We tested whether the pairing of selected isolates could be used to increase the efficiency of a decay fungus Chondrostereum purpureum (Pers. Ex Fr.) Pouzar to control hardwood sprouting in Finland. We paired C. purpureum strains efficient in sprout control or highly active in laccase production, and tested the efficacy of their progeny in spout control experiments. This procedure resulted in a strain with an efficacy superior to that of the parental strains. The mortality of birch (Betula pendula Roth. and B. pubescens Ehrh.) 1 cm in stump diameter was 78%, 56% and 9% for the best progeny, the best parental strain and the control, respectively. Mortality was only slightly higher for B. pendula than for B. pubescens but no significant differences were found between the number or maximum height of stump sprouts. Our results showed that cross breeding of this decay fungus is a good alternative in attempts to produce efficient biocontrol agents against hardwood sprouting.

No abstract

To test the effect of application time on the efficacy of a biological control agent to prevent sprouting of cut stumps, birches ( Betula pendula Roth. and Betula pubescens Ehrh.) were cut and stumps treated with a decay fungus ( Chondrostereum purpureum (Pers. ex Fr.) Pouzar) at different times during one growing season. Applications were conducted at 2 week intervals. The presence of fruiting bodies was examined three times during the 2 years following treatment. Sprouting was measured twice. Fructification was most abundant 1 year after the treatment, and the frequency of stumps with fruiting bodies was highest when the stumps were treated between May and July. Treatment reduced the percentage of living stumps compared with controls, except if conducted in late autumn. The reduction was the highest on stumps treated in the middle of July; 2 years after the treatment, only 12.5% of treated stumps were resprouting compared with 74% of control stumps. Also, the number of living sprouts per stump decreased by the treatment, except if conducted in late autumn. Although the number of living sprouts per stump decreased owing to C. purpureum treatment, it had no effect on the maximum height of the sprouts.

We analysed genetic variation in the natural populations of a potential herbicide biocontrol agent, Chondrostereum purpureum, in Nordic and Baltic countries using random amplified microsatellite markers. The results showed high genetic diversity among the populations of this fungus, but almost a complete lack of local differentiation. The results implicate that any local strain from the area can be used as a biocontrol agent without a fear of introducing new genotypes to treatment areas.

We artificially inoculated pruning wounds of silver birch (Betula pendula Roth) to study seasonal variation in their vulnerability to infection by the fungal decomposer Chondrostereum purpureum (Pers. ex Fr.) Pouzar. This information is critical to the assessment of incidental infection risks in areas where C. purpureum may be used as a bioherbicide. On seven monthly occasions between April and October 2005, 30 birch trees were pruned to yield a total of 210 experimental trees. On each occasion, 10 trees were inoculated immediately with C. purpureum mycelium, 10 were inoculated with blank inoculum and 10 were only pruned. In the summer of 2007, a survey of 129 experimental trees showed that pruning wounds were most susceptible to infection during May. Treatment with C. purpureum at other times during the growing season also increased the extent of discoloration or decay but the effect was considerably less.