SOMATIC HYBRIDIZATION IN MINT - IDENTIFICATION AND CHARACTERIZATION OF MENTHA-PIPERITA (PLUS) MENTHA-SPICATA HYBRID PLANTS

Twenty eight somatic hybrid plants were identified following protoplas t fusions between peppermint (Mentha piperita L. cv Black Mitcham), pr oducing high-quality oil, and spearmint (Mentha spicata L. cv Native S pearmint), likewise producing high-quality oil and also possessing res istance to verticillium wilt. Prior to fusion, peppermint protoplasts were subjected to iodoacetic acid to inhibit cell division. Protoplast s of peppermint and spearmint were fused using polyethylene glycol plu s DMSO. Fusion products were cultured according to an efficient protop last-to-plant-cycle protocol developed for peppermint. Using this prot ocol, iodoacetic acid-treated peppermint protoplasts were not able to divide, whereas untreated spearmint protoplasts had the ability to pro duce callus but not shoots. Therefore, selection of somatic hybrid cal li was based on the presumed capability of hybrid cells to form calli and shoots. Shoots in vitro were initially identified as hybrids using RAPD profiles. Subsequently, observations on. morphology, chromosome counts, and Southern-hybridization patterns confirmed their hybrid sta tus. The results of verticillium tests revealed that 18 somatic hybrid s were more susceptible than Native Spearmint, while hybrid II-14 had a level of susceptibility intermediate between that of the fusion pare nts. Oil-analysis of hybrid plants indicated that they all have a GC-p rofile typical of spearmint oil.