Hayes and Garber - Cucurbit Breeding

CHAPTER X
SOME RESULTS OF CROSSING AS A MEANS OF
IMPROVING SELF-FERTILIZED CROPS
In the preceding chapters it was shown that the selection
and increase of a homozygous individual plant isolated a pure
line. No one of these pure lines contains, as a rule, all the
characters desired. What usually happens is that one pure
line excels in one character, while another is superior with
regard to some other character. The only way in which the
desirable characters belonging to different strains can be combined
is by crossing and then selecting the desired segregate.
To attain success in this field, it is important to use as parents
those forms which most nearly approach the combination of
characters desired. The old idea of indiscriminate crossing in
order to procure superior economic characters, such as yield,
has been largely abandoned, which is reasonable from our knowledge
of what selection accomplishes and of Mendel's law of inheritance
in crosses. Love (1914) compared the yield of oat
selections with hybrids which were the result of more or less
indiscriminate crosses made by J. B. Norton. The average
yield of the hybrids was but little higher than the average yield
of the selections. It is probable that the comparison would have
shown a greater difference if the parents had been chosen on the
basis of their performance records.
Two forms may be crossed
because each possesses to the greatest degree the character sought,
with the hope of obtaining transgressive segregation; or a cross
may be made to combine different characters.
The Improvement of Black Oats at Svalof. Nilsson-Ehle
(1917) has reported experiments carried on from 1901 to 1917 for
the purpose of improving the black oats grown in Sweden. The
native oats formerly grown had weak straw and lodged badly.
Black Tartarian oats was introduced to overcome this difficulty.
Little by little this form mixed with the native oats and probably
naturally crossed to some extent. The resultant complex (Svart
Tartarish Plymhafre) was especially suitable for selection and the
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