The apphcability of random amplified polymorphic DNA (RAPD) markers in the cultivated rubber tree, Hevea, was evaluated using 43 decamer oligonucleotide primers in a set of 24 clones selected in different South-East Asian countries. A total of 220 0.35-3.5 kb DNA fragments were amplified, of which 111 were polymorphic. Of these, 80 fragments (RAPD markers) which were repeatable and clearly scorable across all genotypes were used to estimate genetic distances among the clones tested. The estimated genetic distances ranged from 0.05 (RRll 308 and PB 5/51) to 0.75 (RRIC 100 and SCATC 88-13). A mean genetic distance of 0.5 indicates a rather high genetic variability among the tested clones. As expected, because of the breeding history of Hevea, UPGMA cluster analysis and Principal Coordinate Analysis (PCoA) indicated the absence of a distinct geographical grouping. The possible application of RAPD markers for clone identification and also for analysis of genetic relationships among Hevea clones is discussed.

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Seven Hevea brasiliensis clones were evaluated on two types of rootstocks, assorted seedling rootstocks (AR) and monoclonal rootstock (MR) over 19 years. Influence of rootstock on scion growth and rubber yield was assessed based on juvenile height, circumference of the main trunk (cm), number of branches, branching height and cumulative dry rubber yield (g per tree per tapping, conventionally abbreviated gt-1t-1). Highest cumulative yield (g per tree per tapping) over the 12 years for which the trees were tapped was obtained from clone RRII 105 (MR: 1076 g per tree per tapping and AR: 497 g per tree per tapping), followed by RRII 203 (MR: 661; AR: 538), RRII 208 (MR: 477; AR: 486), RRII 118 (MR: 497; AR: 452). Gl 1 yielded the least, 219 g per tree per tapping (MR) and 378 g per tree per tapping (AR); GT1 produced 335 g per tree per tapping (MR) and 375 g per tree per tapping (AR). RRII 118 had the greatest circumference at age 19 (91.4 cm on MR) 88.8 on AR, followed by RRII 105 (MR: 87.4 cm AR: 89.2 cm) and GT 1 (MR: 88.5 cm; AR: 84.4cm). Effect of scion clone was significant (p<0.01) only for trunk circumference at opening, but not for cumulative rubber yield at age 11 (4 years after opening) or cumulative rubber yield at age 19 (12 years after opening). Most importantly, rootstock and clone × rootstock interaction did not significantly affect rubber yield or tree circumference at any evaluation time. There was no evidence to suggest that growth and yield of clones was influenced significantly by rootstock type.

Para rubber (Hevea brasiliensis), a native of the Amazon forests of South America, is the chief source of natural rubber in the world. With the objective of broadening the original gene pool collected by Sir Henry Wickham in 1876, the International Rubber Research and Development Board (IRRDB) made a large collection of wild germplasm from Acre, Rondonia and Mato Grosso states of Brazil in 1981, which was distributed to various member countries including India for conservation and evaluation. In the present study, variability was assessed in a set of 195 Hevea accessions belonging to the wild gene pool in India, using 22 characterization descriptors and eight quantitative growth characters in the juvenile stage. The Shannon-Weaver diversity indices worked out for each of the 22 qualitative traits indicated a high level of diversity in the collection. The range of variation for quantitative traits viz., plant height (0.43 to 3.16 m), basal diameter (0.81 to 2.52 cm), number of whorls (1.23 to 5.48), inter-node length (4.11 to 45.26 cm), number of leaves (11.44 to 91.26), single leaf area (80.22 to 223.57 cm2), total leaf area (2356.00 to 14660.50 cm2) and leaf area index (0.24 to 1.47), also represented wide variability in the collection. The accessions were ranked for overall performance and top 10% were selected for early growth vigour. The high level of variability observed in this germplasm indicates its potential use in crop improvement programmes and for broadening the genetic base of Hevea.