TRUE SEEDS IN GARLIC
Scientists believe that wild relatives of garlic were widely dispersed in Central Asia about 10,000 years ago. Semi-nomadic tribes cultivated this plant as food condiment and medicinal plants. From Central Asia garlic was introduced to the Mediterranean basin, India and China. There is evidence that garlic has been in use in China and India for more than 5,000 years and in Egypt since before 2,000 BCE. European traders facilitated its further distribution, and, from the Mediterranean region, garlic was introduced to sub-Saharan Africa and to the Americas by explorers and colonists. Today garlic is known only as a cultivated plant, and its wild relatives are not found.
During its cultivation history in different regions, garlic was adapted to various climates and selected for cold resistance, bigger bulbs, or higher pungency. In order to obtain a larger bulb, flower stalks were often removed or clones with reduced flowering potential were selected. Thus, the thousands of years of active selection by man resulted in the loss of garlic fertility, and today garlic varieties are completely sterile, they don't produce seeds and are propagated only vegetatively. In modern garlic varieties, the presence of vegetative topsets (bulblets), which develop in garlic inflorescence, is one of the major causes of the inability of this plant to develop normal flowers and true seeds.
The sexual sterility of garlic markedly reduces its potential for the improvement of its economically important traits, including pest resistance, yield, and quality. Restoring fertility in this crop would provide new genetic combinations for breeding purposes or genetic studies. This consideration has stimulated attempts by many researchers to restore fertility to garlic.
In the early 1980s, Japanese researcher Prof. Takeomi Etoh made several expeditions to Soviet Central Asia, and collected a number of garlic bulbs. The collected clones were then grown in Kagoshima, Japan, and following topset removal, 17 clones developed fertile flowers with over 3,000 viable seeds. However, seed germination rates were low, ranging between 10 and 12%. Later, in the 1990’s, Maria Jenderek obtained in California a large amount of garlic seeds from the plants originated in Central Asia. Removal of topsets was necessary only in the early generations, as the strong selection pressure for blooming and seed production resulted in improved seed set. Fertile accessions were also identified in the USA garlic collections.
In 1998, a special project for restoring the fertility of garlic was initiated in Israel by
Prof. Rina Kamenetsky (The Volcani Center) and
Prof. Haim D. Rabinowitch (The Hebrew University of Jerusalem). In the framework of this project, our collection missions to Central Asia have gathered over 300 garlic genotypes from locally cultivated or natural populations in Uzbekistan, Tadjikistan, Kirgizistan, and Kazakhstan. This region is recognized as the primary centre of origin of garlic and the main and richest source for genetic diversity, worldwide. The collected clones were evaluated in Israel for their potential fertility and other useful traits.
It was found that following stalk elongation, flower differentiation, pollination, and fertilization, true garlic seeds might be obtained in more than 30 clones. In seven of the most fertile accessions, about 400-500 seeds were produced per umbel, without the removal of topsets. Germination rates reached about 90%, and the seedlings developed into young plants with two to five leaves. At the end of the season, single-clove bulbs with white, purple, gray and brown skins, differing in bulbing ability and ripening, were obtained. These plants vary widely in their physiological and horticultural characteristics, and probably contain most of the worldwide variability of the garlic genepool.
Seed propagation of garlic on a massive scale may become a feasible option in the future. Sexual reproduction can be exploited in plant breeding, for improvements to yield, tolerance to biotic and abiotic stresses and quality. In addition, in established varieties, seeds (which normally do not transmit viruses) may be used for the production of virus-free propagation material.
References:
Kamenetsky, R. and H. D. Rabinowitch (2001) Floral development in bolting garlic. Sexual Plant Reproduction, 4, 235-241.
Kamenetsky, R. London Shafir, I., Zemah, H., Barzilay, A. and. Rabinowitch H. D. 2004. Environmental Control of Garlic Growth and Florogenesis. Journal of the American Society for Horticultural Science, 129: 144-151
Kamenetsky, R., London Shafir, I., Baizerman, M., Khassanov, F., Kik, C. and H.D. Rabinowitch (2003)
Garlic (Allium sativum L.) and its wild relatives from Central Asia: evaluation for fertility potential. ,
Acta Hort. 637:83-91
Kamenetsky, R., London Shafir, I., Khassanov, F., Kik, C., van Heusden, A.W., Vrielink-van Ginkel, M., Burger- Meijer, K., Auger, J., Arnault, I. and Rabinowitch, H.D (2005) Diversity in fertility potential and organo-sulphur compounds among garlics from Central Asia.
Biodiversity and Conservation. 14:281-295
Kamenetsky, R. London Shafir, I., Zemah, H., Barzilay, A. and. Rabinowitch H. D. (2004) Environmental Control of Garlic Growth and Florogenesis. Journal of the American Society for Horticultural Science, 129: 144-151
Kamenetsky, R. (2007) Garlic: Botany and Horticulture. Horticultural Reviews, Vol 33, 123-172
Rotem, N., Shemesh, E., Peretz, Y., Akad, F., Edelbaum, O., Rabinowitch, H.D., Sela, I. and R. Kamenetsky (2007). Reproductive development and phenotypic differences in garlic are associated with expression and splicing of LEAFY homologue gaLFY. Journal of Experimental Botany, Vol.58, No.5, pp. 1133 –1141
Kamenetsky, R., Khassanov, F, Rabinowitch ,H.D., Auger J., and Kik C. (2007) Garlic Biodiversity and Genetic Resources. Medicinal and Aromatic Plant Science and Biotechnology, Global Science Books , p. 1-5
Zheng, S-J., Kamenetsky, R., Féréol, L., Barandiaran, X., Rabinowitch, H. D, Chovelon, V. and Kik C. (2007) Garlic Breeding System Innovations Medicinal and Aromatic Plant Science and Biotechnolog, Global Science Books, p. 6-15