II. Analysis of genetic variation among accessions using RAPD polymorphism

The twelve selected primers generated 155 amplicons. Each band is an amplified DNA fragment. The number of polymorphic bands generated by each primer ranged from 6 (OPB-6) to (OPC-13). Besides average number of bands per accession ranged from 4.61(OPB-6) to 12.6(OPC-13). The size of the amplification products ranged from 2500bp to 100bp. Polymorphic bands were distributed across the entire molecular size range. All primers used in the study produced more number of polymorphic bands and less number of monomorphic bands. Selected 12 primers produced unique rare accession specific fragments. This depends on the genetic make up and diversity existing in the nucleotide sequence of the accessions.

All collections were classified using these 12 primers, 155 clear-cut RAPD were generated and 134 (86.45%) were polymorphic which indicated considerably high level of genetic polymorphism in the germplasm The number of bands produced by each primer varied from 6 (OPB 06) to 22 (OPC 13) with a mean ± SD of 12.92 ± 5.57 bands/primer. The size of the amplified fragments ranged from 100bp to 2500bp. Of he 155 markers generated, only 21 (13.55%) were monomorphic. Maximum numbers of polymorphic bands were resulted with the primer OPC 13.

III. Genetic relationships among accessions:

Phenogram based similarity indices: The bands scored among 76 accessions using 12 primers were utilized for estimating Jaccard's similarity coefficient and constructing dendrogram based on genetic similarity data by unweighed pair group method of arithmetic averages (UPGMA).

Nigerian collections

Jaccard's similarity coefficient estimated from RAPD markers obtained by 12 polymorphic markers range from 0.66 between NC 35 and NC 10 to 0.94 between NC 20 and NC 64. A graphical representation of genetic similarity was obtained by generation of dendrogram from the similarity matrices. Phenetic analysis resulted in 3 clusters. NC 35 and an unknown accession NC 10, whose pedigree is not known, shared highest similarity of 94%. These selections were introduced from Nigeria, where it is a cash crop and most of the produce is exported. The first cluster consists of 7 accessions of unknown origin such as NC 26, NC 27, NC10, NC 08, NC 05, NC 03 and NC 02. Other accessions in this cluster are NC 09, NC 36, NC 12, NC 38, NC 31, NC 35, NC 32, NC 46 and NC 41. This cluster has not much variation and consists of hybrids of Pound's collections and Trinitario hybrids. It appears that these are F1 hybrids and was subsequently maintained as clonal selections.