Growth and root inhibition in Axenic hydrilla verticillata cultures
Cook, Rebecca Ann
Ward, C. H.
Master of Science
Hydrilla verticillata Royle is a submersed aquatic weed infesting waterways throughout the world. Hydrilla was introduced into the United States in 196 and has spread across the southern states. Hydrilla has extensive reproductive capacity, spreading by seeds, axillary and subterranean vegetative buds, fragmentation, and stolons. Subterranean buds, called tubers, are the predominant form of reproduction. This reproductive potential has made mechanical, chemical, and biological control largely ineffective. To study the life cycle of Hydrilla, Elaine and Ward (1981) developed a method for producing axenic cultures from tubers. The process by which axenic cultures were produced involves surface treatment of the tuber with sodium hypochlorite and removal of outer bud scales. Tubers were grown in a mineral salts media containing 15 ug/ml penicillin and 1 ug/ml streptomycin to prevent bacterial growth. Two percent glucose and .5 per cent casein were added to facilitate detection of bacterial contamination. Axenic cultures produced by this method have inhibited shoot and root growth. In the present study, different variables in the process were analyzed for inhibitory effects. Addition of yeast extract, IAA, IBA, GAg, and kinetin failed to overcome stem or root growth inhibition. Neither NaOCl treatment nor dissection as separate factors affected growth or root development. Sodium hypochlorite treatment followed by dissection resulted in retarded growth at times, although mature plants did develop. Addition of penicillin and streptomycin or penicillin, streptomycin, glucose, and casein resulted in inhibited growth and root production. Casein and streptomycin both inhibited stem and root growth in all cases. Glucose slightly enhanced growth. Penicillin had no significant effects on shoot growth or root formation and growth. Axenic cultures with penicillin and glucose exhibited no inhibitions. Streptomycin inhibits growth of roots at 15, 5, and 1 ug/ml. Penicillin did not affect growth of stems or roots at 25, 75, or 15 ug/ml but did not effectively control bacteria. Neomycin, ampicillin, tetracycline, and chloramphenicol were tested separately at 25, 75, and 15 ug/ml and in combinations at 75 ug/ml as possible alternatives to streptomycin. All were inhibitory to shoot growth. Root formation was significantly inhibited by all concentrations of chloramphenicol, and the higher concentrations of neomycin and tetracycline. Several of the antibiotic combinations, tested in conjunction with 25 ug/ml penicillin, were effective against bacteria but were inhibitory to hydrilla growth at tested concentrations.