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 (ΨP) 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 ΨP, 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
Highlights
Species of the genus Hevea, H. brasiliensis, are intensively cultivated and exploited in modern plantations for the latex
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 of rubber trees (Hevea spp.)
The first important thing is that HCNp of healthy rubber trees was low in the trunk bark compared to what is known in the literature for plants containing linamarin
Summary
Species of the genus Hevea, H. brasiliensis, are intensively cultivated and exploited in modern plantations for the latex. Rubber tree is an important industrial crop, natural rubber representing almost half (42% in 2005) of total world rubber production. The tapping panel dryness (TPD) is one of the most serious threats to natural rubber yield: it is estimated that TPD contributes to. 15–20% loss of the annual rubber production, with an incidence of 20–50% of productive trees affected by TPD, in almost every rubber‐growing regions. The TPD syndrome – first known as brown bast – is detected early by bark dryness upon tapping, i.e. partial or complete stoppage of latex flow on the tapping cut. The late macroscopic symptoms are brown spots in the barks, bark thickening, bark cracking and desquamations and, sometimes, bark deformations (Petch, 1921; de Faÿ, 1981; de Faÿ & Jacob, 1989b), which make the affected trees unsuited for latex production
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