Shoot initiation by humic acids of selected tropical crops grown in tissue culture

The effect of humic acid on shoot development from nodal segments in tissue culture was tested. The species wereGnetum gnemon, Elletaria cardamomum, andPogostemon cablin. Humic acids were extracted from a peat soil sampled from South Sumatra, Indonesia. Alkaline extraction was conducted on two series of 12-hour agitations followed by centrifugation and sedimentation at pH below 2. Explants were 1-cm long single nodes ofG. gnemon andP. cablin, and lateral buds ofE. cardamomum on MS medium. Benzyladenine was added at 0.1 mg/L for the first two and at 0.3 mg/L for the latter. The treatments included six, seven, and eight levels of humic acid concentrations for the respective species in a completely randomized design with 10 replicates. Effect of the treatment was evaluated on the basis of the initiation period of shoots and/or roots, and the number and height of the shoots. The initiation period of the shoots was significantly shortened in the presence of humic acids. Root initiation was significantly induced especially when humic acids were used in liquid medium. In combinations with BA, the addition of humic acids at 400 mg/L, 40 mg/L, and 300 mg/L yielded the fastest growth ofG. gnemon, E. cardamomum, andP. cablin, respectively.