Effects of partial dehydration of recalcitrant Haemanthus montanus zygotic embryos on vigour of recovered seedlings

Cryopreservation is the most promising route for the long-term conservation of recalcitrant seed germplasm. Partial dehydration is a standard pre-treatment for the cryopreservation of zygotic embryos or embryonic axes excised from recalcitrant seeds since it reduces the likelihood of lethal ice-crystal generation during cooling. However, there is presently little to no understanding of how pre-conditioning treatments such as partial dehydration imposed at the embryonic stage are translated or manifested during subsequent in and ex vitro seedling growth. The present study assessed the vigour of seedlings recovered from partially dried (D) zygotic embryos, excised from recalcitrant Haemanthus montanus (Baker) seeds. Seedlings recovered from fresh (F) and partially dried (D) embryos in vitro, were hardened-off ex vitro, and subsequently subjected to either 42 days of watering (W) or 42 days of water deficit (S). The adverse effects of partial dehydration on seedling dry mass accumulation observed after 60 days in vitro growth did not disappear with an extension of the in vitro growth period but did appear to be reversible during ex vitro growth. A water stress during ex vitro growth dominated over the effects of embryo pre-treatment with relative growth rates in FS-seedlings (recovered from fresh embryos and subsequently stressed) and DS-seedlings (recovered from dried embryos and subsequently stressed) being statistically comparable. D- and F-seedlings responded typically to the water stress but DS-, compared with FS-seedlings, appeared to have incurred permanent damage to their photosynthetic machinery, were exposed to lower predawn water potentials, were less efficient at adjusting leaf water potential to meet transpirational demands, did not exhibit signs of osmotic adjustment, failed to adopt growth patterns that reduce transpirational water loss, and were more susceptible to persistent turgor loss. It was therefore not surprising that ex vitro seedling mortality occurred in more DS- than FS-seedlings. These results suggest that partial dehydration of recalcitrant H. montanus zygotic embryos, even when not followed by cooling, can reduce the vigour and drought tolerance of recovered seedlings.

Research Highlights
► Dehydration of recalcitrant zygotic embryos reduced vigour of recovered seedlings.
► Adverse effects of embryo dehydration on in vitro growth werereversed ex vitro.
► Seedlings recovered from partially dried embryos were more sensitive to drought.