اصلاح ژنتیکی موز با استفاده از تکنولوژی های آزمایشگاهی

ABSTRACT Genetic Improvement of Banana Using Conventional and In Vitro Technologies

Banana (Musa spp.) is an evergreen perennial, monocotyledonous plant of the family Musaceae. The latter consists of seminiferous and cultivated species with broad biological diversity (Abadie et al. 2003). Currently, about 1,000 banana cultivars and landraces are recognized from 50 or so Musa species (Heslop-Harrison & Schwarzacher 2007). Bananas are grown in the tropics and subtropics at latitudes of 20 degrees above and below the equator, where there is a wide seasonal variation in rainfall and temperature (Pua 2007).

Two wild species, M. acuminata and M. balbisiana, are the progenitors of modern edible bananas. The main centers of diversity for M. acuminata and its derivative hybrids are Malaysia and Indonesia (Asif, Mak, & Othman 2001; Daniells et al. 2001), whereas M. balbisiana and its hybrids are presumed to be native to India (Robinson 1996). The distribution of bananas from their centers of origin is probably through planting of vegetative materials transported to other tropical and subtropical regions, such as Africa, the Caribbean, Latin America, Oceania, and the Middle East (Price 1995; Robinson 1996). Banana plants were introduced about 500 years ago into Central and Latin America, where the crop became of major economic importance (van den Houwe, Panis, & Swennen 2000). Distinct centers of secondary genetic diversification may have evolved in the Great Lakes region of East Africa and in the more humid forests of Central and West Africa (van den Houwe, Panis, & Swennen 2000). Currently, bananas are cultivated in 120 countries throughout the humid tropics and subtropics in the Americas, Asia, Africa, Australia (Queensland), and Europe (Canary Islands) (Heslop-Harrison & Schwarzacher 2007). The leading producers of bananas in 2007 were India, China, The Philippines, Brazil, and Ecuador (FAOSTAT 2009).

Bananas are multipurpose plants because most of their parts can be used in various ways, depending on the species. The most important part is the edible fruit, which can be eaten either ripe as a dessert, or unripe as boiled, fried or roasted food (Smith et al. 2005). Nutritionally, the fruit is rich in carbohydrates, vitamins A, B, and C, and potassium (Aurore, Parfait, & Fahrasmane 2009). The unripe fruit can be brewed to form beer and wine, or processed into sauce, flour, chips, crisps, smoked products, and confectionary. Unripe fruit is also a source of amylase and starch (van den Houwe, Panis, & Swennen 2000). Male floral buds can be eaten as a boiled vegetable, whereas pseudostems are a source of fiber for the manufacture of rope, paper, and textiles. Banana leaves are used for thatching, in the production of fabric and cordage, and as mulch and animal forage (Smith et al. 2005). Species such as M. ornata and M. velutina are popular ornamental plants (Heslop-Harrison & Schwarzacher 2007).

Banana cultivation is focused mainly on parthenocarpic cultivars for the production of edible fleshy seedless fruit, an important food on a global scale. The world banana-fruit production in 2007 was estimated to be 86 million tons, harvested from an area of about 5 million hectares. In developing countries, bananas are the fourth most important crop after rice, wheat, and maize in production. Banana ranked second after citrus on the basis of the world fruit-crop production in 2007 (FAOSTAT 2009). Approximately 47% of the global banana-fruit production has been dominated by cultivars of the Cavendish type because of their high yields and short periods to maturity (Robinson 1996; Kulkarni et al. 2007). The leading producers of banana fruit in 2007 were India, China, the Philippines, Brazil, and Ecuador. Globally, the production of bananas is primarily for local consumption as a dietary supplement or staple food in the producing countries. An estimated 80% (68 million tons) of the world banana-fruit production in 2007 was consumed and traded locally in the producing countries. Banana fruit, essentially of the cooking type, is important as a staple food in the East African highlands. Consequently, fruit production is important to both food and income securities of the producing countries.

Bananas are popular as fresh fruit in temperate countries. In 2007, the world export of bananas, consisting mainly of Cavendish-type dessert bananas, was estimated to be 18 million tons (20% of world production), amounting to US$7.2 billion in economic terms (FAOSTAT 2009). The most important attributes that make the Cavendish subgroup the main bananas for export are related to their reliability during transport and their shelf life, rather than taste. In economic value, banana fruit ranked fifth in the world trade for agricultural crops (Aurore, Parfait, & Fahrasmane 2009), the leading banana exporters in 2007 being Colombia, Costa Rica, Ecuador, Guatemala, and the Philippines. The leading importers were Belgium, Germany, the United Kingdom (UK), and the United States.

Sexual hybridization and mutation have produced numerous banana varieties with different ploidy and genome combinations. Bananas are classified according to their ploidy, based on the number of sets of chromosomes, namely diploid (2n = 2x = 22), triploid (2n = 3x = 33), and tetraploid (2n = 4x = 44). The majority of cultivars are triploids, some are diploids and seedless, but very few are tetraploids. Bananas are also classified into genomic groups based on their genome constitutions, which are designated by the letters A, B, S, and T to represent M. acuminata (AA), M. balbisiana (BB), M. schizocarpa (SS), and M. textilis (TT), respectively. Additionally, they are classified into several main subgroups, including Sucrier, Gros Michel, Bluggoe, Ice Cream, Mysore, and Cavendish. The Cavendish subgroup is divided into Dwarf Cavendish, Giant Cavendish, Pisang Masak Hijau, Robusta, and Valery. Most commercial banana cultivars, with triploid AAA genomes, belong to the Cavendish subgroup (Robinson 1996).