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Brown Bast is the main phenomenon which limits production in Hevea brasiliensis plantations, lying ahead of fungal diseases affecting roots, leaves, or tapping panel tissue. The disease is in effect mainly associated with too intensive exploitation of trees, leading to physiological imbalance and the stopping of latex flow. This physiological imbalance, aggravated by tapping, may also follow poor ecological conditions. The effect of ecological conditions, climate, and soil on the onset of the disease are examined in turn. This mainly concerns experimental or accidental traumatisms and the effect of tapping methods which enable Hevea to modulate outflow of latex and hence yield. Shortly after the establishment of selected populations, it appeared that high sensitivity to Brown Bast was a hereditary feature. In 1969, Milford defined the plugging index, clonal feature linked with production and thus to sensitivity to bark dryness.

In Gabon, two major species of Loranthaceae, Phragmanthera capitata (Sprengel) Balle and Globimetula braunii (Engl.) Danser to a lesser extent, parasitize Hevea brasiliensis (Mull.) Arg. The behavior of different clones of rubber trees facing the Loranthaceae parasitism has been studied in the large industrial plantation of Mitzic and in three neighboring smallholding plantations. The clones PR 261, RRIM 600 and PB 260, although never totally resistant, are far less susceptible to Loranthaceae than the clones AVROS 2037, PB 217, PB 235 and GT 1. The parasite development kinetics was more rapid on the most susceptible clones. Phellem thickness, cortical parenchyma thickness and tannin cell density were independent of susceptibility. The number of tree ramifications was significantly different between the clones. Interestingly, on the least susceptible trees, being also the most ramified, the parasite showed the slowest development.

Ethylene stimulation with ethephon (2-chloroethylphosphonic acid) is nowadays essential for increasing latex production in the rubber tree (Hevea brasiliensis): both small-scale planters and agro-industrial plantations worldwide use ethephon. Ethylene stimulation strongly influences cumulative yield and latex cell biochemistry. The purpose of this study was to characterize the long-term behaviour of the rubber tree under ethephon treatment. Over a period of 7 years in Cote d’Ivoire, West Africa, the effect of eight frequencies of ethylene stimulation on yield and latex cell biochemistry was compared in four rubber trees clones, IRCA 130, IRCA 230, GT 1, and PB 217. The ability of the trees to produce more latex under ethylene stimulation was related to the sucrose and inorganic phosphorus contents of the latex cells. For high-yield clones with low sugar content and high inorganic phosphorus content like IRCA 130, namely quick starter clones, no stimulation was necessary to improve yield. For clones like IRCA 230, with higher sugar content, eight ethylene stimulations per year was the optimum frequency to obtain the highest yield. The effect of ethylene stimulation on latex yield increase was significant in clones with high sucrose content and low inorganic phosphorus content such as PB 217. These clones, namely slow starter clones, needed more stimulation to produce more, but in the longer run there were no negative effects of ethylene on the latex yield. These results will help planters optimize latex production by choosing the most appropriate ethylene stimulation to clones according to their latex cells biochemistry.

Dans cette étude, nous nous interrogeons sur la manière dont les conditions de commercialisation du caoutchouc naturel influencent le développement du secteur hévéicole villageois au Cameroun. Pour cela, nous analysons les résultats de deux enquêtes réalisées en 2002 et 2004 auprès de petits planteurs d'hévéa dans la province Sud-Ouest. Les résultats montrent que les conditions de commercialisation observées conduisent à des pratiques qui ont des conséquences financières défavorables pour les planteurs, notamment en terme de trésorerie. Même si, durant la période étudiée, les problèmes ont été accentués par le bas niveau de prix jusqu'en 2002, garantir de bonnes conditions de commercialisation apparaît comme une étape essentielle et un préalable obligé du développement des plantations villageoises d'hévéa.