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

The cacao tree (Theobroma cacao) is a billion-dollar crop species of which the yields are greatly constrained by, amongst others, pollination limitation. Manual pollen supplementation has been proposed to counter pollination deficits, thus improving yield quantity and potentially also quality, as the origin of the pollen can be controlled. In native cacao, low self- and cross-compatibility rates and the interaction with abiotic growth conditions are expected to limit manual pollination benefits. Here we compared supplementation of self-pollen with cross-pollen of five native genotypes selected for their sensorial quality as pollen donors. Simultaneously, we assessed how temperature, relative air humidity and soil water content influenced fruit set and evaluated qualitative differences between pollen-supplemented and open pollinated fruits. Success of manual self-pollination was very low (0.5 %) but increased 3–8-fold in cross-pollination experiments. Cross-pollination success rates depended on the genotype of the pollen donor, irrespective of genetic distance between pollen donor and recipient. Further, seed weight and premium seed content was higher in fruits resulting from pollen-supplemented than from open-pollinated flowers. Fruit set was also affected by the interaction of temperature and relative humidity, but not by soil water content. Together, our findings suggest that reproductive traits of native cacao systems are constrained by genetic compatibility and some abiotic factors. Even though manual pollen supplementation with native genotypes can clearly benefit both fruit quantity and quality, it is labor intensive and hence costly to implement. Natural cross-pollination by planting compatible genotypes selected for sensorial quality could simultaneously avoid high costs and improve fruit quality, potentially resulting in net economic gains for smallholder farmers.