The effect of dinitroaniline and phosphorothioamidate herbicides on polyploidisation in vitro of Nepeta plants.

Abstract

Experiments on polyploidisation of plants began in 1940, when colchicine was found to double the chromosome activity in higher plants cells (Hancock, 1997). By 1979, the chromosome numbers of well over 150 plant species had been doubled using colchicine (Dewey, 1979). Unfortunately, amid all this promise, small numbers of polyploidised crops were ever released and few ever dominated the world market (Hancock, 1997). Colchicine has a strong toxic effect on plant cells: it inhibits the proliferation and regeneration of plants and induces chimerical plant forms. This is the main reason for testing such compounds as phosphorothioamidates and dinitroanilines as potential polyploidising agents. They have a similar mode of anti-microtubular activity as colchicine, but are sometimes less toxic because they possess a highly specific binding affinity to plant tubulins and promote effective microtubule depolymerisation at low concentrations (Morejohn and Fosket, 1991). Agents such as amiprophos-methyl (APM), oryzalin, and trifluralin have been used for polyploidisation of higher plants (Chalak and Legave, 1996; Salon and Earle, 1998; Sree Ramulu et al., 1991; Tosca et al., 1995; Zhao and Simmonds, 1995). In this paper we report for the first time the comparative polyploidising effects of colchicine, APM, and a wide spectrum of different dinitroanilines (oryzalin, ethalfluralin, trifluralin, pendimethalin, and benefin), which have been assessed for production of new polyploid forms of Nepeta sp. Some species of nep are prospective medicinal, essential-oil, spicy-aromatic, and ornamental cultures. The use of polyploidy in breeding of nep species is a potential method for elevating the productivity of secondary metabolism, the development of ornamental characteristics, and (in interspecific hybridisation) the restoration of F1-sterility at the tetraploid level.