The majority of Hevea (Hevea brasiliensis Muell. Arg.) genetic resource in Vietnam derived from the IRRDB'81 germplasm collected in the Amazonian habitats of the genus. Random amplified polymorphic DNA (RAPD) analysis was used to examine the genetic diversity and structure of the IRRDB'81 germplasm. A total of 59 accessions from 13 different districts of the Brazilian states namely Acre, Rondonia, and Mato Grosso were brought into the study using six arbitrarily preselected primers. Sixty-five RAPD band patterns ranging in size from 0.2 to 3.0 kbp were scored for analysis. Differences in the level of DNA polymorphism among the districts and states were revealed. The percentage of the polymorphic DNA fragments calculated for 13 individual districts varied from 15.38 to 70.77%. The mean values of heterozygosity within the district varied from 0.064 to 0.264. Pairwise district Nei's genetic distance values ranged from 0.046 for Catriquacu and Itanba of Mato Grosso to 0.304 for Tarauaca of Acre and Aracatuba of Mato Grosso. The estimated values of Shannon's diversity index ranged from 0.093 for the Assis-Brasil district of Acre to 0.389 for the Jiparana district of Rondonia. The analysis of molecular variance (AMOVA) indicated that most of the genetic variations were found among accessions within the districts, while interdistrict variance component accounted for 14.1% only. The low interdistrict differentiation probably implied an extensive gene flow among them. Both the principal coordinate analysis and UPGMA cluster analysis based on genetic distance values revealed a varying degree of separation among the districts and that conformed to geographical origins of Hevea IRRDB'81 collection.

The main objective of this research was to assess genotype × environment interactions and the stability status of 24 Hevea clones along with 2 checks in terms of latex yield and girth growth under two different environmental conditions representing for traditional and non-traditional rubber growing regions of Vietnam. Genotype × environment interactions were found to be highly significant for both latex yield and girth at opening, indicating that the latex yield and girth growth of the studied rubber clones were significantly affected by the environmental conditions of the location. Stability analyses indicated that LH 94/359, LH 91/579 and LH 94/481 were the best clones for highest latex yield and adaptability to traditional, non-traditional and both rubber growing regions of Vietnam, respectively. In terms of girth at opening, the stability analyses revealed that these clones were also accepted as the average girth growth and adaptability to both rubber growing regions of Vietnam.

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