Schriften zu Genetischen Ressourcen - Genres

Unconscious selection in plants under domestication
effective devices have evolved to ensure this function. Under the system of sowing
and reaping, the grower collects and casts the seeds. Consequently, the wild-type
seed dispersal apparatus looses its function, and unconscious selection leads to retention
of the seeds on the mother plants. Most obvious is the shift from shattering
spikes or panicles (in wild cereals) to the non-shattering condition (in their cultivated
counterparts), and the parallel development of non-dehiscent pods in domestic
pulses. In most grain crops tested (e.g., wheats, barley, lentil, pea), the shift to nonshattering
or non-dehiscence is being controlled by a single principal mutation, or by
two such mutations.
Even and rapid seed germination: A second major outcome of introducing the wild
grain plants into the regime of sowing and reaping is the loss of the wild-type seed
germination regulation (HARLAN et al.1973, HEISER 1988, ZOHARY and HOPF 2000,
pp.18, 93). Under cultivation, there is a premium on even, rapid germination; and the
wild adaptation of seed dormancy breaks down.
Other traits of grain crops that could have been moulded by unconscious selection:
Several other traits seem to have been automatically selected for, once grain plants
have been introduced into agriculture (HARLAN et al. 1973, HEISER 1988).
These include:
• A shift towards more erect habit, synchronous tiller production, and uniform seed
ripening.
• Increase of seed numbers: by addition of fertile ovules to spikelets, pods, etc; by
increase of the size of the inflorescences (spikes, panicles, flowering branches);
or by increase of the numbers of such inflorescences per plant.
• Increase in seed size.
• Breakdown of the camouflage coloration of seed coats (particularly in pulses).
Concluding remarks
A main reason for presenting this paper has been the realisation that there is a need
to re-evaluate unconscious selection under domestication; and to better understand
the role of this kind of selection in shaping cultivated plants. To day, the wild ancestry
of many of our crops (particularly those domesticated in Southwest. Asia and the
Mediterranean basin) is already relatively well identified. The ecological specificities
of several of these wild progenitors are also extensively studied. Moreover, the archaeological
information on the rise of farming in these territories is quite extensive.
In conclusion, compared to the situation some 15-20 years ago, more reliable
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