Hayes and Garber - Cucurbit Breeding

252 BREEDING CROP PLANTS
kohl-rabi. The parental forms did not appear in the F 2 generation.
Drumhead cabbage crossed with Thousand-headed kale
produced 204 plants in F*. Of these, 176 resembled a dwarf
type of Thousand-headed kale with leaves broader than usual
and fewer branches; 26 resembled cabbage; and two plants
were much like brussels sprouts.
The difficulty of a study of inheritance in the Brassica genus
arises from the heterozygous condition of many forms and the
self-sterile condition. Before the results are accepted as examples
of non Mendelian behavior, a criticial study in which all
facts are considered should be made. In cabbage there is apparently
a complicated inheritance. The above results are satisfactorily
explained on a multiple-factor hypothesis.
In crossing
heterozygous forms, the FI generation may be as variable as the
F 2 . In the inheritance of any particular character, the number of
factor differences may be so large as to make the appearance of
parental forms improbable in a small F 2 generation.
Breeding. The breeding of cabbage resistant to yellows (Fusarium
conglutinansWollenw.) at the Wisconsin Experiment Station
(Jones and Oilman, 1915) is of great economic importance.
Less than a decade ago, truck farmers in certain sections of Wisconsin
were so discouraged from the ravages of yellows that they
were about to abandon cabbage growing. The method of producing
resistant cabbage strains may be briefly summarized.
It had been noticed that there were usually a few plants which
escaped the disease in a field where nearly all plants were badly
infected with the organism. These apparently resistant plants
were selected on the basis of type. After storing over winter,
all that were of the same general type were planted together
and were far enough removed from any other similar planting
to insure against contamination by foreign pollen. Selfed
seed was not obtained but most plants not bagged set seed
abundantly. Some plants were eliminated because of low seed
production. Progeny of the retained plants were grown separately
and their resistance to yellows was tested. In this way
several strains of cabbage highly resistant to yellows have been
produced. Further studies have been reported and numerous
resistant varieties have been produced (Jones et al, 1920). The
writers emphasize the fact that resistance is not absolute and
that environmental factors influence very markedly the development
of the disease. They state, however, that: