Response of Selected Species of Yam ( Dioscorea spp.) Vine Cuttings to Different Growing Media

Abstract

Yam, Dioscorea spp., is an important staple food in tropical regions including the Pacific. The traditional propagation technique using the whole or part of the seed tubers limits the farmers’ capacity to produce more yams. Vine-cutting method is an effective way to solve the problem of seed tuber shortage in yam cultivation. This study was conducted to evaluate the root, shoot, and tuberization potent of vine cuttings of three local yam cultivars namely, “ palai uea ”, “ palai maoi ”, and “ palai afelika ” which were coded as DN1, DN2, and DR, respectively. These cultivars belonged to the two local yam species, D. nummularia and D. rotundata grown in different growing media combinations of carbonized sawdust (CS) and sterilized topsoil (TS) as follows: 100CS:0TS, 75CS:25TS, 50CS:50TS, 25CS:75TS, and 0CS:100TS. Observations and data collection for the number and length of roots and new shoots, survival rate, and the number of minitubers initiated were first made 28 days (4 weeks) after planting (AP) the vine cuttings, followed by weekly observations and collection for a period of five weeks. There was a very significant interaction effect between the different growing media and yam cultivars on the root length (p-0.001) of vine cuttings from the three cultivars (DN1, DN2, and DR) grown in different media under nursery conditions. There was also a significant interaction effect between the different growing media and cultivars on tuber length (p-0.048) of rooted vine cuttings grown under field conditions. The combination of 50CS:50TS was the best-growing media for cultivar DN1 that favours the production of higher average root number (4.80 ± 1.48), root length (5.32 ± 2.25), and the number of shoots (1.35 ± 0.38). Cultivar DN2 responded well to the combination of 25CS:75TS where it produced the highest number of roots (5.70 ± 1.01), root length (11.19 ± 7.13), number of shoots (2.25 ± 0.82) and shoot length (11.19 ± 7.13). The combination of 75CS:25TS was the best for cultivar DR, which produced a higher average number of roots (6.25 ± 1.89) and shoots (6.25 ± 1.89). However, the combination of 25CS:75TS was more suitable for producing longer roots (10.38 ± 1.89) and shoot lengths (9.84 ± 2.79) and the number of minitubers (1.25 ± 0.25). The survival rate of vine cuttings grown in different growing media under nursery conditions ranged from 39% to 61%. Nevertheless, the survival rate for vine cuttings grown under field conditions was from 25% - 75%. The findings indicate that specific CS:TS ratios optimize growth for each cultivar under nursery conditions and that this method is a viable technique to increase the availability of yam planting materials in Samoa.