Abstract
The clonal propagation of crops offers several advantages to growers, such as skipping the juvenile phase, faster growth, and reduced mortality. However, it is not known if the wild ancestors of most clonal crops have a similar ability to reproduce clonally. Therefore, it is unclear whether clonality was an ancestral condition, or if it evolved during domestication in the majority of these crops. Here, I assessed some traits that are relevant to clonal propagation using stem cuttings from chaya (Cnidoscolus aconitifolius) and compared these traits to those of its wild ancestor. Chaya is highly relevant crop to food security in its domestication center (Yucatan Peninsula) and is now cultivated in several countries. Chaya is also an excellent model for assessing the effect of domestication on clonality because wild relatives and selection targets are known. Specifically, I compared resistance to desiccation, water and resource storage, as well as the production of new organs (shoots and leaves) by the stems of wild and domesticated plants. I also compared their performance in root development and clone survival. I found that, relative to their wild ancestors, the stem cuttings of domesticated chaya had 1.1 times greater storage capacity for water and starch. Additionally, the stems of domesticated plants produced 1.25 times more roots, 2.69 times more shoots and 1.94 more leaves, and their clones lived 1.87 times longer than their wild relatives. In conclusion, the results suggest that artificial selection has optimized water and starch storage by stems in chaya. Because these traits also confer greater fitness (i.e. increased fecundity and survival of clones), they can be considered adaptations to clonal propagation in the agroecosystems where this crop is cultivated.
Highlights
The clonal propagation of crops offers several advantages to growers, such as skipping the juvenile phase, faster growth, and reduced mortality
The cultivar clones had greater survivorship than did their wild relatives when grown in a common garden
Observed differences in the traits of stems of wild and domesticated plants and in their performance when used as propagules were likely the result of artificial selection, consciously and unconsciously carried out by humans during the domestication of chaya
Summary
The clonal propagation of crops offers several advantages to growers, such as skipping the juvenile phase, faster growth, and reduced mortality. The results suggest that artificial selection has optimized water and starch storage by stems in chaya Because these traits confer greater fitness (i.e. increased fecundity and survival of clones), they can be considered adaptations to clonal propagation in the agroecosystems where this crop is cultivated. Because clonal propagation has brought several advantages to growers relative to sexual propagation (i.e. easier cultivation, greater survival and reduced time to reach sexual maturity)[9] and some of the few clonal crops studied so far have wild ancestors that mainly reproduced sexually[12,13], it is reasonable to think that clonality may be a derived trait in some crops and that traits that facilitate clonal propagation have been artificially selected during the domestication p rocess[9]. If the traits exhibited by the vegetative organs that were selected by growers affect their performance as propagules, this function is expected to be optimized by artificial s election[20,22]
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