EMS and Transposon Mutagenesis for the Isolation of Apomictic Mutants in Plants

Apomixis is an asexual mode of reproduction through seed. It is widespread throughout the plant kingdom. Among angiosperms, more than 300 plant species from 35 different families have been described as apomictic. Apomixis is most common in Gramineae, Compositae and Rosaceae (Rutishauser, 1967; Nygren, 1967; Bashaw, 1980; Nogler, 1984; Hanna and Bashaw, 1987; Asker and Jerling, 1992; Hanna, 1991, 1995a,b; Koltunow, 1993; Khush et al., 1994). Apomixis is strongly correlated to polyploidy and hybridization, and it is more prevalent in the polyploid wild species. It is also widespread in several forage grasses, such as Cenchrus, Eragrostis, Paspalum, Poa and others, most of which are polyploid. Apomixis offers various benefits for crop improvement: 1. Apomixis allows vegetative reproduction through the seed, and thus can have a major impact not only in seed-propagated crops (cereals, vegetables), but also in vegetatively-propagated crops (e.g. potato). 2. A major advantage of apomixis is in F1 hybrid development for commercial seed production. It simplifies seed production, because isolation is not necessary, and there is no need to maintain or multiply parental lines. As an alternative to current commercial hybrid production systems, it would make hybrids readily available and affordable, reducing the costs of seed production. Thus, hybrid vigour can be exploited advantageously in vegetables, wheat, soyabean, rice, minor grains, forage and turf species, if apomixis genes could be introduced into the target crops. 3. Apomixis makes it possible to fix the genotype of a superior variety bred for a particular environment, so that clonal seeds can be produced continuously and economically. 4. Progeny testing for genetic stability is not needed for obligate apomixis, since any superior apomictic lines are ready for immediate performance evaluation.