Mentha species: In vitro regeneration and genetic transformation

Mentha is a genus of aromatic perennial herbs belonging to the family Lamiaceae. It is distributed mostly in the temperate and sub-temperate regions of the world. Several Mentha species are considered industrial crops as they are a source of essential oils enriched in certain monoterpenes, widely used in food, flavour, cosmetic and pharmaceutical industries. Mentha has a large number of species that differ widely in their characteristics and polyploidy level. It is known to comprise about forty recognizable species. Utilizing crosses between Mentha species, it has been shown that single Mendelian gene(s) control the presence or absence of major compounds such as carvone, menthone, menthol and piperitone. The monogenic basis for conversion of menthone to menthol showed that gene R, either homozygous (RR) or heterozygous (Rr), is responsible for the reduction of menthone to menthol or carvone to carveol. Enzymes involved in monoterpene biosynthesis are described. Pests and pathogens of Mentha that cause substantial damage to the crop and considerable loss in oil yield are also described. Termites, cutworms, whitefly and semiloopers damage different parts of the Mentha plant. A number of microbes, viz. Macrophomia phaseoli and Puccinia menthae, also damage the Mentha plant. Control measures such as the use of insecticides, disease-inhibiting chemicals, and breeding of pest and pathogen resistant plants are reviewed. Agrobacterium genes responsible for the transfer of DNA, and selectable marker genes are discussed. Plant transformation technology has not only played an important role in introducing insecticidal genes into relevant crops but also has become a versatile platform for cultivar improvement as well as for studying gene function in plants