تقنية لشاشة الزان الأمريكية لمقاومة الحشرات والزان مقياس (<em> المستخفية fagisuga</em> ليند.)

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 disease weakens the tree, making it prone to snapping in high winds⁴. Mortality levels in the first wave of the disease have been reported to be as high as 50%⁵. Surviving trees are often severely deformed as cankers form reducing value of the tree as a wood product. Such trees have a propensity for root-sprouting which leads to the formation of “beech thickets” that prevent other more desirable species from establishing, reducing the economic and ecological value of the stand⁶. Although beech bark disease is not likely to lead to extinction of the American beech, it alters stand composition and health leading to a decrease in food and habitat for wildlife^7,8.

In stands affected by BBD for many years, trees that remain free of any symptoms of the disease have been reported. Artificial inoculation trials have shown that these trees are resistant to the scale insect². Without scale infestation, there is little opportunity for Neonectria infection, minimizing the impact of the fungus. Large scale mortality in American beech due to Neonectria infection in the absence of prior scale infestation has never been reported, so resistance to the beech scale insect results in resistance to BBD. 

Recent research on management of BBD has focused on the identification, propagation, breeding, and retention of American beech trees with resistance to the beech scale insect. Genetic studies have shown that resistance to the scale insect is heritable and careful selection and breeding of resistant trees can result in significant improvement in a single generation⁹. This finding has fueled efforts by state and national forest managers in the United States to establish regional seed orchards of resistant American beech to provide a source of genetically diverse BBD-resistant seed for restoration plantings^10,11. Research has also indicated that silvicultural manipulation of stand genetics by the removal of susceptible trees and retention of resistant trees can result in stand improvement^9,12. 

Management of BBD through tree improvement activities or through carrying out silvicultural prescriptions requires the ability to select for and distinguish between beech scale-resistant and susceptible trees. The methods presented here have been adapted from a method first introduced by Dave Houston to artificially inoculate seedlings with beech scale eggs¹. The method can be used as a screening tool to identify quantitative trait loci (QTL) associated with resistance or to distinguish between resistant and susceptible potted seedlings or grafted ramets in genetic studies. Alternatively, it can be used for screening mature trees in the field to identify resistant trees for seed orchard development, or retention in the field. Susceptible trees can be identified and removed to minimize disease impacts. 

Protocol

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

Representative 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

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
			http://www.amazonsupply.com/dp/B000FMWH1S/ref=sp_dp_g2c_asin
Tyvek Home Wrap	DuPont	D1349991	9 ft x 150 ft roll, can ask for it to be cut in half.
			http://www.lowes.com/pd_14582-2020-D13499991_0__
Polyethylene foam, ½” thick	Columbus Foam Products	N/A	2 ft x 50 ft roll
			http://www.colsfoam.com/apcfp/products.htm
MetroMix 510	Sun Gro	N/A	2.8 cu. ft. bark, peat moss, vermiculite, bark ash, starter nutrient charge (with Gypsum), slow release nitrogen and dolomitic limestone.
	Horticulture		http://sungro.com/products_displayProduct.php?product_id=118&brand_id=17
Osmocote Plus 15-9-12	Everris	E903206	Standard 3-4 month release.
			http://everris.us.com/product/15-9-12
Sight Savers 10 X	Bausch & Lomb	813434	10 x magnification illuminated coddington
			http://www.amleo.com/Bausch—Lomb-Illuminating-Codington-Magnifier-10x/p/CM10/
Nikon Mini Field Stereoscope	Nikon	7314	20 x magnification
			http://www.opticsplanet.com/nikon-fieldmicroscope.html
Silicone II clear	GE	159538	2.9 oz clear window & door caulk
			http://www.midlandhardware.com/159538.html