Armillaria altimontana, a new species from the western interior of North America.

Armillaria altimontana, previously considered North American biological species (NABS) X, is described as new. To date, it appears that A. altimontana prefers higher-elevation, mesic sites within the dry, conifer forest zone of western interior North America. This species has been found on hardwoods and conifers and is associated most commonly with Abies-dominated forest types in southern British Columbia, Washington, Oregon, Idaho and northern California. Partial elongation factor 1-alpha (tef1) sequences were generated from six isolates of A. altimontana originating from three locations in northern Idaho. Phylogenetic analyses of all 10 North American Armillaria species were carried out with maximum parsimony and maximum likelihood. Results indicate that isolates of A. altimontana formed a monophyletic group and clustered with A. calvescens, A. cepistipes, A. gallica and A. nabsnona, which is in agreement with recent phylogenetic studies of Armillaria.

Taxonomy of Armillaria in the Patagonian forests of Argentina.

The taxonomy of Armillaria in southern South America has received little attention since the work of Singer and others. In this study we examine the morphological traits and cultural features for taxa representing the lineages revealed based on molecular phylogeny, and we link them to previously described taxa based on morphology. Lineages I-IV were identified as Armillaria novae-zelandiae, A. montagnei, A. umbrinobrunnea comb. nov. and A. sparrei respectively. They could be differentiated morphologically based on dimension, features of the epicutis, annulus, stipe, hymenophoral trama and flavor and characteristics in culture. Furthermore there was no evidence of host preference for the species recognized. This is the first study integrating the phylogeny and morphology of Armillaria species from Patagonia, and it provides a foundation for future research on these fungi in South America.

Biomechanics of invasive growth by Armillaria rhizomorphs.

Rhizomorphs of wood-decay basidiomycetes are root-like structures produced by the coordinated growth of thousands of hyphae. Very little is known about their development nor the way that they penetrate soils and rotting wood. In this study, we applied techniques used in previous studies on hyphae to explore the mechanics of the invasive growth process in Armillaria gallica. Growth rate measurements were made in media with different gel strengths. The osmolyte composition of rhizomorph sap was determined spectroscopically and the forces exerted by growing tips were measured using a force transducer. Cultured rhizomorphs extended at much faster rates than unbundled hyphae (3.5mmd(-1) versus 1.5mmd(-1)) and their growth accelerated in response to increased medium gel strength (to 7.4mmd(-1)). Measurements of rhizomorph osmolality provided a turgor pressure estimate of 760kPa (7.5atm.), and spectroscopic analysis showed that this pressure was generated by the accumulation of erythritol, mannitol, and KCl. Forces exerted by growing tips ranged from 1 to 6mN, corresponding to pressures of 40-300kPa (0.4-3.0atm.). Pressures exerted by extending rhizomorphs are comparable to those produced by individual vegetative hyphae. This suggests that the mechanical behavior of hyphae is similar whether they grow as unbundled cells or aggregate to form macroscopic rhizomorphs.