New developments in chemical control of white root disease of Hevea brasiliensis in Africa

International audienc

Natural rubber systems and climate change: Proceedings and extended abstracts from the online workshop, 23–25 June 2020

The International Rubber Study Group (IRSG), with the International Rubber Research and Development Board (IRRDB), the CGIAR research program on Forests, Trees and Agroforestry (FTA) led by CIFOR, and the French Agricultural Research Centre for International Development (CIRAD), ran an open digital workshop on natural rubber systems and climate change on 23–25 June 2020, attended by more than 500 scientists and stakeholders. The purpose of the workshop was to review recent research results on impacts of climate change on rubber production, potential means of adaptation and contribution to mitigation of climate change, and to identify knowledge and research gaps as well as recommendation for action. This document brings together the extended abstracts of the presentations and summaries of the discussions held during the workshop

Is growth performance in rubber (Hevea brasiliensis) clones related to xylem hydraulic efficiency?

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Carbohydrate reserves as a competing sink: evidence from tapping rubber trees

Carbohydrate reserve storage in trees is usually considered a passive function, essentially buffering temporary discrepancies between carbon availability and demand in the annual cycle. Recently, however, the concept has emerged that storage might be a process that competes with other active sinks for assimilate. We tested the validity of this concept in Hevea brasiliensis Mull. Arg. (rubber) trees, a species in which carbon availability can be manipulated by tapping, which induces latex regeneration, a high carbon-cost activity. The annual dynamics of carbohydrate reserves were followed during three situations of decreasing carbon availability: control (no tapping), tapped and tapped with Ethephon stimulation. In untapped control trees, starch and sucrose were the main carbohydrate compounds. Total nonstructural carbohydrates (TNC), particularly starch, were depleted following bud break and re-foliation, resulting in an acropetal gradient of decreasing starch concentration in the stem wood. During the vegetative season, TNC concentration increased. At the end of the vegetative season, there were almost no differences in TNC concentration along the trunk. In tapped trees, the vertical gradient of starch concentration was locally disturbed by the presence of the tapping cut. However, the main effect of tapping was a dramatic increase in TNC concentration, particularly starch, throughout the trunk and in the root. The difference in TNC concentration between tapped and untapped trees was highest when latex production was highest (October); the difference was noticeable even in areas of the trees that are unlikely to be directly involved in latex regeneration, and it was enhanced by Ethephon stimulation, which is known to increase latex metabolism and flow duration. Thus, contrary to what could be expected if reserves serve as a passive buffer, a decrease in carbohydrate availability resulted in a net increase in carbohydrate reserves at the trunk scale. Such behavior supports the view that trees tend to adjust the amount of carbohydrate reserves stored to the level of metabolic demand, at the possible expense of growth