Abstract
In this work we compared the effect of the growth regulator content of the culture medium on the growth of in vitro shoot tips of five yam accessions belonging to four yam species (one Dioscorea alata, one D. rotundata, one D. cayenensis and two D. trifida). Medium S contained 0.6 μM benzyl adenine, 1.07 μM naphthalene acetic acid and 0.23 μM gibberellic acid while medium EBR contained 0.23 μM gibberellic acid and 0.1 μM 24-epibrassinolide. After 2 months of culture, oxidation level was significantly reduced on medium EBR compared to medium S for four of the five accessions tested. By contrast, medium EBR did not have any positive effect on shoot length since length of shoots produced after 2 months of culture on medium S and EBR were similar, except with accession 3-45T, for which shoot length was shorter on medium S compared to medium EBR. These results underline the potential of 24-epibrassinolide to reduce oxidation phenomena during in vitro culture and call for its utilization for regeneration of cryopreserved yam shoot tips, which is often impeded by oxidation phenomena.
Highlights
Cryopreservation currently is the only safe and cost-effective option for long-term conservation of vegetatively propagated plants such as yam [1]
This study was performed using in vitro shoot cultures of three yam accessions provided by the International Institute of Tropical Agriculture (IITA, Ibadan, Nigeria) including accessions N 1454 (D. alata), N 2790 (D. cayenensis) and N 3675 (D. rotundata) and of two accessions provided by the Institut National de la Recherche Agronomique (INRA) Guadeloupe, French West Indies (D. trifida accessions N 278 and 3-45T)
Studying the effect of the culture medium on the growth of each individual accession revealed that shoot length was lower after 1 month on medium S compared to medium EBR for three accessions (1454, 278 and 3-45T)
Summary
Cryopreservation (liquid nitrogen, −196 ̊C) currently is the only safe and cost-effective option for long-term conservation of vegetatively propagated plants such as yam [1]. Cryopreservation experiments performed in IRD Montpellier with American yam (D. trifida) shoot tips showed that, even though positive results were obtained, no reproducible protocol was yet available for this species (Engelmann-Sylvestre et al unpublished results). In all these reports, the authors mentioned that if high survival could be consistently achieved, regeneration of whole plantlets from cryopreserved shoot tips was variable, depending on the species and the technique used, and was generally much lower than survival. The occurrence of severe oxidation phenomena was consistently reported
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