae from leaf spots of Australian native legumes from commercial field pea regions throughout southern Australia. The novel species were classified on the basis of morphology and phylogenetic analyses of the internal transcribed spacer region and part of the RNA polymerase II subunit B gene region. Three of these species, Nothophoma garlbiwalawardasp. nov., Nothophoma naiawusp. nov. and Nothophoma ngayawangsp. nov., were isolated from Senna artemisioides. The other species described here are Epicoccum djirangnandirisp. nov. from Swainsona galegifolia and Neodidymelliopsis tinkyukukusp. nov. from Hardenbergia violacea. In addition, we report three new host-pathogen associations in Australia, namely Didymella pinodes on S. artemisioides and Vicia cracca, and D. lethalis on Lathyrus tingitanus. This is also the first report of Didymella prosopidis in Australia.

Phoma koolunga is one of three species that cause ascochyta blight (synonym: blackspot) of field pea (Pisum sativum L.) in Australia. P. koolunga was first described in 2009 in South Australia and has since been reported in Western Australia and Victoria. However, the origin of the pathogen and its host range remain largely unknown. The aim of this study was to examine the host range of P. koolunga and to explore possible origin(s) of P. koolunga as a pathogen of field pea in Australia. Host range experiments were conducted in a growth room using 41 legumes comprising Australian native, naturalised, crop and pasture legumes, and wild type Pisum, Lathyrus and Vicia spp. Two isolates of P. koolunga from field pea in South Australia were compared. Disease incidence and severity were measured as number of leaves and percentage of leaf area diseased every 4 days up to 12 days post-inoculation. All legumes tested, except Cicer arietinum (chickpea), developed leaf lesions and some also had stem lesions. Disease incidence and severity differed significantly among species but not consistently between the P. koolunga isolates. The ability of the isolates to cause lesions on a wide range of legumes in controlled environment conditions suggests the fungus has a broad host range in humid and mild temperature conditions conducive for disease development. These results provide no evidence to suggest P. koolunga could have evolved with any of the 17 Australian native legume species tested and the fungus is, therefore, unlikely to have originated within Australia.