Fingerprinting of black pod disease-resistant theobroma cacao L. accessions using microsatellite molecular markers

Abstract

Black pod is a disease of Theobroma cacao L. and can cause up to 100% losses in crop yield. Breeding for resistance can reduce or prevent the incidence of the disease. This study was therefore designed to assess black pod disease resistance in 205 accessions of five populations; ‘T’ clones, progenies of ‘T’ clones, Amazonia, Series II hybrids and a control population of susceptible accessions by the leaf disc method and genetic fingerprinting using 13 mTcCIR microsatellite molecular markers. Scores from the leaf disc test were 1.24, 1.50, 1.68, 1.97 and 3.33 for the ‘T’ clones, progenies of ‘T’ clones, Amazonia, Series II hybrids and the controls respectively. This indicates that the ‘T’ clones were the most resistant. A total of 127 alleles were detected with the mTcCIR microsatellite primers.Out of these, 23 were found unique to the ‘T’ clones. The observed (HO) and expected (HE) mean heterozygosity over all the populations were 0.625 and 0.656 indicating a heterozygote deficit among these populations despite the high genetic variability. Cluster analysis also indicated low genetic diversity among populations but a high genetic difference between individuals within a population.Therefore, the ‘T’ clones could be employed in breeding for resistance to the black pod disease. The unique and rare alleles found in the ‘T’ clones could have accounted for their high resistance. The low genetic base observed indicates the need for introduction of exotic varieties in breeding programmes to broaden the genetic base of the cocoa germplasm in Ghana.