MICROPROPAGATION OF AZALEAS USING THIDIAZURON

Abstract

Rhododendron sp., deciduous azaleas are routinely grown in vitro using N°C-(2-isopentenyl)-adenine (2ip) as the cytokinin. Actively multiplying cultures of cvs. 'Gilbraltar', 'Peachy Keen', and 'Tobasco' were placed onto a woody plant medium containing various concentrations of N-phenyl-N'-1,2,3-thiadiazol-5-ylurea (thidiazuron, TDZ) to determine whether TDZ could be substituted for 2iP. The deciduous azaleas tested were highly responsive to TDZ and sensitivity varied with cultivar. Plants were grown on in vivo to observe any affect of TDZ on older plants. Thidiazuron was then tested at a wider range to determine the optimal concentration for proliferation, shoot quality, and growth. Proliferated cultures underwent a cold treatment to determine if TDZ's activity is temperature dependent. TDZ in combination with 2iP was tested to see if there was a synergistic affect using both compounds. TDZ has powerful cytokinin activity, yielding many shoots of lesser quality due to compact vitrified growth. Shoots did not elongate when exposed to cold temperatures. The combination of TDZ and 2iP resulted in greater adventitious shoot production and improved quality (nonvitrious) well formed shoots. Plants grown on in the greenhouse were of similar phenotypic habit regardless of the growth regulator used.