Low Genetic Variation Among Trees in Cocoa Hand Pollination in the Offinso Municipality of Ghana Revealed by SSR Markers.

Cocobod introduced nationwide artificial hand pollination in Ghana in 2017 to supplement natural pollination of Theobroma cacao L. (cocoa) by insects (Forcipomyia midges) to increase yield. Hybrid farms of 8-20 years old are mostly selected. Pollen donor and receiver trees are selected based on morphological characteristics. This study analyzed the genetic diversity among donor and recipient trees of cocoa hand pollination in three farms in the Offinso Municipality of Ghana using SSR markers. Twelve forward and reverse primer pairs out of fifteen primers screened were used to evaluate genetic intraspecific and interspecific diversity among 25 accessions based on clear amplification and reproducible scorable bands. A total of 115 polymorphic bands were detected which ranged between 5.00 and 17.00 with a mean of 9.58 alleles per locus. Cluster analysis showed similarity coefficient range of 0.10 to 0.83. Analysis of molecular variance (AMOVA) showed13% genetic variation between populations and 87% within populations of T. cacao. PhiPT value of 0.130 recorded showed weak genetic differentiation between populations. Gene diversity varied from 0.64 to 0.88 with primers MTcCIR33 and MTcCIR07 respectively. Highest observed heterozygosity (Ho) of 0.60 and least Polymorphism Information Content (PIC) of 0.57 were recorded. Pollen donor and recipient trees selected from the same or nearby farms accounts for present genetic structure of low genetic diversity between populations. Though hand pollination designs focus much on high yields, improving genetic diversity to prevent inbreeding in cocoa is recommended.