Were Fertile Crescent crop progenitors higher yielding than other wild species that were never domesticated?

Abstract

During the origin of agriculture in the Fertile Crescent, the broad spectrum of wild plant species exploited by hunter-gatherers narrowed dramatically. The mechanisms responsible for this specialization and the associated domestication of plants are intensely debated. We investigated why some species were domesticated rather than others, and which traits they shared. We tested whether the progenitors of cereal and pulse crops, grown individually, produced a higher yield and less chaff than other wild grasses and legumes, thereby maximizing the return per seed planted and minimizing processing time. We compared harvest traits of species originating from the Fertile Crescent, including those for which there is archaeological evidence of deliberate collection. Unexpectedly, wild crop progenitors in both families had neither higher grain yield nor, in grasses, less chaff, although they did have larger seeds. Moreover, small-seeded grasses actually returned a higher yield relative to the mass of seeds sown. However, cereal progenitors had threefold fewer seeds per plant, representing a major difference in how seeds are packaged on plants. These data suggest that there was no intrinsic yield advantage to adopting large-seeded progenitor species as crops. Explaining why Neolithic agriculture was founded on these species, therefore, remains an important unresolved challenge.

Keywords: Fertile Crescent; crop progenitors; domestication; harvest traits; origins of agriculture; seed size; yield.

Figure 1

The mass of individual seeds sown for grass species, shown as the log_e of seed mass (mg). Data are shown in categories of domestication status (confirmed founder crop progenitors, putative crop progenitors and other wild species) in descending order of individual seed mass. Species are Hordeum vulgare ssp. spontaneum, Triticum turgidum ssp. dicoccoides, Triticum monococcum ssp. aegilopoides, Triticum araraticum, Secale vavilovii, Triticum urartu, Avena sterilis, Avena fatua, Aegilops tauschii, Aegilops speltoides, Aegilops crassa, Secale strictum, Taeniatherum caput‐medusae, Hordeum murinum ssp. glaucum, Eremopyrum distans, Bromus tectorum, Hordeum marinum ssp. gussoneanum, Eremopyrum orientale, Bromus brachystachys, Eremopyrum bonaepartis, Lolium rigidum, Phalaris minor, Phalaris paradoxa and Stipa capensis. Error bars show ± 1 SEM. Crop progenitors have larger seed mass both when the conservative list of confirmed progenitors is used (F _1,22 = 7.0, P < 0.05) and when the putative progenitors are included (F _1,22 = 43.8, P < 0.001).

Figure 2

The mass of individual seeds sown for legume species, shown as the log_e of seed mass (mg). Data are shown in categories of domestication status (crop progenitors and other wild species) in descending order of individual seed mass. Species are Cicer reticulatum, Pisum sativum ssp. elatius var. pumilio, P. sativum ssp. elatius, Vicia ervilia, Lens culinaris ssp. orientalis, Vicia narbonensis, Lupinus angustifolius, Lathyrus cicera, Pisum fulvum, Vicia peregrina, Lathyrus aphaca, Lathyrus inconspicuus, Cicer judaicum, Scorpiurus muricatus, Lens culinaris ssp. odemensis, Lens nigricans, Medicago polymorpha, Coronilla scorpioides and Melilotus indicus. Error bars show ± 1 SEM.

Figure 3

Total seed yield (g) of cereal crop progenitors and other wild grasses that were potentially gathered before the transition to agriculture. Crop progenitors are separated into confirmed and putative progenitors. Data shown are for all individuals (grey circles) and the species mean (black circles), and species are in descending order of individual seed mass at sowing within each group. Species are Hordeum vulgare ssp. spontaneum, Triticum turgidum ssp. dicoccoides, Triticum monococcum ssp. aegilopoides, Triticum araraticum, Secale vavilovii, Triticum urartu, Avena sterilis, Avena fatua, Aegilops tauschii, Aegilops speltoides, Aegilops crassa, Secale strictum, Taeniatherum caput‐medusae, Hordeum murinum ssp. glaucum, Eremopyrum distans, Bromus tectorum, Hordeum marinum ssp. gussoneanum, Eremopyrum orientale, Bromus brachystachys, Eremopyrum bonaepartis, Lolium rigidum, Phalaris minor, Phalaris paradoxa and Stipa capensis. There is no difference in total yield between the two groups of species.

Figure 4

Total seed yield (g) of pulse crop progenitors and other wild legumes that were potentially gathered before the transition to agriculture. Data shown are for all individuals (grey circles) and the species mean (black circles), and species are in descending order of individual seed mass at sowing within each group. Species are Cicer reticulatum, Pisum sativum ssp. elatius var. pumilio, P. sativum ssp. elatius, Vicia ervilia, Lens culinaris ssp. orientalis, Vicia narbonensis, Lupinus angustifolius, Lathyrus cicera, Pisum fulvum, Vicia peregrina, Lathyrus aphaca, Lathyrus inconspicuus, Cicer judaicum, Scorpiurus muricatus, Lens culinaris ssp. odemensis, Lens nigricans, Medicago polymorpha, Coronilla scorpioides, Melilotus indicus. There is no difference in total yield between the two groups of species.

Figure 5

Chaff of grasses, shown as a percentage of the total grain and chaff mass. Crop progenitors are separated into confirmed and putative progenitors. Data shown are for all individuals (grey circles) and the species mean (black circles), and species are in order of descending order of individual seed mass at sowing within each group. Species are Hordeum vulgare ssp. spontaneum, Triticum turgidum ssp. dicoccoides, Triticum monococcum ssp. aegilopoides, Secale vavilovii, Avena sterilis, Avena fatua, Aegilops tauschii, Aegilops speltoides, Secale strictum, Taeniatherum caput‐medusae, Hordeum marinum ssp. gussoneanum, Eremopyrum orientale, Bromus brachystachys, Eremopyrum bonaepartis, Phalaris paradoxa. There is no difference in allocation to chaff between the two groups of species.