Hayes and Garber - Cucurbit Breeding

76 BREEDING CROP PLANTS
Classifications of some crops have recently been made and in the
next few years these will be improved further. The general
adoption of some standard variety classification is a necessity
if
work of different investigators in crops is to be correlated.
The central aim in crop improvement work is to find or produce
improved forms which when grown by farmers will excel in
quality, productivity, or ease of handling. It is a decided
advantage if the improved form can be distinguished from the
varieties commonly grown in the locality by some botanical or
morphological character difference. Kanred (Jardine, 1917)
wheat is an example of a new variety with such a character.
This variety, which was developed at the Kansas station, belongs
to the Crimean group of winter wheats. It gives larger yields
on the average than Turkey or Kharkov selections and excels in
resistance to black stem rust, Puecinia graminis tritici, and
leaf rust, Pucdnia tritidni. Its beak, i.e., the extension of the
outer glume in the form of an awn point, is longer than in the
common forms of Crimean winter wheat grown in Kansas.
Marquis wheat, which is so widely grown as a spring wheat in the
Northwest and Canada, differs in seed shape from other Fife
wheats commonly grown in these sections. Forms belonging; to
the same variety may frequently exhibit differences in productivity
and this may be the sole distinguishing character difference.
Forms constantly differing from each other in one or more genetic
factor differences which may be expressed as yield, quality, or
disease resistance, or a minor botanical character and yet which
belong to the same variety group, may be called strains.
This
is the lowest order of classification which can be adopted for seeded
crops. With a self-fertilized crop the strain may also be a pureline
in the original sense as used by Johannsen. With crossfertilized
crops the strain may be relatively pure for some particular
character and may be heterozygous for other characters.
Inheritance studies of many of our farm crops have been made.
As crossing is the only means of inducing variation that can be
carried out with success by the plant breeder, it becomes necessary
to know how individual characters are inherited.
that yield is not a simple Mendelian character but is dependent
on many inherited factors and their manner of reaction to the
It is true
environment. At present, knowledge of inheritance may be
used only as a guide in working with these characters. As a rule,
the parental forms differ in botanical characters as well as in