Analysis of growth, oil yield, and carvacrol in Thymbra spicata L. after slow-growth conservation

Growth, oil yield, and carvacrol content in Thymbra spicata L. Var. Spicata microshoots were analyzed after 12 weeks of storage in MS media supplemented with elevated levels (0.0, 0.1, 0.2, 0.3, and 0.4 M) of three osmotic agents (sucrose, sorbitol, and mannitol) or ABA (0.0, 3.8, 7.6, and 11.4 μM). The obtained results revealed that using 0.2 M sucrose in the storage media yielded the best results in terms of growth reduction during conservation as well as maintenance of microshoot recovery at full capacity (100%) after conservation. Meanwhile, 0.1 M sorbitol or mannitol in addition to 3.8 μM ABA were able to reduce microshoot growth during conservation, but this was at the expense of microshoot recovery after subculture to normal tissue culture conditions. The results also showed that total yield of volatile oils extracted from the dried microshoots prestored in 0.2 M sucrose produced 6.0% oil yield, which was very close to the quantity obtained in the wild mother plant and much greater than the oil yields extracted from the microshoots prestored in the other conservation treatments. Similarly, the maximum carvacrol level (9.7 × 10-4 M) was obtained in microshoots prestored in 0.2 M, sucrose which was even higher than the carvacrol amount extracted from the wild mother plant itself.