Hayes and Garber - Cucurbit Breeding

82 BREEDING CROP PLANTS
generation a ratio of 3 red-seeded plants to 1 white-seeded plant
is often obtained. Nilsson-Ehle (19116) was the first writer
who reported crosses which in F 2 gave 15 to 1 or 63 to 1 ratios of
red- and white-seeded plants. The Howards (1912), in India,
have obtained 63:1 ratios in crosses of American Club with pure
lines of Indian wheats, and Gaines (1917) in Washington, has
obtained similar results from a cross between Bluestem (red seed)
and Brown's Glory (white club wheat). Nilsson-Ehle obtained
a ratio of 15 red-seeded plants to 1 white-seeded plant from a
cross of two red-seeded varieties. The inheritance of this seed
color has been explained by one or more Mendelian factors,
each when present giving red and when absent white. The
factors are separately inherited, each when homozygous producing
somewhat darker color than when heterozygous. They are
also cumulative, two factors giving a darker color on the average
than one of these factors alone.
It is impossible, by inspection,
to determine how many factors are responsible for a particular
varietal seed color.
Texture of seed has also been used in varietal classification and
is a character which determines to some extent the market class
in which the variety will be placed. Biffen (1916) found immediate
effect of pollination in a cross of Rivet, a hard-seeded
turgidum with pollen from a soft Polish variety. The F\ generation
plants produced hard seed and the F% segregated into
hard- and soft-seeded plants in a ratio of 3:1. The Howards
(1915) obtained an intermediate condition mFi plants and a 1 : 2: 1
ratio in F z in crosses between hard- and soft-seeded strains.
Freeman (1918) crossed hard-seeded durums with T. vulgare,
variety Sonora, a soft-seeded wheat. The FI plants produced
hard, intermediate, and soft seeds. The hard seeds of the FI
tended to give more hard-seeded plants in F 2 ,
and the soft-seeded
tended to give more soft-seeded plants. Freeman carried the
study through F 4 . He explained his results on the basis of two
factors for starchiness, each inherited independently. He
supposed each to produce half as much soft starch when heterozygous
as when homozygous. As the endosperm is the result of
the fusion of two polar nuclei with one of the male generative
FIG. 19. Representative spikes of F 3 families of the cross between Durum
and Marquis. Upper 4 groups, Fa families which were classified as durums.
Note that they represent all types of spike density. Lower left, spikes of an
awnless F 3 Emmer family. Lower right, four spikes of an F 3 plant which resembled
common wheat in spike shape and which proved rust resistant.