From Wild Species to Landraces and Cultivars
Patrick Byrne, Dept. of Soil and Crop Sciences, Colorado State University, Fort Collins, Colorado 80523<EMAIL_ADDRESS>Christopher Richards, USDA-ARS National Laboratory for Genetic Resources Preservation, 1111 S. Mason St., Fort Collins, Colorado, 80521
Gayle M. Volk, USDA-ARS National Laboratory for Genetic Resources Preservation, 1111 S. Mason St., Fort Collins, Colorado, 80521
Outline
1. Introduction
The wild relatives of domesticated plant species usually do not possess all the desirable traits for routine agricultural production and use. This chapter offers an overview of the process of early crop domestication from thousands of years ago through to the progress in plant improvement by modern-day plant breeders. 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.
2. Early crop domestication
One of the landmarks of human history is the transition from nomadic hunter-gatherer societies to settled agriculture-based societies, the so-called neolithic revolution. A key component of this transition was the domestication of wild species into cultivated crops capable of supporting higher population densities (Harlan, 1992; Schwanitz, 1966). Crop domestication from wild species began about 8000 to 10,000 years ago independently in many parts of the world. 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).
Early farmers selected for traits either deliberately or unintentionally that made the wild plants more suitable for human needs (Figure 1). These included characteristics that improved yield (more or bigger harvested product; reduced branching), made agricultural production easier (loss of seed dormancy; retention of seed on the plant), or improved product quality (reduced bitterness or toxic properties; easier processing). The term ‘domestication syndrome’ has been used to encompass the collection of traits that were commonly selected (Gepts, 2018).
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.
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 (Gepts, 2018). Domestication most like