Exclusion of Heterobasidion parviporum from inoculated clones of Picea abies and evidence of systemic induced resistance

Four groups of 30 4-year-old clones of Picea abies (L.) Karst. were inoculated with Heterobasidion parviporum (Fr.) Niemela & Korhonen. Trees were harvested at weeks 5, 14 and 34. Infection success was 95% and 61% at 5 and 14 weeks, respectively. At 34 weeks, the pathogen was completely excluded from all plants, An experiment to test for induced resistance was also conducted at 78 weeks. Seven ramets; per clone were reinoculated, using seven untouched ramets; of the same clones as the control. Fungal growth in sapwood and lesion length in inner bark differed significantly among clones. Previously inoculated plants showed significantly shorter fungal growth than untreated plants (p < 0.012). In conclusion, pretreatment with H. parviporum induces a systemic resistance response that lasts for at least 78 weeks.