Armillaria Luteobubalina - History and Phylogeny

History and Phylogeny

Armillaria luteobubalina was first described in 1978 by mycologists Roy Watling and Glen Kile, who studied its effects on a fast-growing plantation of Eucalyptus regnans near Traralgon, Victoria. The plantation, established in 1963, consisted largely of trees with a mean height of about 25 m (80 ft). A cluster of dead and dying trees discovered in 1973 suggested attack by a virulent primary pathogen, that is, one capable of infecting a host before invasion by other, secondary pathogens. This finding was inconsistent with the pathogenic behaviour of the known Armillaria species in Australia at the time, A. mellea and A. elegans. Further study over the next few years showed that the fungus spread by the growth of underground mycelia in root systems, expanding outward from the initial infected stump at an average of 2.5 m (8.2 ft) per year. Most Australian records of Armillaria infections referred to A. mellea, based on the presence of black rhizomorphs. For over one hundred years, A. mellea was thought to be a pleiomorphic (occurring in various distinct forms) species with a widespread distribution and host range, and variable pathogenicity. which led to great confusion among taxonomists and plant pathologists alike. In 1973, Veikko Hintikka reported a technique to distinguish between Armillaria species by growing them together as single spore isolates on petri dishes and observing changes in the morphology of the cultures. Using similar techniques, mycologists eventually determined that the Armillaria mellea species complex in Europe and North America in fact consisted of five and ten distinct "biological species", respectively.

Watling and Kile compared the macroscopic and microscopic characters of the pathogenic Armillaria with A. polymyces (now known as A. obscura), A. mellea, A. limonea and A. novae-zelandiae and found sufficient differences between them to warrant designating the species as new. Its specific epithet is derived from the Latin lutea "yellow", and was chosen to highlight an important distinguishing characteristic: the strong yellow colour of the cap and lack of reddish or brown tones in the stem typical of other resident Armillaria.

A phylogenetic study of South American Armillaria species concluded that A. luteobubalina is in a lineage that includes A. montagnei, and these are sister to a lineage containing A. paulensis, a species known from a single specimen collected in São Paulo, Brazil. Although they are very similar, specimens of A. luteobubalina have smaller spores than Argentinian specimens of A. montagnei, and their distinctness is well-supported with phylogenetic analysis. Based on analysis of pectic enzymes, A. luteobubalina is closely related to A. limonea, a species found in New Zealand; this result corroborates phylogenetic analyses reported in 2003 and 2006. Molecular analysis of 27 collections of A. luteobubalina from southwest Western Australia and one from Traralgon revealed four distinct polymorphic groups. The genetic variety suggests it is native to Australia.