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(TM) 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.