VIEW ARTICLE

Stimulation of Rhizomorph Production by Armillaria mellea with Lipid from Tree Roots. A. R. Moody, Assistant Research Plant Pathologist, Department of Plant Pathology, University of California, Berkeley 94720, Present address: Station Federale de Recherches Agronomique de Lausanne, Chateau de Changrins, CH–1260 Nyon, Switzerland; A. R. Weinhold, Professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 62:1347-1350. Accepted for publication 30 May 1972. DOI: 10.1094/Phyto-62-1347.

Lipid extracts from roots of ponderosa pine (Pinus ponderosa), Douglas fir (Pseudotsuga menziesii), white fir (Abies concolor), incense cedar (Calocedrus decurrens), and peach (Prunus persicae) stimulated rhizomorph production in Armillaria mellea. Unsaponifiable lipid from roots of ponderosa pine was inactive, whereas saponifiable lipid was active. Further separation indicated activity due to unsaturated fatty acids and possibly to resin acids. To stimulate rhizomorph production a minimum concentration of 0.05 to 0.1% active fatty acid is required. The amount of unsaturated fatty acid in fresh roots of ponderosa pine (0.23%) is sufficient to stimulate rhizomorph production, whereas the quantity in peach (0.03%) is marginal. Insufficient amounts were found in Douglas fir (0.01%), white fir (0.006%), and incense cedar (0.005%). The quantity of active fatty acid in the roots of these trees correlates with susceptibility to Armillaria root rot. Althought this probably does not govern resistance, it may be important when considering roots as a food source for the fungus after infection. The resin acid fraction and hot water extracts of root tissue also contributed to rhizomorph production, indicating that these materials may also play a role in stimulating growth and rhizomorph production by A. mellea during colonization of roots.