LAUSR

Abstract Red pulp color of Tubtim-Siam pummelo (Citrus maxima Burm.) is a distinct specific characteristic, which is the preferred in the international market. This present study aimed to determine (1) the influence of tree age on carotenoid accumulation during fruit development, and (2) the carotenoid profile and related biosynthesis gene expression in “Tubtim siam” Pummelo fruit. Fruit were selected randomly from all directions of the tree at different stages of fruit development during the months of June, that is 3 months after fruit setting (3MAFS) to October (7MAFS). The carotenoid profile in the fruit pulp observed include lycopene, β-carotene, zeaxanthin and lutein. From breaker stage to commercial harvesting time, the 8-year old tree fruit observed a significantly higher ration of lycopene, β -carotene, total carotenoid concentrations and higher a* value compared to fruit in 12-year old tree. The expression of carotenoid biosynthesis genes profile in pulp of 8-year old tree fruit revealed the up-regulation of CsPSY, CsZDS and CsZEP gene expression during development and down-regulation of CsβLCY, CsβCHX and CseCHX gene expression after breaker stage (5MAFS); that appeared to be a key factor triggering lycopene accumulation because these were the key genes expressed during fruit development.