Screening of aqueous extracts from gelling agents (Agar and Gelrite) for root-stimulating activity

A dilution series of water extracts made from 13 gelling agents commonly used in tissue culture was screened for root-stimulating activity using the mungbean bioassay. The gelling agents were grouped according to their rooting response as good (30 roots or more per cutting), intermediate (20–30 roots per cutting) or poor (less than 20 roots per cutting). The best rooting response, comparable to rooting with exogenously applied IBA at 10− 3 M, was detected in extracts from Agar Bacteriological, Difco Bacto Agar, Difco BiTek™ Agar and Malt Extract Agar. Malt Extract Broth and Mueller- Hinton Agar extracts inhibited rooting when applied at high dilutions (100% and/or 50%). Extraction of Gelrite with water was problematic and a poor rooting response was observed. Four gelling agents (Difco Bacto Agar, Agar Commercial Gel, Agar Bacteriological and Gelrite) were further investigated. Compounds which co-chromatographed with authentic IAA after HPLC separation were detected in all four of these gelling agents.