David W. Carey

Assessment of beech scale resistance in full- and half-sibling American beech families

A beech bark disease infested American beech tree (Fagus grandifolia Ehrh.) and two uninfested trees were selected in a mature natural stand in Michigan, USA, and mated to form two full-sib families for evaluating the inheritance of resistance to beech scale (Cryptococcus fagisuga Lind.), the insect element of beech bark disease. Four half-sib families from both infested and uninfested trees were also evaluated for resistance. Using an artificial infestation technique, adult and egg count data were collected over 2 years and analyzed with generalized linear mixed methods to account for nonnormal distributions of the response variables. A significant effect for family was found for each variable. Family least squares means were computed as a measure of resistance and repeatabilities were calculated to provide an upper limit estimate of broad-sense heritability. The two families that ranked highest for resistance were the full-sib family from two uninfested parents and the half-sib family from a stand where all diseased trees had been removed. Together, the results suggest that selection and breeding may be an effective means to improve populations for artificial regeneration, and silvicultural treatments may provide an effective management option for mitigating beech bark disease through managing the genetic composition of natural regeneration.

Intraspecific variation in Fraxinus pennsylvanica responses to emerald ash borer (Agrilus planipennis)

The emerald ash borer (EAB; Agrilus planipennis Fairmaire) is a bark and wood boring beetle native to east Asia that was first discovered in North America in 2002. Since then, entire stands of highly susceptible green ash (Fraxinus pennsylvanica Marshall) have been killed within a few years of infestation. We have identified a small number of mature green ash trees which have been attacked by EAB, yet survived the peak EAB infestation that resulted in mortality of the rest of the ash cohort. Adult landing and feeding preference bioassays, leaf volatile quantification and EAB egg bioassay experiments were used to characterize potential differences in responses of these select “lingering” green ash trees relative to known EAB susceptible controls. Three selections were identified as being significantly less preferred for adult feeding, but no specific leaf volatile profile was associated with this reduced preference. Egg bioassays identified two ash selections that had significant differences in larval survival and development; one having a higher number of larvae killed by apparent host tree defenses and the other having lower larval weight. Correlation and validation of the bioassay results in replicated plantings to assess EAB resistance in the field is still necessary. However, the differences between lingering ash selections and susceptible controls measured by these bioassays indicate that more than one mechanism is responsible for the increased resistance to EAB that resulted in these selections surviving longer than their counterparts. Efforts to further increase ash resistance to EAB through use of these selections in a breeding program are underway.

A Technique to Screen American Beech for Resistance to the Beech Scale Insect (Cryptococcus fagisuga Lind.)

Beech bark disease (BBD) results in high levels of initial mortality, leaving behind survivor trees that are greatly weakened and deformed. The disease is initiated by feeding activities of the invasive beech scale insect, Cryptococcus fagisuga, which creates entry points for infection by one of the Neonectria species of fungus. Without scale infestation, there is little opportunity for fungal infection. Using scale eggs to artificially infest healthy trees in heavily BBD impacted stands demonstrated that these trees were resistant to the scale insect portion of the disease complex(1). Here we present a protocol that we have developed, based on the artificial infestation technique by Houston(2), which can be used to screen for scale-resistant trees in the field and in smaller potted seedlings and grafts. The identification of scale-resistant trees is an important component of management of BBD through tree improvement programs and silvicultural manipulation.

Use of microsatellite markers in an American beech (Fagus grandifolia) population and paternity testing

Abstract Cross-species amplification of six microsatellite markers from European beech (Fagus sylvatica Linn) and nine markers from Japanese beech (Fagus crenata Blume) was tested in American beech (Fagus grandifolia Ehrh.). Three microsatellites from each species were successfully adapted for use in American beech and were found to be highly polymorphic, with 4-22 alleles at each locus and an expected heterozygosity value of 0.291 to 0.913. Twenty-five trees (including two clonal clusters) from a mature stand were sampled and genotyped to compute population statistics. No linkage disequilibrium between pairs of loci was detected, and the marker loci indicated that the population is at Hardy- Weinberg equilibrium. The markers were also used to genotype two full-sibling families consisting of a combined total of 99 individuals and were found to contain sufficient genetic information to assign paternity using a maximum likelihood method.