Cross-pollination with native genotypes improves fruit set and yield quality of Peruvian cacao varieties

Authors: VANSYNGHEL, JUSTINE - University Of Wurzburg; THOMAS, EVERT - Alliance Of Bioversity International And The International Center For Tropical Agriculture (CIAT); OCAMPO-ARIZA, CAROLINA - Georg August University; MAAS, BEA - University Of Vienna; Zhang, Dapeng; ULLOQUE-DEWENTER, CARLOS - Universidad Nacional De Piura; STEFFAN-DEWENTER, INGOLF - University Of Wurzburg

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2023
Publication Date: 7/25/2023
Citation: Vansynghel, J., Thomas, E., Ocampo-Ariza, C., Maas, B., Zhang, D., Ulloque-Dewenter, C., Steffan-Dewenter, I. 2023. Cross-pollination with native genotypes improves fruit set and yield quality of Peruvian cacao varieties. Agriculture, Ecosystems and Environment. https://doi.org/10.1016/j.agee.2023.108671.
DOI: https://doi.org/10.1016/j.agee.2023.108671

Interpretive Summary: Pollination is essential for cacao tree to produce cacao beans. Although a cacao tree can produce a large number of flowers, no more than 10% of the flowers produced are naturally pollinated, resulting low yield in cocoa production. Hand pollination, whereby pollen is supplemented to flowers by hand, is increasingly being explored as a strategy to overcome pollination deficit. However, abiotic stresses are expected to limit the benefit of hand pollination, because these stresses can reduce the carrying capacity of cacao tree. In the present study, we compared manual self-pollination with cross-pollination using five fine-flavor cacao genotypes as pollen donors. Simultaneously, we assessed the effect of soil water content, temperature, and relative humidity that influenced fruit set and bean quality. Our result showed that the success of cross-pollination mainly depended on the compatibility between the pollen donor and receptors. In addition, cacao bean weight was higher in fruits resulting from manual pollination than from natural crosses. Moreover, fruit set was also affected by temperature and relative humidity. Together, our findings suggest pollination deficit is the main factor affecting fruit set, but water and temperature stress also contribute to low fruit set. Our results suggest optimizing natural cross by planting cross-compatible and fine-flavor genotypes in grids-like field arrangements. The strategy of improved genotype spatial deployment would be more cost-effective than artificial pollination for cocoa yield increase. This information will be used by cacao breeders, agronomists and growers to select fine flavor cacao genotypes and design effective practice for crop management.

Technical Abstract: Pollination deficit has been suggested as one of the most important factors limiting cacao productivity. Artificial pollination management is a potential solution to increasing crop productivity. However, in most cocoa producing regions, abiotic stresses are expected to limit the benefit of hand pollination. Here we compared manual self-pollination with cross-pollination using five native Peruvian genotypes as pollen donors. Simultaneously, we assessed how soil water content, temperature, and relative humidity influenced fruit set and evaluated quality difference of cacao beans between manually and naturally pollinated fruits. Success of self-pollination was very low (0.5%) but increased 3 to 8-fold in cross-pollination experiments. The success of cross-pollination depended on the genotype of the pollen donor, irrespective of genetic similarity between pollen donor and acceptor. Further, bean weight and percent of premium beans were higher in manually pollinated fruits than naturally pollinated ones. In addition, we found that fruit set was significantly affected by temperature and relative humidity, as well as their interactions with pollination methods. Together, our findings show pollination deficit is the main factor affecting fruit set, but limitation in water and temperature stress can also reduce the carrying capacity of the studied native cacao trees. Our results indicate that selecting cross-compatible genotypes with good sensorial quality and grow them in grids-like field arrangements would be more cost-effective than artificial pollination.