USE OF RAPDs FOR ESTIMATION OF GENETIC DISTANCES BETWEEN POPULATIONS OF THE COCONUT PALM

Abstract

Accurate estimation ofgenetic distances between and within species is vital inthe conservation of' heterogeneous tree populations, such as coconuts. Coconutgermplasm is being conserved at present by the selection and preservation ofecotypes and in biased collections that are based on economic traits; suchselections are likely to misrepresent the natural variability ofthe palm. To helpin improving conservation methods, a DNA fingerprinting system, RAPDs(Random Amplified Polymorphic DNAs) is proposed.

R4PDs were investigated in 19 coconut types planted at the Coconut ResearchInstitute, Sri Lanka, by using random primers of 10-12 nucleotides. Extracts of'DNA front the leaves (if jour individual trees were pooled to represent eachheterozygotic coconut type. Thirty-eight primers were tested in the RAPD-PC'R*and polymorphic bands and scoredfor presence or absence in each type. Pairwisegenetic distances were calculated according to Nei and Li's coe.fJicient, andcluster analysis was performed on the basis of the resultant distance matrix.

Eighteen primers detected a total 91 polymorphic hands across the coconuttypes screened. All these RAPDs were clear and reproducible over repeatedruns. (Trouping of 19 coconut types based on these RAPDs matched thecurrently accepted taxonomic grouping almost perfectly. This good matchindicates that the RAPDs method is applicable as a sound genetic marker fl.lr thecharacterization of' coconut genetic resources. The technique is simple andrapid. It can be developed without previous information about the DNA of thetarget plant. The cost is affordable [or developing countries. The technique isnow widely applied in the breeding and conservation of' heterozygous perennialcrops andforest trees.