Hayes and Garber - Cucurbit Breeding

MAIZE BREEDING 205
of its characters.
Fi crosses are of value from the standpoint of
earliness. Thus a cross, studied at Minnesota in 1919, between
Squaw flint and Minnesota No. 13, approached the dent parent
in height of plant and the flint parent in earliness and exceeded
both in yield. Such a cross would be of much value as a silage
or husking variety under northern conditions.
The production of crossed seed is not very difficult. The varieties
to be crossed may be planted in alternate rows and the
tassels removed from one variety before any of the pollen has
matured. Seed produced by the detasseled variety is known
as first generation crossed seed. If the varieties to be crossed
differ in maturity they should be planted at different times so
that both bloom at about the same date.
Isolation of Homozygous Strains. Shull (1908, 1909) first
suggested the utilization of crosses between self-fertilized strains
as a means of increasing yield in corn. Such crosses often give
very high yields. The chief objections to this method are that
self-fertilized strains are usually of very low yielding capabilities
and that the seeds from selfed lines are usually much smaller than
from normally pollinated corn. Even though crosses between
self-fertilized lines yielded very vigorously, the method has not
seemed commercially desirable. Low yields of seed per acre
would increase the cost of seed. Under unfavorable conditions
the food supply of the seed might not give the young FI plant a
vigorous start. Jones (1918) has made a suggestion which
removes some of these objections. After isolating selfed strains,
tests are made to determine which four biotypes are most desirable
as parents. Suppose these are numbered 1, 2, 3, and 4
respectively. Numbers 1 and 2 are crossed, also 3 and 4, by
detasseling all of one biotype in each group. Seed from the
plant^ of each detasseled biotype is then planted in alternate
rows in an isolated plot and all of one combination, as 3 X 4,
detasseled. Seed from these detasseled rows is used for commercial
planting.
This method seems worthy of more extensive trial. Such a
cross was compared at the Connecticut station with the best
dent variety obtained from a varietal survey followed by a variety
test. The highest yielding dent variety gave a yield of 92 bu.
while the cross under similar conditions yielded 112 bu.
Every investigator who has produced self-fertilized strains of
corn has been impressed by the large number of undesirable