Changes in germinability and desiccation-sensitivity of recalcitrant Hopea hainanensis Merr. et Chun seeds during development

During their development front 80 to 169 days after anthesis (DAA). seeds and their embryonic axes of Hopea hainanensis undergo changes in morphological characteristics, germinability, moisture content and desiccation tolerance. For both seeds and their embryonic axes, fresh and dry weight as well as volume increase very rapidly front 122 DAA to 136 DAA and reach maxima at 157 DAA, then decline. From 80 DAA to 94 DAA, the moisture contents of seeds and their embryonic axes increase, then gradually decrease after 94 DAA. From 136 DAA to 169 DAA, the germinability of freshly harvested seeds is very low, but slowly increases thereafter and is improved by rapid drying. Freshly excised embryonic axes at 122 DAA have high germinability and their viability following 2 h of rapid drying gradually increases from 122 DAA to 150 DAA, then declines thereafter. Viability measurements and electrical conductivity analyses after drying treatment showed that front 122 DAA to 157 DAA, the desiccation tolerance of seeds and their embryonic axes gradually increases and reaches a maximum at 150 DAA before declining. Based on these results, 157 DAA seeds could be considered to be physiologically mature. Nonetheless. the desiccation tolerance of immature seeds collected before 150 DAA is greater than that of those seeds harvested after 157 DAA. From 157 DAA to 169 DAA. rapidly dried embryonic axes survive to lower water content compared with slowly dried ones.