Histo- and cytopathology of trunk phloem necrosis, a form of rubber tree (Hevea brasiliensis Müll. Arg.) tapping panel dryness

Abstract

Abstract. Trunk phloem necrosis (TPN) is a physiological disease of rubber tree (Hevea brasiliensis Müll. Arg.) discovered in the 1980s. It has been distinguished from rubber tree tapping panel dryness (TPD) by its macroscopic symptoms and presumed origin. But little attention has been paid to its microscopic features, and there is now some evidence that both syndromes could be linked to an impaired cyanide metabolism. In order to characterise TPN and compare it with TPD microscopically, the inner phloem of tapping panels was investigated by light and transmission electron microscopy in healthy trees and TPN-affected trees. TPN-affected phloem presented numerous and varied structural and ultrastructural features. There were signs of cellular deterioration in a great number of specialised cells, i.e. laticifers and sieve tubes, and not very specialised cells, i.e. parenchyma cells and companion cells. There were also signs of cellular dedifferentiation in other parenchymatous cells, e.g. in tylosoids and hyperplasic cells. These cells were derived from parenchyma cells that ensheath laticifers in which the latex coagulated. Numerous structural features of TPN are common to TPD, notably tylosoids associated with in situ coagulated latex, which are also known to be early structural markers of TPD and cyanide-induced. It is therefore concluded that TPN is identical to or a variant of TPD, and is a degenerative disease of rubber tree trunk phloem resembling plant stress response, programmed cell death and plant tumourigenesis in some aspects.

Transcriptome analyses reveal molecular mechanism underlying tapping panel dryness of rubber tree (Hevea brasiliensis)

“…Some researchers have suggested that PCD might occur in TPD rubber trees 9 10 11 12 14 . The typical characteristics of PCD, such as DNA laddering, chromatin condensation, and nuclear membrane blebbing, etc., were have been detected in TPD rubber trees 11 .…”

“…In laticifer cells, excessive oxidative stress can destabilize cellular membranes and trigger the lutoid burst with consequent latex coagulation in situ 6 . By investigating the histopathology and cytopathology of trunk phloem necrosis, de Faÿ concluded that trunk phloem necrosis is identical to or a variant of TPD and that it is a degenerative disease of the rubber tree trunk phloem somewhat resembling the plant stress response, programmed cell death (PCD), and plant tumourigenesis 9 .…”

Curative Activity of Watery Fermented Compost Extract as a Bark Treatment against Tapping Panel Dryness

“…In all trials, bark treatments on total-TPD trees resulted in poor disease recovery compared to those on partial-TPD trees, indicating that the treatment was less effective when applied during advanced stages of TPD when histological deformation of the bark occurred due to thylakoid formation, lignified gum, and abnormal division of parenchyma cells, ultimately causing irreversible total latex dryness [9]. The tapping cut of some treated trees started to secrete latex, but the latex was immediately coagulated (high plugging index), leading to low yield due to the short duration of flow during tapping.…”

“…This type of TPD is reversible after a resting period for the trees [8]. In the advanced stage, an irreversible type of total dryness, called bark necrosis [9] or brown bast TPD (BB-TPD), can occur [3]. The latter, which is related to a cyanogenesis process [7,10], involves histological deformation of the bark including browning, thickening, or even flaking due to thylosoid formation, lignified gum, and abnormal division of parenchyma cells [3,9].…”

Transcriptome analysis in Hevea brasiliensis latex revealed changes in hormone signalling pathways during ethephon stimulation and consequent Tapping Panel Dryness

“…Under exacerbated conditions, an irreversible type of TPD, called brown bast (BB), occurs. This form is related to deformation of the bark due to thylosoid formation, lignified gum, and abnormal division of parenchyma cells, and may be related to a cyanogenesis process 4 , 5 . These two types of TPD were recently called ROS-TPD and BB-TPD 6 .…”