This is usually accompanied by an impaired ability to transport water to the leaves via
the outer xylem (the sapwood), courtesy of blue stain fungi (e.g. Grosmannia or Ceratocystis spp.) carried and introduced by the beetles.
Morphologically, the DZ in the wild type (WT) is marked by the appearance of epidermal root hairs on the external surface of
outer cell files (trichoblast) and the existence of fully differentiated
xylem for internal cell files (Dolan et al, 1993; Ishikawa & Evans, 1995; Beemster et al, 2003; Verbelen et al, 2006; Zhang et al, 2010; Mähönen et al, 2014).