DETECTION AND ERADICATION OF ENDOPHYTIC BACTERIA FROM MICROPROPAGATEDMINT PLANTS

Liquid medium and an enriched agar were used to detect endophytic bact eria in micropropagated mints (Mentha spp.) within 2 to 6 d of inocula tion. Bacteria isolated from the cultures were screened on several ant ibiotic concentrations to determine bactericidal doses. Antibiotics we re also tested for phytotoxic effects. Shoot tips from infected plants were treated by immersion in liquid MS medium containing antibiotics either singly or in combination. Streptomycin applied at 1000 mu g/ml for a period of 10 d was effective and less phytotoxic in a larger num ber of cases than gentamicin (50 mu g/ml), neomycin (500 mu g/ml), or rifampicin (30 mu g/ml). Mint cultures that tested negative for bacter ia after antibiotic treatment were multiplied, retested, and cold-stor ed for 1 yr or longer. Upon regrowth after storage, 25 of 30 treated c ultures (83%) tested negative for bacteria. Of the 25, 8 were successf ully treated with streptomycin, 1 with gentamicin, 2 with neomycin, 1 with rifampicin, and 1 with streptomycin and gentamicin; 12 required m ore than one treatment. An early detection system, initial trial treat ment with streptomycin for infected plants, and monitoring of treated cultures successfully reduced the spread of bacterial contamination. A ntibiotic treatment in liquid MS medium at pH 6.9 resulted in enhanced bactericidal activity over that seen at pH 5.5.