Although it has been generally recognized that the difference in
potential amongst wheat
cultivars released in different eras is related to differences in their
reproductive sink strength, there
have been few investigations about changes in source–sink ratios
consequence of wheat breeding.
In the present study, two field experiments, in which plots were fertilized
irrigated and lodging
and diseases were prevented, were carried out with seven cultivars (including
representing different periods of plant breeding in Argentina from 1920
The cultivars were
defoliated during post-anthesis to analyse the response of grain weight
particular positions within
the spike (which have intrinsic differences in potential size).
Individual grain weight was virtually unaffected by defoliation in the
cultivars, but modern
cultivars exhibited a significant reduction in individual grain weight
several positions within the
spike, although this reduction was small (c. 15%) and many grains
unaffected. In addition, no
relationship was found between individual grain weight in the controls
reduction due to defoliation.
We concluded that if the source–sink ratio is further reduced,
yield of modern wheats will
be simultaneously limited by the source and the sink. Future breeding should
therefore attempt to
improve simultaneously both sink and source strengths.