Enhancement of in vitro Guayule propagation

A method of stimulating the in vitro propagation of polyisoprene containing plants from a nutrient medium containing polyisoprene containing plant tissue comprising the step of:

• adding to said nutrient medium an amount effective to stimulate propagation of said polyisoprene containing plant of a bioinducing agent of the formula;
• ##STR17## where R.sub.5 and R.sub.6 are selected from phenyl, --CH.sub.2 (CH.sub.2).sub.q R.sub.7 where q is an integer from 1 to 6, R.sub.7 is hydrogen;
• phenyl;
• an electron withdrawing group;
• R.sub.9 phenyl--where R.sub.9 is alkyl of 1 to 6 carbon atoms or an electron withdrawing group;
• --(CH.sub.2).sub.p OR.sub.8 or --(CH.sub.2).sub.p S--R.sub.8 where p is an integer from 2 to 6, R.sub.8 is hydrogen, alkyl of 1 to 4 carbon atoms, phenyl or phenyl R.sub.9, and R.sub.4 is hydrogen or R.sub.5, and at least one of R.sub.4, R.sub.5 and R.sub.6 has the structure:
• --CH.sub.2 --(CH.sub.2).sub.q --R.sub.7.