Scientific research

We studied the functional relationship between pollination intensity and fruit survival as well as the number of seeds per pod in the tropical tree Theobroma cacao L. on a Forastero Upper-Amazon clone (UPA 409) in Ivory Coast. Cutting the style 24 h after pollination allowed for counting the number of pollen grains deposited on a stigma without affecting fruit set and seed development. Forty-three pollen grains were necessary to reach 50% of maximum fruit set 28 days after pollination. Above 115 pollen grains, the proportion of developing ovaries reached a maximum of 88% 28 days after pollination and 75% at maturity. With fewer than 238 pollen grains per stigma, there was a close relationship between pollination intensity and number of seeds per pod; the pollen:seed ratio increased from 1.6:1 to 3.8:1 for PI increasing from 30 to 238 pollen grains. For higher pollination intensities, the average number of seeds per pod reached a maximum of 58. The relationship between pollination intensity and seed content was modelled. Results are consistent with the hypothesis that ovules attracted pollen tubes in a similar way regardless of whether or not they had already been reached by another pollen tube.