Streptomycin and Other Inhibitors as Selection Agents in Corn Tissue Cultures 1

We were interested in developing a tissue culture selection system to use in identifying potential extranuclear genetic markers in corn ( Zea mays L.). Streptomycin, kanamycin, chloramphenicol, aurin tricarboxylic acid, rifampicin, and erythromycin were evaluated for inhibition of seedling root growth and nonregenerable callus cultures of the inbred A619(N). All compounds caused inhibition at one or more concentrations in one or both bioassays. In additional tests on established, regenerable tissue cultures of the inbred A188(T), streptomycin and kanamycin inhibited growth at 100 μmol L −1 but not 10 μmol L −1 , while chloramphenicol was inhibitory at 10 μmol L −1 . Although all six compounds probably could be used as inhibitors in a tissue culture selection system, streptomycin, kanamycin, and chloramphenicol were the most inhibitory and appeared to be the most feasible to use. A188(T) and A188(N) regenerable tissue cultures were exposed to various levels of streptomycin for eight or five culture periods (cycles of selection), respectively. Culture growth was not inhibited at 50 μmol L −1 or less streptomycin, but was at 75 and 100 μmol L −1 . Three cycles of selection (40 days each) on 75 or 100 μmol L −1 were required for the cultures to lose all green pigmentation, after which selection for streptomycin resistance could be based on reappearance of green tissues. A culture sector that exhibited green tissues and a faster growth rate was identified after five cycles of selection on 100 μmol L −1 streptomycin. Six plantlets were regenerated from this source, but none developed past the third leaf stage so mature plant tests and progeny were not obtained to verify the resistance of this potentially variant culture line.