Classic Genetics and Breeding - Genetics, Genomics and Breeding of Crop Plants - page 57

maintained by breeders either in isolated plots (where pollination is carried
out by bees) or by a series of sib-crosses under paper tubes or cloth bags,
with mixture of the seed of all plants harvested in order to maintain
variability.
The last widely grown open-pollinated varieties were highly self-sterile,
since self-sterility was in fact a favorable character to obtain a maximum of
hybrid plants in the population and therefore the highest yields. However,
the fact that these open-pollinated varieties were made up of a population
of different hybrids meant that they were not uniform for important
characters, such as height or earliness. Breeders followed the example of
maize and, from 1950 onwards, became interested in hybrid varieties. The
development of modern breeding programs to create hybrid varieties was a
radical change since it was necessary to have homozygous, inbred parental
lines that could be maintained and thus were self-fertile. It was not really
possible to maintain breeding for both open-pollinated varieties and hybrids
although there would have been a continued market for the former in some
developing countries where farmers did not wish to buy seed each year.
2.2 Hybrids
The first studies of hybrid vigor in sunflowers were made during the late
1940s by Canadians, who found an increase of 60% in yield compared with
open-pollinated varieties (Unrau and White 1944). They produced some
hybrid varieties, such as “Advance” between 1946 and 1952, using self-
sterility to facilitate crosses between parental lines. However, the proportion
of hybrid plants was often only 50% as it was impossible to use highly self-
sterile parents, since they could not be multiplied.
Many recessive genes causing male sterility are known, but, to be useable
in hybrid production, it is necessary to be able to distinguish the plants that
will be male sterile from those that will be male fertile, before flowering. The
gene linked with only 1% recombination to a gene controlling anthocyanin
production, reported by Leclercq (1966), fulfilled this condition since the
plants that carried the male fertile allele produced anthocyanins at the
seedling stage onwards and thus could be eliminated, leaving only non-
anthocyanin male sterile plants at flowering to be pollinated by the male
parent inbred ( Fig. 2-1 ) . This male sterility becomes apparent during pollen
maturation, a few non-viable pollen grains being present in the anthers at
flowering. Normal sunflower lines without the male sterile gene were used
as male parents. Hybrid varieties using this system were developed by INRA
from 1969 (“INRA6501”) to 1975 (“Airelle”) and grown up to about 1980.
However, two important problems appeared as discussed below.
With a recessive gene, the maximum proportion of male sterile plants in
a progeny is 50%, obtained from crossing the homozygous recessive ms/ms