Volume 18 2026 SELF- AND CROSS-INCOMPATIBILITY IN COCOA (THEOBROMA CACAO L.): A CONCISE REVIEW Authors Johnsiul, L.1*, Rahman, M.Z.A.1, Norasekin, T.1, Ishak, Z.2, Roslina, M.S.1 & Durahman, D.R.1 ABSTRACT Reproductive incompatibility is a critical yet often underestimated contributor to the Theobroma cacao L. yield gap, and the only major constraint to be fixed at planting. This review examines the literature from 1927 to 2026 to establish the factors contributing to this reaction, yield costs, and strategies that could be taken to overcome the problem. It is reported that, in a late-acting system, while pollen germination and tube growth are indistinguishable from compatible matings, gametic fusion fails within the embryo sac. Genetically, this multi allelic S-locus system prevents closely related clones from sharing alleles by pollinating one another. As a result, monoclonal or poorly designed polyclonal blocks may suffer low pod yield despite abundant flowering and pollinator activities. The retention indices reported across studies vary from 0% to 87.5% across parental combinations. Incompatibility, pollen limitation, and resource constraints are found to act multiplicatively rather than additively. Thus, field diagnosis, verified compatible clonal arrangements, and side-grafting are reported to be the cost-effective interventions that must precede pollination and nutrition inputs. VIEW PDF DOWNLOAD