Quercus hintonii is an endangered species of red oak that grows in the province of Sierra Madre del Sur. It sheds acorns from August to September, when the mean monthly temperature is from 15-25°C. The acorn fruit can be considered a recalcitrant seed type, whose germination rate drops to 4.5% only 30 days after shedding. Considering how rapidly Q. hintonii acorns lose viability, it is of the utmost importance to find controlled conditions that allow the long-term preservation of viability and vigour. Herein, we propose the use of a saturated solution of magnesium chloride and calcium chloride, which provides a relative humidity of 33% upon hydration at 7°C for acorn storage. We found that the storage conditions for acorns of Q. hintonii are crucial for extending acorn survival time, preserving a higher germination rate and expanding the time needed for 50% germination, which varied between 115 and 183 days depending on the harvest. In addition, the time for germination ranged from 5 days to 14 days when the storage period was prolonged. Moreover, the vigour of seed obtained in 2004 was greater than that of the 2007 seeds, as measured by increase in survival, plant vigour, increased stem size and an increase in leaf number. The different environmental conditions during harvesting showed strong effects on seed germination and plant development, which likely resulted from moisture levels being high in 2007 compared with 2004. Thus, acorns harvested in 2004 experienced a drier environment, did not germinate in the field at that time and reached the end of the maturation phase; whereas in 2007 a greater number of acorns germinated in the field at the time of its collection. Therefore, the 2007 harvest conditions affected the time needed to equilibrate at 30% relative humidity, exposed the acorns to a greater time in the sensitivity window, deteriorated them further and diminished the germination index and seedling vigour.
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