CARBON-DIOXIDE TREATMENT PARTIALLY OVERCOMES SELF-INCOMPATIBILITY IN A CACAO GENOTYPE

Cacao (Theobroma cacao L.) contains self-compatible and self-incompatible genotypes. In the greenhouse, pollen germination and fruit set failed to occur after self-pollination of an incompatible genotype (IMC 30); however, if the self-pollinated flowers were enclosed in plastic vials for 6 h after pollination, pollen germination was 95%. The promotive effect of enclosed pollination on pollen germination was due to the accumulation of CO2 (8.9 % v/v). Despite the high rate of pollen germination, fruit set was only 45%. Seeds produced from self-pollinations using this technique were viable, with 95% germination. Cross-pollination with 'Amelonado' pollen resulted in 100% pollen germination and 46% fruit set. Enclosure of cross-pollinated flowers did not improve the percentage of fruit set. Sections made through the ovary 48 h after enclosed self-pollination indicated that the majority of ovules contained a zygote; however, some ovules still contained unfused male and female gametes and polar nuclei. Self-incompatibility in this genotype is expressed at two stages in the process leading to fruit set. The first is at the pollen germination stage and can be overcome hy CO2 treatment; the second is at the gametic fusion stage.