Abstract
Scotch pine seedlings from 5 seed sources were inoculated with S. acicola 5 days before or 30 min after fumigation for 6 h with 533 .mu.g/m3 (0.20 ppm) of SO2, 399 .mu.g/m3 (0.20 ppm) of ozone, or the same levels of ozone and SO2 combined. After 8 wk, seedlings inoculated 5 days before fumigation had more lesions incited by S. acicola than those inoculated 30 min after fumigation. Ozone caused more needle injury than SO2 did. The amount of injury caused by the combined gases was a greater-than-additive effect. The degree of infection varied significantly among the seed sources.