The effects of jasmonic acid (JA) applied in the medium and its methylester (MeJA) applied either in the medium or as a vapour, on shoot growth and microtuber formation were evaluated in three important food yam species (Dioscorea alata, D. cayenensis, and D. rotundata). Single nodes with leaves, derived from in vitro-multiplied material, were used as explants. When delivered at higher concentrations (10 or 50 μM) both JA and MeJA suppressed node formation. Microtuberisation was supported in all three species by adding either JA or MeJA to the medium. Significant promotory effects were observed only when photoperiod, salt compositions and sucrose concentrations known to favour microtuberisation processes in yams were used. MeJA applied as a vapour strongly inhibited microtuber differentiation in D. alata on all media tested but in D. rotundata and D. cayenensis yams MeJA, also applied in the vapour phase, exhibited slight promotory effects on microtuberisation.
Keywords: Dioscorea; Jasmonic acid; Key words Food yam; Methyljasmonate; Microtuber formation.