Establishment and characterization of Rubus tissue culture systems for in vitro bioassays against phytotoxins from Rubus fungal pathogens

The Rubus species R. parviflorus, R. spectabilis and R. strigosus interfere with conifer seedling establishment on forest regeneration sites in Canada and the United States. As a first step towards microbial metabolite-based control, callus and cell suspension cultures of the Rubus species were deve loped as a bioassay system to detect phytotoxic compounds that may have rel evance in a vegetation control context. Rapidly growing friable callus and suspension cultures were obtained from leaf disks of the three weedy Rubus species using similar culture media conditions (modified Murashige and Skoo g) but required different plant growth regulators (R. parviflorus, 4.5 muM 2,4-D; R. spectabilis, 26.9 muM NAA/0.5 muM zeatin; and R. strigosus, 12.4 muM picloram). Cell growth and health attributes including callus circumfer ence, degree of browning and suspension culture cell viability as measured by the TTC vital stain assay were developed and were rapid and convenient t o use. We have established Rubus tissue culture systems that will make it p ossible for large scale screening of phytotoxic metabolites.