Black Stain Root Disease in Ozone-Stressed Ponderosa Pine

Needle injury was greater and stem growth was less in seedlings inoculated with L. wageneri var. ponderosum than in noninoculated seedlings. The length of the black stain in roots of inoculated seedlings increased as the ozone exposure increased; 43% of the seedlings exposed to charcoal-filtered air (with an ozone concentration of 0.26 ppm-hr/day) had visible black staining, whereas 79% of those exposed to ozone at 2.84 ppm-hr/day were stained