Micropropagation of Prosopis Species (Mesquites)
The genus Prosopis (family Leguminosae) is composed of nearly 45 species, commonly called mesquites, distributed in arid and semiarid zones of Asia, Africa, Australia, and America. Forty-two of these species are native to America, where they are distribut
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1 Introduction 1.1 Botany, Distribution, and Importance of Prosopis Species
The genus Prosopis (family Leguminosae) is composed of nearly 45 species, commonly called mesquites, distributed in arid and semiarid zones of Asia, Africa, Australia, and America. Forty-two of these species are native to America, where they are distributed from western North America to Patagonia, with an important polymorphism center in central-west Argentina (De Ataide 1990). The species range from shrubs to large trees that may reach 20 m in height and 1 m in diameter. Wide phenotypic diversity in the morphology of leaves, fruits, and thorns, and in the growth rate, habit, and adaptability to extreme environmental conditions has been described. Most of the species have sharp, strong thorns, and leaves are deciduous bipinates, with two or four folioles (Burkart 1979). The flowers are small and yellow-green in color, and are arranged in fine cylindrical bunches or sometimes in globose form. The fruits are thick pods that may reach 30 cm in length in some species. They are either flattened or cylindrical, straight or bent, with a thin exocarpus, and are leathery to woody, and have a variety of colors, from white to red and from yellow to purple (Galindo and Garcia 1991). Inside, the pods have a sweet pulp around the seeds, which are light brown, oval, and flattened (Allen and Allen 1981). Prosopis species are selfincompatible, and natural hybridization has been described in many cases (Simpson 1977; Naranjo et al. 1984; Balboa et al. 1990); in many places they exist as interspecific complexes with natural hybrids. Mesquites have been proposed as an ideal species for reclamation of arid and semiarid zones, since they live in extreme climatic regions with high solar radiation, severe temperature oscillations, and scarce rain (NAS 1980; Felker 1984). In addition, they can grow in soils that are dry, poor in organic nutrients, and high in salt and lime (Arce et al. 1990). Prosopis species have an extended, deep radical system that tightens sandy soils, thereby preventing erosion, and their roots are associated with Rhizobium bacteria that fix nitrogen, recovering and conserving soils poor in this nutrient. The large trees of 'Facultad de Ciencias Biologicas, Pontificia Universidad Catolica de Chile, Casilla 114-D, Santiago, Chile Biotechnology in Agriculture and Forestry, Vol. 39 High-Tech and Micropropagation V (ed. by Y.P.S. Bajaj) © Springer-Verlag Berlin Heidelberg 1997
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J.P. J\rcc and M.e. Medina
this genus provide shade that is very important for animals and the growth of herbaceous plants in arid zones. For these reasons, many of the Prosopis species, i.e., P. alha, P. alpataco, P. chi/ensis, P. cineraria, P.farcta, P.flexuosa, P.julijfora, and P. tamaru~o, have been used in reforestation programs with the aim of halting desertification and improving soils in arid and semiarid regions around the world (Fig. la). South American and Mexican species have been introduced in the USA with excellent results in improvement of productivit
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