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

Summary

Beech bark disease is initiated by feeding activities of the beech scale insect that create fungal entry points in the bark. Trees that are resistant to the scale insect are also disease resistant. Here we present the protocol we have developed to screen individual beech trees for beech scale resistance.

Abstract

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 complex¹. Here we present a protocol that we have developed, based on the artificial infestation technique by Houston², 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.

Introduction

Beech bark disease (BBD) has had a detrimental impact on American beech in North America since the introduction of the invasive beech scale insect, Cryptococcus fagisuga, in the Canadian province of Nova Scotia in the late 1890s³. This insect-disease complex is initiated when the beech scale insect inserts its feeding stylet into the bark creating small fissures that provide entryway for infection by one of the Neonectria species of fungus (Neonectria ditissima or Neonectria faginata). As the fungal mycelia grow, large areas of tissue may die, eventually completely girdling the tree. The damage from the dis....

Protocol

1. Plant Material: Mature Field Trees, Potted Seedlings, or Potted Grafts

1. For field testing, select mature healthy American beech trees that show no signs of scale infestation or disease for testing for possible resistance. Visibly susceptible trees will also need to be identified to be used as a control (Figure 1).
2. For testing potted seedlings or grafts, collect and germinate beechnuts as described in Koch & Carey, 2004 or graft scion as described in Carey et al, 2013.
3. Grow seedlings or grafts in potting soil mix amended with 47 g micronutrients, 477 g slow release fertilizer 15N-3.9P-9.9K, 700 g coarse pe....

Results

Figure 6 shows a resistant seedling (C) and two susceptible seedlings (D, E) exhibiting different degrees of susceptibility. An example of what a susceptible mature tree looks like 57 weeks after the artificial infestation test was set up is shown in Figure 5B. When the foam is peeled away from the tree, it is not uncommon for scale insects and their egg clusters to remain stuck to the foam as shown in Figure 7, which is.......

Discussion

The critical steps required for success of this assay include performing a viability test on the eggs and the use of susceptible controls at each site tested, and with potted materials. It is also important to use more than one test pad per tree or seedling. We have found that both in the field and in more controlled tests on potted plants, a frequent source of error can be pad failure. For example, in the field, even with our modification of covering the test pad with house wrap to prevent excess moisture.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Nylon Mesh Sheet, 250 micron	Small Parts	CMN-0250-D	Mesh opening size: 250 microns square, % of open area: 34, thread diameter: 180 micron, width: 24”, Length: 12”, Package quantity: 1
Tyvek Home Wrap	DuPont	D1349991	9 ft x 150 ft roll, can ask for it to be cut in half.
Polyethylene foam, ½” thick	Columbus Foam Products		2 ft x 50 ft roll
MetroMix 510	Sun Gro Horticulture		2.8 cu. ft. bark, peat moss, vermiculite, bark ash, starter nutrient charge (with Gypsum), slow release nitrogen and dolomitic limestone.
Osmocote Plus 15-9-12	Everris	E903206	Standard 3-4 month release
Sight Savers 10X	Bausch & Lomb	813434	10X magnification illuminated coddington
Nikon Mini Field Stereoscope	Nikon	7314	20X magnification
Silicone II clear	GE	159538	2.9 oz clear window & door caulk