Hayes and Garber - Cucurbit Breeding

CHAPTER III
THE MODE OF REPRODUCTION IN RELATION TO
BREEDING
General recognition of the stability of inherited factors has
served to emphasize the importance of a knowledge of the mode
of reproduction of crop plants. If the crop in question
is normally
self -fertilized, and has been bred carefully, accidental
crosses may cause serious mixtures in the variety and thus
prohibit its sale as pedigreed seed. With naturally crossfertilized
plants, self-fertilization often has a detrimental effect.
A knowledge of the mode of pollination of a crop is therefore
an absolute necessity in outlining correct methods of breeding.
As with other characters, environmental conditions play an
important role. With crops which are adapted for insect
pollination and yet which are self-fertile,
the number and sort
of insects found in the locality may greatly modify the amount of
crossing which takes place. Variations in moisture conditions
may determine the amount of cross-pollination. The age of the
plant also is of importance. Aside from these there are often
varietal differences in closely related forms.
Plants may be placed in four groups according to their
mode
of reproduction. These groups, however, overlap because of
prevailing conditions and inherent differences which the plants
exhibit.
Group 1. Naturally self -pollinated : Wheat, oats, barley,
peas, beans, flax, tobacco, tomatoes, cotton, sorghums. 1
Group 2. Often cross-pollinated: Maize, rye, sugar beets,
root crops, grasses, alfalfa, cucurbits.
Group 3. Cross-pollination obligatory: (a) Self -sterile, red
clover, sunflower, many fruits; (6) Dioecious plants, hops,
hemp, asparagus, and date palm.
1 Some crops, such as sorghum and cotton, cross in the field frequently.
As there is no sharp line of demarkation between cross- and self -pollinated
plants and as sorghum and cotton should apparently be handled by the
breeder in much the same .manner as crops like barley, which is seldom
naturally cross-pollinated, it seemed wiser to place sorghum and cotton in
the self-fertilized group.
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