Genetic Diversity and Erosion in Hevea Rubber

Abstract

Genetic diversity keeps the soil fertile, recycles all nutrients, and cleans the air and water. The richer the genetic baggage, the higher shall be the capacity to fight different fungi, virus, or bacteria. Like other essentials, rubber is an industrial commodity that is indispensable to humans with more than 55,000 vivid products made from it. Hevea, rubber originated in Amazon, where 1652 plants belonging to 107 species in 37 different families are found in about 630 m2. Hevea—rubber originated in such a biologically diversified environment. From the story of the first transfer of rubber seeds from Brazil to Asia, it is difficult to evaluate how narrow the genetic base initially was for what has now become the “Wickham” domesticated population. Much importance was conferred to a small number of 22 seedlings disseminated from Singapore to Malaysia after 1876, and the original Wickham stock was collected in only one Brazilian site, Boim, on the Western banks of the Tapajoz River. Though generation wise assortative mating as the prime breeding tool was applied to these accessions and Wickham collection, much genetic variation could not be tapped for commercial purpose. The molecular marker systems (all three generations markers) are being applied in Hevea rubber. Of these, SNPs are the new generation markers used for Marker-Assisted Selection (MAS). A saturated linkage map of Hevea brasiliensis has been accomplished and the whole genome size was calculated as 6 × 108 base pairs. Selection was indirectly toward nuclear DNA polymorphism, while evolving modern clones. mtDNA of Wickham clones has lesser variation because their female progenitors are all primary clones (either PB 56 or Tjir 1). Chloroplast genomes are sufficiently large and complex to include structural and point mutations that are useful for evolutionary studies from intraspecific to interspecific levels. Populations were subjected to several rounds of controlled crossing that further narrowed the diversity. But the strategy followed by the breeders to select only the desirable genotypes and to reject the unwanted ones (without assessing the utility other than yield) is the main reason that reduced diversity. Much work at the molecular level had been carried out like for Tapping Panel Dryness, latex production, defense genes and alike. Setting up of a molecular library for Hevea and scientists working worldwide contributing to this library will be a good option to study and document molecular diversity.