Effects of explant source, culture medium: Strength and growth regulators on the in‐vitro propagation of three Jamaican yams: ( Dioscorea cayenensis , D trifida and d rotundata )

Explants of tuber, meristem and vines from three widely cultivated yam species in Jamaica— D cayenensis, D rotundata and D trifida —were examined for their responses to mineral media strength, inorganic ammonium and growth regulator supplements. Tuber pieces (5mm 3 ) showed some positive growth responses but did not produce in‐vitro plantlets on all the media tested. Meristem tips of D trifida grew rapidly on basal media (BM) supplemented with either 0.1 mglitre −1 6‐benzylamino purine (BAP) and 0.01 mg litre −1 indole butyric acid or 0.2 mg litre −1 BAP and 1.0 mg litre −1 naphthalene acetic acid (NAA) producing plantlets by 28 weeks. The nodal explants grew rapidly with plantlets obtained from all the cultivars within 4 weeks. Use of young, vigorously growing vines of 8 weeks or less, as explant source, gave low contamination levels (16–25%) in culture when sterilised for 30 min in 200 g litre −1 NaOCl in the case of D trifida and 300 g litre −1 NaOCl in the case of D cayenesis prior to culturing. Initiation of growth was optimal when explants were taken from monopodial vines grown in October or January and placed on BM supplemented with 0.5 mg litre −1 BAP (BM0.5BAP). Addition of 0.5 mg litre −1 kinetin to the BM or 0.05 mg litre −1 NAA to BM0.5BAP depressed shoot production, while 5.0 mg litre −1 kinetin increased swelling of the nodal region in explants from sympodial shoots and from vines grown in March. The results suggest that nodal segments excised from young, fast growing vines of these species are the best explant source for the purpose of commercial micropropagation.