Core collection of Hevea brasiliensis from the 1995 RRIM Hevea germplasm for effective utilisation in the rubber breeding programme

摘要

The rubber tree (Hevea brasiliensis) is the world's major source of natural rubber. An expedition to the Amazonas and Para states by the Rubber Research Institute of Malaysia (RRIM) in 1995 led to the successful collection of more than 50,000 genotypes from different locations of the states to broaden the existing gene pool. Realising the severe limitations faced with large germplasm, a core collection consisting of a reduced number of genotypes derived from a base collection of 505 selected genotypes was developed. The genotypes were first sorted based on their relative contributions to the total variability by principal component scores of a set of 11 quantitative traits. Then, the cumulative proportion of their contributions to the total variance was computed. The size of the core set was decided by a cut-off value when the rate of increase in cumulative contributions reached a maximum value and began to decline. Entries with a high degree of similarity in the selected core collection were eliminated using Gower metric coefficient. Shannon-Weaver diversity index of 14 morphological qualitative descriptors was used to verify the size and choice of entries in the final collection. As a result, 25.35% of the base collection or a total of 128 genotypes (73 from Manaus, 17 Manicore, 13 Atalaia do Norte, 11 Borba, 8 Benjamin Constant, 3 Tapajoz, 2 Belem, and 1 Iranduba) were selected to be included in the final core collection. Establishment of the core collection of this germplasm will enable a more rapid and effective utilisation of these genetic materials in the rubber breeding programme.