October Speaker Report: USQ Associate Professor John Dearnaley on the topic “Mycorrhizal Associations of Australian Plants”

 Fungi are referred to as the Fifth Kingdom and are more closely related to animals than plants even though many of them grow in soil. They have thread-like cells called “hyphae” which are composed not of cellulose but of chitin. It is estimated that worldwide there are more than 1 million species, about 100,000 of which have been described – many habitats have not been explored, and paid mycologists are rare.

The economic importance of fungi includes their value as high protein food, medicinal use, and as bio-controls. The downside is that they can cause disease, are poisonous in some cases, and can negatively affect our food. They are decomposers and recyclers. Fungal spores are invisible to the naked eye and can be found on every surface in our world.

The word mycorrhiza is derived from Greek words meaning “fungus root”. Symbiotic association between fungi and plants is present in about 80% of plants – fungal mycorrhiza live in or on plant roots, bringing with them nutrients such as water, phosphate, zinc and copper in return for sugar – some plants are highly depen-dent. Most mycorrhizal fungi don’t produce fruiting bodies, so are currently identified by the sequencing of their DNA and comparison to a large data base.

The four types of mycorrhizal association are:

·         Arbuscular mycorrhizas (AM) where mycorrhiza are found on the outside and inside of the plant roots. They are found in association with native plants such as ferns and allies, cycads, Araucaria spp., and Angiosperm families such as Asteraceae, Fabaceae, Mimosaceae, Rutaceae, Solanaceae and Poaceae. Fossilised remains dating back to 400 million years ago have been found – plants and fungi evolved side by side.

·         Ectomycorrhizal (ECM) association – the mycorrhiza form a sheath around plant cells rather than invading them. Examples include all Eucalypts, and species of Casuarina. Eucalypts are not fussy about their fungal partners, and may associate with fungi such as Amanita, Boletellus, Cortinarius, Russula, Pisolithus and others. Fruiting bodies of these fungi may be sometimes seen under trees or projecting from the trunks or roots.

·         Ericoid mycorrhizas (EM) form a loose mantle on plant roots, with coils inside the cells. Examples are plant families Ericaceae and Epacridaceae, heaths and heathers.

·         Orchid mycorrhizas (OM) form coils inside the plant cells. Orchidaceae is the largest plant family, and members are very specific and fussy about their fungal associations - the presence of a suitable fungus controls the distribution of the plant. In addition, the seeds of some orchids such as Dipodium spp. (hyacinth orchids) require certain fungi to germinate. Some orchids even have a three-way association with a Eucalypt and an ectomycorrhizal fungus, making the orchid parasitic on the Eucalypt! Orchids such as Gastrodia sesamoides and the Bootlace Orchid Erythrorchis cassythoides cannot produce their own food, but are dependent on wood-rotting fungi, Campanella spp. and Gymnopus spp. respectively. These are often seen on dead Eucalyptus trees.

Some plants don’t require the services of fungi to live and grow. These include Brassicas, saltbush, sundews, Banksias and Grevilleas. Appropriate mycorrhizal fungi added to agricultural crops can improve nutrient uptake, drought tolerance, and pathogen defence. They play important roles in both natural and agricultural/ horticultural systems. Our thanks to Associate Professor Dearnaley for his informative and interesting presentation, which included many more examples than have been listed here.

(Report by Glenda Walter)