Improving acclimatization through the photoautotrophic culture of coconut (Cocos nucifera) seedlings: an in vitro system for the efficient exchange of germplasm
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An in vitro photoautotrophic step based on the supply of CO2-enriched air (1,600 μmol mol−1) during the light phase and ambient air (350 μmol mol−1 CO2) during the dark phase has been used to promote the ex vitro establishment of coconut (Cocos nucifera L.) seedlings. The introduction of this step into a previously developed in vitro protocol was found to improve the quality of the seedlings (as assessed by fresh weight increase, physical stature, leaf area and thickness, stomatal density, and chlorophyll a content, and primary and secondary root production), the proportion of seedlings successfully transferred to soil (improvement from 40% to 100%) and achieved in a shorter time (reduction from 10 to 6 mo). Best results using this photoautotrophic growth step were obtained when a low medium concentration of sucrose (43.8 mM or lower) was used, when it was applied to seedlings that had already reached 4 or 5 mo of age in the in vitro culture step, and when seedlings were cultured in the photoautotrophic system for 2 mo or more before transfer to soil. Our improved protocol is more efficient and it reduces the cost per plant for the international exchange of coconut germplasm.
KeywordsPhotoautotrophic culture Coconut embryo culture CO2-enrichment International germplasm exchange
The project was partly funded by the Australian Centre for International Agricultural Research, via project HORT/1998/061. The authors would like to thank Mrs. Erlinda Rillo from the Philippine Coconut Authority, Albay Research Station, who provided the seedlings used in the experiments, and Mr. Graham Kerven and Mr. Sisunandar of the School Agriculture and Food Sciences, University of Queensland for their technical assistance on chlorophyll analysis and some aspects of manuscript preparation, respectively.
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