Hayes and Garber - Cucurbit Breeding

116 BREEDING CROP PLANTS
of selections of like nature together, the use of single rows
and more replications, may be desirable under certain conditions.
6. Computation of a probable error for the method of test.
The use of this probable error as a means of determining significant
differences.
7. Increase of the better selections and either a trial by careful
farmers or a further test in field variety plots followed by distribution
of the better strains. If placed in field variety plots,
borders should be removed and each variety tested in replicated
plots. Probable errors should be obtained and used as in
the row trials.
From five to eight years' time is needed before the new
selection is introduced to the farmer.
Crossing. The improvement of commercial varieties of self
fertilized small grains by the head or plant method of selection
is a very easy process, although several years are required to do
the work. The production of new forms by crossing is not so
simple. A' standard plan of attack has been developed which
is the application of the Mendelian method.
The first step is the initial cross. Promiscuous crossing is not
advised, but each cross should be the result of a determination
of parents which most nearly approach the ideals in mind. By
recombination of characters there is the possibility of obtaining
a sort which is more desirable.
The FI generation is grown so that each plant has space for
individual development. A knowledge of the inheritance of
characters allows those plants which are not crosses to be eliminated
in FI. The F 2 generation plots should be as large as can be
studied and each plant grown with enough free space that it may
be examined. Numerous selections of plants which have desirable
field and seed characters should be made. Each of these
F 2 plants selected should be grown in an individual progeny plot in
F 3 and individual plant notes taken. Selection of desirable
plants should be continued in later generations. When plots
show apparently uniform progeny of a desirable sort, the strain
should be included in the rod-row tests and compared with
standard varieties.
Knowledge of the results of continued self-fertilization in
generations following a cross, shows the reliability of another
method which was first used at Svalof, Sweden (Babcock and