Plant Materials. The bulk of the mature leaf tissue collected from a 26-year-old single individual rubber tree grown in an outdoor field at the Department of Biology, Faculty of Science, Khon Kaen University was used for comparison. Mature leaves sampled from nine accessions of rubber tree from Sakon Nakhon, Loei and Khon Kaen provinces and seventeen species of tropical plant plants from Khon Kaen province were also conducted to confirm the effectiveness of the protocol.