Diversity, inbreeding and inbreeding depression in rubber tree (Hevea spp.). In: Agrotrópica v. 27 p. 33-44, 2015.

Abstract

Based on pedigree information, diversity, inbreeding level and inbreeding depression were estimated among clones released to rubber producers from 1950 to 2000, by the Rubber Research Institute of Malaysia (RRIM), the Cacao Research Center (CEPEC) and the Agronomic Institute of Campinas (IAC), in Brazil. Fifty founding or primary clones were used to produce all varieties of the three breeding programs, however some of them were overused, resulting in low diversity in plantations (Ne < 22). The clones Tjir 1, PR 107 and PB 86, together, contributed on average 44% of all alleles of the 42 varieties released by RRIM and 38% of those 22 released by IAC. PB 86, F 4542 and Tjir 1 contributed 42% of all alleles of the 35 clonal varieties recommended by CEPEC. Using unpublished and published information by several authors, it was shown in this paper that inbreeding depression occurs in rubber tree. In the populations studied, yield reduced 10.1 g/tree/tapping in adult trees for each 0.1 units of increase in the inbreeding coefficient (F). Bark thickness reduced 0.8 mm per each 0.1 F, trunk girth 2.3 to 11.4 cm in mature trees and 2.4 cm in young trees. South American Leaf Blight severity increased 0.03 points, per each 0.1 F, in a scale of severity ranging from 1 (plants free of infection) to 4 (highest level of SALB infection). Based on these results, increasing diversity in the programs studied appears to be mandatory in order to reduce future depression by endogamy and the risks with disease epidemics.