Cyanogenesis and the onset of tapping panel dryness in rubber tree

Abstract

-The objective of this work was to study the influence of cyanogenesis on the onset of irreversible tapping panel dryness (TPD) and the physiological and histological aspects of secondary phloem in the trunk (tapping panel) of rubber trees (Hevea spp.). Two cyanogenic compounds, linamarin and KCN, were applied separately on the trunk bark of healthy mature trees belonging to two Brazilian clones (Fx 4098 and Fx 3899). Changes in histology, latex pressure potential (Ψ P ) and cyanogenic potential (HCNp) were followed in the trunk inner barks. In addition, the HCNp levels were determined in TPD-affected plants of both clones. The applications of linamarin or KCN in healthy plants decreased latex Ψ P , and formed tylosoids associated with in situ coagulation of latex. The clone Fx 4098 had the higher HCNp and showed the quicker and stronger responses to the cyanogenic compounds. Plants with TPD syntoms had a higher HCNp than the untreated healthy ones. Since histological changes are also structural markers of early TPD, it can be inferred that excessive release of cyanide can induce it in sensitive rubber clones.Index terms: Hevea, clonal sensitivity, cyanogenic potential, latex pressure potential, linamarin, secondary phloem. Cianogênese e estabelecimento do secamento de painel de sangria em seringueiraResumo -O objetivo deste trabalho foi estudar a influência da cianogênese no estabelecimento do secamento do painel de sangria (TPD) e os aspectos fisiológicos e histológicos do floema secundário do tronco (painel de sangria) em seringueira (Hevea spp.

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

“…The amount and frequent location of this material out of the sieve plates in the TPN-affected trees suggest that the sieve tubes were strongly injured but not mechanically. Furthermore, the cytological signs of sieve element degradation and decompartmentation in the TPN-affected trees were consistent with the early disappearance of conducting sieve elements in TPD-sensitive rubber clones following cyanogenic treatments (de Faÿ et al 2010).…”

“…There is thus histological evidence of a similarity between TPN and irreversible TPD. The similarity is supported by other facts: the impaired cyanide metabolism in TPN-affected rubber trees , and the cyanide-induction of tylosoids associated with in situ coagulated latex (de Faÿ et al 2010).…”

“…In hevea, cyanogenesis was initially studied by Lieberei et al (1985), and Moraes et al (2002). As previously mentioned, de Faÿ et al (2010) demonstrated that it was possible to induce the tylosoids associated with in situ coagulated latex in rubber tree by cyanogenic treatments. Taken together the present and previous results imply that cyanide induces dedifferentiation of axial parenchyma cells and cell death of the adjacent laticifers, and also leads to proliferation of dedifferentiated cells (since tylosoids give rise to hyperplasic cells).…”

“…However, it was recently shown in Brazilian clones differently sensitive to TPD that the structural abnormalities specific to irreversible TPD, i.e. tylosoids (kinds of tyloses formed in laticifers) associated with in situ coagulated latex de Faÿ 1981;de Faÿ and Jacob 1989), are cyanide-induced (de Faÿ et al 2010). TPD and TPN might thus have the same immediate cause.…”

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

“…TPD is detected early by bark dryness upon tapping, which can manifest as partial dry zones (no latex flow) [6]. Ultimately, the disease causes a complete stoppage of latex flow on the tapping cut [7]. The early onset of the syndrome is tapping cut dryness, which lacks any visible sign of bark necrosis and is related to overproduction of reactive oxygen species (ROS) in laticifers [3].…”