Cryptic diversity found in Didymellaceae from Australian native legumes

Area of Science:

• Mycology and Plant Pathology
• Fungal Taxonomy and Phylogenetics
• Australian Flora and Fauna

Background:

• Ascochyta koolunga, identified as a pathogen of field pea (Pisum sativum) in South Australia, has not been reported globally since its 2009 description.
• The origin and potential hosts of A. koolunga among Australian native, pasture, and naturalized legumes remain uninvestigated.

Purpose of the Study:

• To investigate the potential native origin of Ascochyta koolunga by surveying blight and leaf spot diseases on Australian legumes.
• To discover and classify novel fungal species within the Didymellaceae family associated with Australian native legumes.

Main Methods:

• Field surveys were conducted across southern Australia to collect leaf spot and blight samples from various legume species.
• Fungal isolates were identified using morphological characteristics and phylogenetic analyses of the internal transcribed spacer (ITS) and RNA polymerase II subunit B (RPB2) gene regions.
• New species were formally described based on these analyses.

Main Results:

• Ascochyta koolunga was not detected on any surveyed native, naturalized, or pasture legumes exhibiting leaf spot symptoms; only one isolate was recovered from Pisum sativum.
• Five novel species within the Didymellaceae family were isolated from leaf spots of Australian native legumes: Nothophoma garlbiwalawarda sp. nov., Nothophoma naiawu sp. nov., and Nothophoma ngayawang sp. nov. (from Senna artemisioides); Epicoccum djirangnandiri sp. nov. (from Swainsona galegifolia); and Neodidymelliopsis tinkyukuku sp. nov. (from Hardenbergia violacea).
• New host-pathogen associations were reported for Didymella pinodes (on S. artemisioides and Vicia cracca), D. lethalis (on Lathyrus tingitanus), and the first Australian record of Didymella prosopidis.

Conclusions:

• Ascochyta koolunga does not appear to originate from or commonly infect native Australian legumes.
• The study significantly expands the known fungal diversity within the Didymellaceae family in Australia, with the discovery of five new species.
• This research highlights the importance of studying fungal pathogens on native flora to understand biodiversity and potential host-pathogen interactions.