Assessment of coconut tree genetic divergence by compound sample RAPD marker analysis

Abstract

The coconut tree (Cocos nucifera L.) is a tropical species widely cultivated throughout the world, which isfound in all intertropical regions. The species shows wide phenotypic variability, which, however, is littleunderstood at the genetic level. This study of the variability among the various coconut tree populations isimportant to increase the efficiency of the development of superior cultivars adapted to different ecologicalconditions. It also helps the selection of divergent progenies that can maximize heterosis in hybridizations.Genetic divergence among 19 coconut tree populations available in the BAG - Coco at EMBRAPA/CPATC wasestimated by RAPD. Leaf samples from 21 plants of each cultivar were squashed together (compound samples)in liquid nitrogen and the DNA extracted using the modified Doyle and Doyle (1990) protocol. Samples of theseDNA were amplified with 24 primers of the OPERON Technologies series. One hundred and twenty-sevenpolymorphic and 61 monomorphic loci were obtained. Six different clusters, possibly heterotic groups, wereformed by the Tocher optimized clustering analysis which used the matrix of the complement of the Jaccardindex. Group 1 included the dwarf group cultivars. Giant accessions, abbreviated to GBR (Brazilian Giant),formed group 2, except GBRPF, which together with West African Giant (GOA) formed group 4. The mostdistant accession was the Tonga Giant cultivar (GTG) that did not group with the others and presents potential forhybridization with the six cultivars in the dwarf group cultivars and with the five in the GBR group. Group 3consisted of GRL, GPY and GRT and Group 5 of GML and GVT. The dendrogram obtained by the nearestneighbor method was in line with the clustering obtained by the Tocher optimization method. The markers usedpermitted identification of each one of the populations showing that they were genetically different (absence ofduplicity). The use of compound samples was effective to investigate the interpopulational genetic diversity.However, to understand the intrapopulation genetic variability, individual sampling should be used.