Highlights: Genetic variation is demonstrated in response to artificial inoculations with Heterobasidion parviporum and Ceratocystis polonica both between parents and their offspring;Strong relationships are observed between the male parents and their off-spring, less so between the female parents and their offspring.
Inoculations with the two fungi Heterobasidion parviporum and Ceratocystis polonica were made in two series of progeny tests each containing full-sib families planted at two sites and on grafts of the parents in two seed orchards. Significant variation among families in lesion lengths after inoculation was found for both fungi and a predominantly additive inheritance was indicated. The estimates of narrow sense heritability were 0.13 and 0.22 for H. parviporum and C. polonica, respectively. The estimate of the genetic correlation between the lesion lengths of the two fungi was as low as 0.12. Significant variation in lesion lengths was also found among parental clones, and within ramets of the same clone, in the seed orchards. In one of the series a high positive correlation (r = 0.88) was found between the H. parviporum lesion lengths of the male parents and offspring, but not for the female parents and off-spring. The results confirm earlier conclusions that the genetic variation and heritabilities are large enough for practical breeding for resistance.