Beech leaf disease (BLD), Litylenchus crenatae and its potential microbial virulence factors

American beech trees are critical sources of food and shelter for wildlife in northeastern U.S. forests. Beech leaf disease is an emerging forest disease first discovered near Lake Erie by Cleveland Metroparks biologists in 2012. Plant scientists from the U.S. and Canada demonstrated through the use of Koch’s postulates that symptoms could be transmitted in the greenhouse by nematodes new to North America, providing a focus for further research. This rapidly advancing disease recently reached the Atlantic coast up through Maine and down to West Virginia. This chapter documents high resolution fluorescent and low-temperature scanning electron microscopic images of diseased leaves that show reduced chlorophyll in infested leaves, damage and distortion of internal and external leaf tissue, and describes mites entwined with nematodes that could possibly transmit the disease. Various images of symptomatic leaves and a discussion of possible microbial co-factors that may relate to increased virulence in North America are included.