Mythbusters is pop science, junk science, not really science. It's not a credible source for anything save entertainment.
I think Feynman would disagree http://xkcd.com/397/
the point is there are showing what the spirit of science is. Which, is good.

It's not just Backster that has done this the work is there to be done and recorded, and the results so far are worthy of even more study.
Backster is just a new age quack. He hasen't published in any peer reviewed scienctific journals.
Backster's claims were refuted by Horowitz, Lewis, and Gasteiger (1975) and Kmetz (1977). Kmetz summarized the case against Backster in an article for the Skeptical Inquirer in 1978. Backster had not used proper controls in doing his study. When controls were used, no detection of plant reaction to thoughts or threats could be found. These researchers found that the cause of the polygraph contours could have been due to a number of factors, including static electricity, movement in the room, changes in humidity, etc.
http://www.skepdic.com/plants.html

Backster is wrong. Atleast Mythbuster actually use the Scienctific method.