The use of self-pollinated progenies as 'in-groups' for the genetic characterization of cocoa germplasm

The value of molecular biology for the curating of large germplasm collections is limited by several practical considerations. The molecular method employed should be quick, inexpensive and technically simple, but must also be sufficiently informative to distinguish between most of the stocks held. The overall strategy for the genetic evaluation of a collection needs to identify mislabelled accessions and, at the same time, enable priorities to be established for the maintenance or removal of material. In the present study, the potential of ISSR-PCR analysis is assessed for the maintenance and genetic characterisation of an international collection of cocoa (Theobroma cacao) genotypes. Six primers were sufficient to distinguish all but three pairs of the 62 accessions examined. A UPGMA dendrogram was used to provide a measure of the genetic variability between genotypes. The scale was supplied by the inclusion of Theobroma grandiflora as an 'out group' and also by the use of two contrasting progenies as 'in groups'. The 'in groups' were obtained from the self-pollination of one plant (SPEC 54.1) known to be highly homozygous and also of a second, highly heterozygous, clone (P 19B). These reference points allowed several documentation errors to be resolved and provided a basis for identifying unwanted or low-priority material. Implications of the work for the routine maintenance of large germplasm collections are briefly discussed.