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

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.