Garlic

CAVAGNARO, P. F., GALMARINI, C. R.

Genome Mapping and Molecular Breeding in Plants - Vegetables

Springer

Lugar: Heidelberg, Germany; Año: 2007; p. 349 - 361

[El trabajo no tiene Abstract (ver documento completo). En su lugar se adjunto la seccion "conclusiones"] The development of systems for the production of relatively large amount of seeds is a major accomplishment towards the domestication of this species. In fact, there is no evidence indicating that sexual reproduction and selection were ever used by garlic growers throughout history, thus, although garlic has been cultivated since ancient times, breeding the crop has just begun (Simon and Jenderek 2003). Breeding progress, in aspects related to the seed production system, has already been reported and future goals for garlic improvement are being considered. According to Simon and Jenderek (2003), garlic responds to selection for reduced numbers of small bulbils and, after a few seed-propagated generations, bulbil-free strains can be obtained in some genetic backgrounds. Likewise, they report improved pollen fertility in the first progeny derived from sexual reproduction. Marker assisted selection (MAS) for this trait is possible since molecular markers associated with pollen fertility have been identified (Etoh 1985; Hong et al. 1997, 2000b). Seeds vigor and size and seed germination rates can be dramatically improved after two or three cycles. Concerning the latter, Inaba et al. (1995) and Jenderek (1998) found that after two or three generations of selection for improved seed germination, germination rate increased from 10-35% to 65-93%. Simon and Jenderek (2003) indicate that seed yield can also be significantly improved and suggested that up to 1200 seeds can be produced per plant, if all the flowers in a garlic inflorescence set the maximum possible number of seeds.             With routine seed production underway, combining desired traits found in different garlic clones, is now feasible. Previously evaluated and characterized garlic collections, by means of morphological-, isozyme- and molecular markers, as well as regarding specific traits of interest (e.g., flavor, nutraceutical properties, resistance to pathogens) will provide a source of classified genetic variability, useful in the planning of garlic breeding programs. Among the breeding goals for this crop, besides those related to the improvement of the seed production system, are typical bulb traits, including clove number and color, bulb size and shape, color of outer and inner bulb scales, time of bulb maturity, yield and bulb storage parameters. Genetic resistance to viruses, fungi and nematodes are also very important breeding objectives.   Flavor and health-enhancing attributes are of particular interest for the consumer and the processing- and the nutraceutical industry.             According to Simon and Jenderek (2003), as garlic breeding proceeds, two different objectives can be pursued: development of new clones for asexual reproduction or development of seed-propagated cultivars. Although the latter is tempting since virus-free seed-propagated cultivars, and even hybrids, can be imagined, its likelihood of success is uncertain and, according to Simon and Jenderek (2003) it will likely be this way for several years. Instead, the development of new clones, by crossing plants with specific traits of interest, seems more feasible in the near future. By this means, a large number of recombinant phenotypes can be obtained, considering the broad diversity observed in garlic collections. If more gene markers and traits of agronomic importance are added to the linkage map of Ipek et al. (2005) and/or new more detailed maps are constructed, molecular markers linked to traits or genes of interest can assist with the selection process of garlic breeding programs.              Genetic transformation of selected garlic cultivars, with genes conferring specific traits of interest may create new phenotypes useful for different purposes of the grower, the consumer and the nutraceutical industry. For example, if the positive association between IVAA and pungency observed in garlic and onion is due to linkage, and not pleiotropy, transgene technology can be used to “break” this linkage, for developing mild (low pungency) varieties with high anti-platelet activity.