Susceptibility of six Scots pine clones to the pathogenic fungus Gremmeniella abietina

Genotypic variation in susceptibility to Gremmeniella abietina, an economic ally important fungal pathogen of conifers, was studied by artificially ino culating 23-yr-old grafted plants of six Scots pine (Pinus sylvestris L.) c lones in a seed orchard. Two fungal isolates were used. The mycelium was in serted into the current year shoots in late winter and the length of the ne crotic Lesion caused by the fungus was measured the next spring. The growth and male flower production of the experimental shoots were also measured. The development of symptoms did not vary among the clones, but the location of the grafts within the orchard statistically significantly affected the length of necrosis. The clones differed significantly in regard to height a nd the production of male and female flowers. Differences in flowering inte nsity among the clones were not connected with the development of G. abieti na. At the level of the single shoot, the production of male flowers correl ated positively with the length of necrosis. The length of necrosis correla ted negatively with the length of current and previous year shoots. The abi lity of the two fungal isolates to cause necrosis differed significantly.