In vitro Culture of Wedelia trilobata Hairy Roots and Effect of Their Extract on Seed Germination

The effects of carbon and nitrogen sources and inorganic phosphorus concentrations on the growth of Wedelia trilobata hairy roots were investigated, as well as the effect of their extract on seed germination. The results showed that when cultured with sugar content less than 5%, the best growth of W. trilobata hairy roots was obtained with glucose as carbon source, followed by sucrose, while with the sugar content more than 5%, only maltose was able to promote the hairy root growth. However, when maltose concentration was higher than 7%, the growth of hairy roots was also gradually inhibited. The best stimulating effect on the growth was obtained when (NO_3)~--N (263.1 μg/mL) was combined with (NH_4)~+-N (577.2 μg/mL) or supplemented with inorganic phosphorus content 2~3 times the amount of inorganic phosphorus in MS medium. When cultured without addition of Ca~(2+) into the medium, the hairy roots had vigorus growth with many branches and became thinner, but with the increasing concentration of Ca~(2+), their growth was suppressed. The inhibitory effect of seed germination was higher when the seeds of rice (Oryza sativa L.), Bidens pilosa L., and crabgrass were soaked with ethanol-soluble extract, than that of those treated with water-soluble extract. Compared to the control, when soaked with water-soluble extract of hairy roots, the seed germination rates of rice, B. pilosa and crabgrass were 84%, 93% and 20%, respectively, but when soaked with ethanol-soluble extract of hairy roots, the seed germination rate of crabgrass seeds was 3%, but no seed germination of rice and B. pilosa was observed The seed germination was more inhibitory when with ethanol-soluble extract of hairy roots than that of wild roots. When the seeds of rice, B. pilosa and crabgrass were soaked with ethanol-soluble extract of light-cultured hairy roots, their seed germination rates were 28.7%, 3.9% and 18.7%, respectively, and were higher than those with ethanol- soluble extract of dark-cultured hairy roots, with which the seed germination rate was 4% for rice and 1% for crabgrass, but no germination for B. pilosa,This experiment provides the solid experimental and technological foundation for selecting optimal conditions for large scale culture of W. trilobata hairy roots, and for producing secondary metabolites and further application of the secondary metabolites to eliminate weeds in agriculture. Fig9, Tab1, Ref19