ABSTRACT
Armillaria sp. is the pathogen causing root rot and death to Pinus trees in the south region of Brazil. Little is known about the morphophysiological and pathogenic aspects of this species. This study aimed to characterize the morphology, physiology, pathogenicity and in vitro basidiome production of Armillaria isolates from the south region of Brazil. Analysis of the mycelium and rhizomorph morphology was done with colonies grown on PDA medium (potato-dextrose-agar) at 20 °C, in the dark, for 30 days, and mycelial fan fragments produced in trunk sections inoculated with the fungus, using light and scanning microscopy. Physiology was based on the analysis of biomass produced in PD broth (potato-dextrose) at six temperatures. Pathogenicity test was done with Pinus taeda seedlings. Basidiome induction was done with P. taeda trunk sections inoculated in flasks containing PDA medium. Colonies presented variation in mycelial morphology, irregular growth without radial symmetry, coloration varying from white, to gray and to brown, and most often with rhizomorphs. Analysis of hyphae revealed typical structures of the Armillaria genus, such as clamp connections, septa, pilosities and resinous masses on the hyphal surface. Rhizomorph morphology appeared variable depending on the environment, presenting pilosities when developed in aerial growth and smooth surface when developed in the culture medium. The mycelial fan was crusted and had verrucous hyphae. Optimum temperatures for Armillaria isolates varied from 16 to 24 ºC. Only one inoculated plant died, indicating difficulty in reproducing the disease in vivo. One basidiome was produced, demonstrating the possibility of in vitro fruiting of Armillaria sp.
Keywords
basidiomycete; pathogenic fungus; Pinus
