Hayes and Garber - Cucurbit Breeding

BREEDING OF VEGETABLES 249
1. Those which are normally cross-pollinated but which set
seed freely on selfing and show no evidence of sterility.
2. Those which are wholly or partially self-sterile.
3. Those which are cross-fertilized owing to the dioecious
condition.
Much more study of the mode of pollination of vegetables is
necessary before it is possible accurately to classify vegetables
according to their mode of reproduction. The crops here
considered have been purposely chosen as illustrations of breeding
results within these three groups.
RADISH
Origin, Inheritance, and Breeding. The cultivated radish,
Raphanus sativus, was grown by the ancient Greeks and Romans.
There has been considerable discussion as to its origin. Some
writers have thought that the cultivated form with its fleshy
root arose directly from R. raphanistrum. This belief was apparently
substantiated by experiments in which the wild form
was grown under cultivation and after several years cultivated
radishes were obtained. Riolle (1914) tested this hypothesis by
a controlled experiment. The wild form was grown under cultivation
and self-fertilized. Three years of selection failed to
produce roots which resembled the fleshy roots of R. sativus.
On the other hand, when the wild and cultivated forms were both
grown on the same plot and seed was saved from the wild form,
it was found to be an easy matter, after three years' selection, to
obtain roots which resembled the fleshy roots of R. sativus.
These results were believed to be due to natural crossing of the
wild and cultivated forms. This hypothesis was tested by
making an artificial cross. Segregation for root condition occurred
in F 2 . This led Riolle to conclude that former experiments
in which cultivated radishes were obtained from the wild
through selection were best explained through natural crossing.
R. sativus roots contain sugar while wild roots contain no
sugar, FI crosses contain less sugar than the cultivated forms.
The presence of starch in the root of the wild radish, particularly
in the bark, is a character which separates it from the cultivated
varieties. This proved a dominant in crosses. Cultivated
radishes show various color intensities. Color is apparently
inherited in much the same manner as in other crops. Individual