Biological threats to natural rubber production

A critical issue is the threat to natural rubber production from plant diseases, as H.brasiliensis is genetically very homogeneous: the millions of hectares of rubber plantations are all derived from a small sample of seeds collected in Brazil by Dr. Henry Wickam in 1876 (Davis, 1997). Therefore, plant diseases are an important theme, which can be illustrated by the following example. 13 In 1934, South American Leaf Blight (SALB) wiped out the production of rubber in Brazil, and it has not been possible to restart large-scale production due to the endemic leaf blight pathogen Microcyclus ulei. The present production on marginallands in Brazil, where SALB is less of a problem, is only 96,000 T/Y, or about 1% of world production.

Accidental spread of SALB in South-East Asia could reduce production by millions of tons in a matter of years, leading to serious shortages, and consequently drastically higher prices. Attempts in the 1980s and 1990s in Brazil to develop SALB resistant Hevea clones have not met with success. Although some progress has been made (Le Guen et al., 2003), all promising lines finally succumbed to the fungus in the field (Lespinasse et al., 2000). 

A part from efforts in Asia on common plant diseases, yield, and agronomics, H. brasiliensis is studied in France and Brazil to generate leaf-blight resistant varieties, increased yield, and altered properties. Recently, efficient transformation of calli and regeneration of plants was shown to be possible (Blanc et al., 2006). 

Several genes involved in rubber synthesis have also been cloned. For example, a recent patent (Hallahan and Keiper-Hrynko, 2003) describes H. brasiliensis genes involved in isopentenyl diphosphate biosynthesis. However, the narrow genetic base, prolonged breeding cycles and juvenile period, and highly heterozygous nature of H. brasiliensis make breeding complex, time-consuming and labour-intensive. In view of the critical importance of rubber, these efforts appear rather limited.