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Genetic
background To understand the background of some cultivation methods
it is inevitable to look at the special genetics of the genus corn.
In
all corn forms, male and female flowers grow separate from each
other on the same plant. The male flowers (delivering pollens) are
situated in the panicle, whereas the female flowers develop in the
leaf axillas on an ear, which has the shape of a cob. Thus, corn
is a cross-pollinated plant with the wind transporting the pollens.
The
ears contain large quantities of the female flowers, arranged in
regular rows, which later form the kernels. From each of them arises
a threadlike pistil with a length of up to 50 cm. These pistils
are necessary for the pollination. The 300 - 900 pistils of all
flowers on one ear form a "tassel". At the time of pollination they
stand out from the leaves which wrap the ear.
About
2 - 4 days before the pistils develop, the same plant produces pollens
in large numbers (aprox. 4,5 millions/ panicle). This is a process
which supports the cross-pollination, and thus, the pollination
is generally caused by the pollens of another plant (aprox. 95%).
Each pistil must be pollinated to achieve a regular arrangement
of kernels on the ear.
Each
pollen includes two cell nuclei with a complete set of the genetic
information of the pollinating plant (haploid). After the pollination
with the ovum, which contains a single set of maternal chromosomes,
one of these nuclei forms the embryo, which then includes paternal
and maternal genotypes.
The
second nucleus of the pollen combines with the duplicate maternal
chromosome set of the nutritive tissue (endosperm) to form the so-called
triploid nucleus (threefold chromosome set), which contains a duplicate
set of the maternal chromosomes and a single set of the paternal
chromosomes.
The
main part of the kernel consists of this triploid nutritive tissue,
the characteristics of which are determined by the combination of
the genetic information on the chromosomes (= genes).
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