Effect of pollen load, source and mixture on reproduction success of four cultivars of Citrullus lanatus (Thunb.) Matsumara and Nakai (cucurbitaceae)

Citrullus lanatus is cultivated in Côte d’Ivoire for its edible kernels which are used as a soup thickener. There are four distinct cultivars (one Bebu and three Wlêwlê). A better understanding of the reproduction system for those annual monoecious cultivars may improve its production. We studied the impact of pollen load, pollen source and diversity on the yield of fruits and seeds. Various pollination treatments were applied during four growing seasons to assess pollen load, pollen source and diversity (cross pollination with single source, cross pollination with multiple sources, self pollination and natural pollination) and pollen mixture. Pollination and reproductive success were determined by a fertilization index and by assessing fruits and seeds production. The self-compatibility and inbreeding depression index were also evaluated. Higher or lower pollen quantity decreases fertilization success of fruits and seeds production while medium pollen load leads to optimal yield. All cultivars were self compatible and higher level of inbreeding depression had been observed. When cross pollinated, yield was higher than natural pollination and self pollination yield. With manual pollination, cross pollination with multiple sources produces more fruits and seeds resulting in increased yield. Pollen diversity also improves fruits and seeds production. Pollen mixture will increase yield if the proportion of cross pollen in the mixture is higher than self pollen proportion. In conclusion, fruits and seeds production of those local self compatible cultivars were influenced by the amount of pollen load, pollen source and diversity, and also by proportion of pollen type in the pollen mixture. These results are therefore necessary in order to predict the evolutionary trajectory of mating systems and to make plant breeding program.