GENETICS OF CRONARTIUM-RIBICOLA .1. AXENIC CULTURE OF HAPLOID CLONES

Genetically pure lines of the mononucleate (haploid) stage of Cronarti um ribicola can be grown by isolating mycelium from single spots on in fected white pine needles or by culturing single basidiospores on defi ned media preconditioned by cell-free diffusates of massed germinating basidiospores. Although growth is initially slow, cultures can be inc reased rapidly by alternately subculturing from solid to liquid media and back again indefinitely. The ability to culture pure haploid clone s has important implications for studying the genetic structure and se xual behavior of rust populations and the nature of virulence.