Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 334

Bananas and plantains (Musa spp.) are perennial crops with rapid growth rate. They belong to the family Musaceae and are cultivated all year round in the tropics and sub‐tropics. Considered to be the favorite fruit crops of the world, they also are globally distributed in more than 120 countries, with a total production of approximately 106–140 million tonnes per year (Molina and Kudagamage 2002; FAOSTAT 2014). Bananas and plantains are the highest export fruit crops (FAO 2011) and are ranked fourth‐most important in sub‐Saharan Africa (SSA) after other vital crops including cassava, maize, and yam (FAO 2009). They are rich sources of carbohydrates, vitamin C, potassium, and sodium (International Banana Association 2007) in addition to their abundant uses in medicines, industrial raw materials, and other domestic applications (Abiodun‐Solanke and Falade 2010). The different ploidy constitutions of Musa species were derived from Musa acuminata (AA) and Musa balbisiana (BB) and are categorized into different groups including diploids (AA, AB, and BB), triploids (AAA, AAB, ABB, and BBB), and tetraploids (AAAA AAAB, AABB, and ABBB) (INIBAP 2003; Pollefeys et al. 2004). Also, East African bananas (mainly dessert types) (AA, AAB, AAA, ABB, and AB), and the African plantains (AAB) are grown mainly in Central and West Africa, while the East African Highland Banana (AAA), are for cooking and beer brewing (Karamura et al. 1998). Variations are evident in the phenotypic expressions of different ploidy constitutions including triploid plantain (ABB), diploid banana (AA), and triploid banana (AAA) (Figure B7.1) (IITA 2018). Phenotypically, plantains are known to be taller than banana trees (Figure B7.2). Bananas, especially the dessert ones (M. Cavendish, AAA) have thinner fleshy texture, and when in ripened form, more compact fruits than those of plantains, and change to yellow color (Figure B7.3). They contain sugar, have a sweeter taste, and are usually consumed raw. Plantains on the other hand, have thicker, fleshy skin due to high starchy composition, and turn yellow first and then black when ripened. In addition, plantain fruits have rough surfaces and more vitamins A and C and potassium, and can be cooked before consumption unlike banana fruits (Valmayor et al. 2000). The identified cultivated banana and plantain fruits vary with wild relatives by exhibiting seedless condition and parthenocarpy (development of fruit without seed or pollination and fertilization).

Figure B7.1 Variations in phenotypic expressions of different ploidy constitutions of plantain and banana fruits. (a) = triploid plantain (ABB); (b) = diploid banana (AA); (c) = triploid banana (AAA) (IITA+banana&fr = tightropetb&imgurl=http%3A%2F).

Figure B7.2 Different accessions of banana and plantain being maintained in the greenhouse at Natural Science Department, Bowie State University: (a) = plantain (Poteau Geant, ABB); (b) = Plantain (Pata, ABB); (c) = banana (Gros Michel, AAA); and (d) = plantain (Balonkawe, ABB).

Source: Picture – Natural Science Department Greenhouse, Bowie State University.

Figure B7.3 Phenotypic comparison of plantains and bananas in their fruits form. (a) = bunch of Agbagba plantain fruits on plantain tree; (b) = bunch of plantain hybrid PITA 2 with fruits; and (c) = bunch of banana fruits (IITA+banana&fr = tightropetb&imgurl = http%3A%2F).

Production of these vital crops is challenged by pathogenic and abiotic factors. With rising global temperatures, which are expected to have drastic effects including altered patterns of drought, salinity, emergence of new pests, and diseases, plant growth and yield will be adversely impacted (Tester and Langridge 2010). Using informative molecular markers for assessment of genetic diversity to harness allelic richness, and selecting those with unique and desired traits for rapid production, maintenance, and germplasm conservation via plant tissue culture techniques, would be the right combination of tools to obtain favorable genotypes and to ensure periodic availability of good planting materials for farmers. This is vital since the world population is growing fast and is expected to reach over 9 billion by the year 2050 (FAO 2015). Feeding this overwhelming population level is generating much pressure on agricultural crop production (Dempewolf et al. 2014; Khoury et al. 2014).