Agriculture Reference
In-Depth Information
resentative leaf per plant on a representative sample of individual plants
instead of taking one measurement on the population in its entirety (the
DUS method). Spinach plants are diffi cult to characterize because the har-
vested organ is the leaf, during the vegetative growth period of the plant.
Furthermore, as each plant has multiple leaves, one observation does not
necessarily represent the plant in its entirety, as could be considered for the
maize ear for example. However, we tried to balance this potential source
of error by sampling a large number of individuals per plot and rigorously
adhering to a set protocol in leaf selection and measurement.
Other than the phenological traits, all the traits we observed are also
included in DUS tests. These are traits that display genetic differences be-
tween varieties and that are not too much infl uenced by the environment.
This is also likely the case for phenologicaly traits, which are of adaptive
signifi cance, as is known in other species [14]. Most of these traits are also
likely quantitatively inherited. Therefore, we expected they would react to
natural and/or human selection. The changes observed can thus be linked
with natural adaptation (pressure of the environment), possibly farmers'
selection, and also a certain degree of chance (genetic drift or accidental
pollination during the multiplication phase, even though multiplication
was controlled very carefully). The changes could also be due to different
multiplication methods. Varieties coming from gene banks are maintained
with a strict scheme, with the aim of conserving a specifi c phenotype of
the variety. The method applied by farmers differed from this scheme and
this could explain part of the observed changes.
At the least, we can say that the varieties tested in this study have
changed in only two years of cultivation. We interviewed farmers on their
selection criteria throughout the project to see if human selection could
have had a directional infl uence on the phenotypic changes observed.
12.3.2 EFFECT OF FARMER SELECTION ON CHANGES IN
THE VARIETIES
Selection criteria applied by the three farmers of this study are described
in Table 3. AVO selected plants only on precocity and 'Monarch Long
