Studying graft incompatibility between Hevea species,
Moraes et al. (2002) budded crown clones resistant
to Microcyclus ulei (P. Henn). v. Arx, the causative agent
of South American leaf blight (SALB), on productive
panels. The authors established connections between the
translocation of cyanogenic glycosides from the budded
crown to the panel and the development of symptoms
similar to tapping panel dryness (TPD), a physiological
disorder whose immediate cause remains unknown. TPD
syndrome affects latex biosynthesis and causes great loss
to rubber producers worldwide (Venkatachalam et al.
2009). According to Moraes et al. (2002), the symptoms
that they observed started with destabilization of latex
and developed to its coagulation in laticifers and trunk
bark necrosis. The damage by releasing toxic HCN in
tissue of stem during tapping, such as cell death and
tissue necrosis, could also facilitate the establishment of
pathogens. Recently, a low-molecular-weight RNA
(LMW RNA) similar to viroid RNA was isolated from
TPD-affected samples of rubber tree. The LMW RNA
isolated from TPD-affected trees was found to cause
infections on seedling of tomato cv. Pusa Ruby