Characteristics of wild and domesticated spp

Wild and domesticated spp

1. Characteristic of wild and domesticated spp

2. 1. INTRODUCTION The wild relatives of domesticated plant species usually do not possess all the desirable traits for routine agricultural production and use. An understanding of crop domestication and plant breeding provides a context for the value, importance, and use of crop wild relatives that are conserved either  in situ  or in genebanks .

3. Domestication Domestication is an evolutionary process of genetic development, in which natural selection is replaced by human selection shaping crop plants for specific needs . It is estimated that 230 crops have been domesticated, belonging to 180 genera and 64 families. Some families, such as Gramineae ( Poaceae ), Leguminoseae (Fabaceae), Cruciferae, and Solanaceae, have yielded more domesticates than others. Wild plant  means any undomesticated species,

4. Periods of domestication Crop domestication from wild species began about 8000 to 10,000 years ago independently in many parts of the world. Four general periods of domestication were proposed by N. W. Simmonds as: ( i ) ancient (7000–5000 bc ); (ii) early (5000–0 bc ); (iii) late ( ad 0–1750); and (iv) recent (after ad 1750).

5. Centers of Domestication Some of the more notable centers of domestication were; The Fertile Crescent of the Middle East (wheat, barley, lentil, and chickpea), Mesoamerica (maize or corn, chiles, squash, and common bean), The Andean region (potato, tomato, and a second center of origin for common bean) , and Southeast Asia (rice, millet, and soybean).

6. DOMESTICATION of wheat The domestication of wild species was accelerated by the early practice of harvesting mutant plants with useful traits. A good example is cultivated wheat as it descended from wild ancestors that differed markedly from modem cultivars. The seed­bearing spikes of the primitive wheats were brittle and easily broken apart, causing seeds to shatter and fall to the soil surface as they ripened. Seeds were covered with hulls that adhered tightly and were difficult to remove before seeds could be eaten. Over long periods of time, perhaps 5,000 to 10,000 years, mutant forms of wheat gradually emerged in which seeds were held firmly until harvest, yet could be separated cleanly from the hulls. These new forms of wheat were gathered as they were easier to harvest and to prepare for food. Eventually, they became the wheats cultivated by prehistoric people.

7. Changes accompanying domestication Typical changes occurring during the development from a wild plant to a domesticated crop are referred to as the domestication syndrome; they include; the loss of seed dormancy, increased rates of self-pollination, adoption of vegetative propagation, increase in yield of seed or other plant organs utilized, compact growth habit, loss of seed dispersal, increase in number and size of seeds and inflorescences, changes in color, taste and texture, and decrease in the content of toxic substances. Although the exact composition of the domestication syndrome traits depends on the particular species, certain basic characteristics are common (Table 2.1.).

8. Figure 1.  Comparison of seeds of wild progenitor species (left) and their domesticated counterparts (right). Note change in seed size, as well as reduced pigmentation in some cases. From top to bottom: pistachio, coffee, soybean, barley, North American wild rice (Zizania palustris), and sorghum. Photo credit: Christina Walters.

9. Genetic Basis of Domestication Traits Many of the domestication traits are characterized by simple inheritance, i.e., they are controlled by one or two genes with large effects rather than by multiple genes. The simple inheritance of domestication traits would have facilitated their selection and incorporation into wild populations. Domestication most likely occurred over an extended period of time, with ongoing cross-pollination between wild and domesticated populations. Because the selected plants represented just a small fraction of the total wild population, domestication was often accompanied by a reduction of genetic diversity .

10. Domestication and Genetic Diversity As early farmers migrated into new territories, they brought their seeds, tubers, and rootstocks with them. The crops would have encountered a variety of soil types, weather patterns, insect pests, and pathogens. In response to the new environments, farmers would have selected for plants that were better adapted to the local conditions. Thus arose ‘ landraces’, traditional varieties selected by farmers for adaptation to local conditions and food preferences. These varieties typically have low yield potential, but are often genetically diverse and stress-resilient. Many so-called ‘heirloom varieties’ are examples of landraces. Typically landraces are genetically heterogeneous (non-uniform), and are therefore an important source of genetic diversity for crop improvement. Landraces are usually less diverse than their wild ancestors, but more diverse than cultivars produced during the modern era of plant breeding.

11. Conceptual representation of a reduction in genetic diversity (the bottleneck effect) as wild species were domesticated, and a further reduction that occurred with development of modern cultivars. Colors represent the diversity of alleles within a population. Rather than abrupt changes as indicated by the pronounced bottlenecks here, domestication and crop improvement are now viewed as leading to a gradual loss of diversity over a long period of time.

12. Reduction of genetic diversity during evolution of common bean (Phaseolus vulgaris) in the Andean and Meso-American centers of origin. 

13. Characters of wild and domesticated species Wild Species High in genetic diversity Highly resistant against biotic and abiotic stresses Wide adaptability Quantitative inheritance Domesticated Species Low in genetic diversity Less resistant against biotic and abiotic stresses Low adaptability Qualitative inheritance

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