Hayes and Garber - Cucurbit Breeding

114 BREEDING CROP PLANTS
Selection. The plant-selection method is used for the purpose
of isolating the best possible pedigreed strain of a commercial
If the variety is of considerable value a large number of
variety.
individuals (500 to 1,000) may be selected. Often a smaller
number is all that the breeder can afford to test. The number
chosen will depend on the productive capacity of the commercial
variety or new introduction which is used as the basis of selection.
Plant selections are grown in short rows the first year, the same
number of seeds being placed in each row.
Two general methods have been rather widely adopted for the
initial head-selection plot. In either method the same number
of seeds is placed in each row. The difference lies in the spacing
of the seeds. Some prefer to place the seeds approximately the
same distance apart in the row and at sufficient distance (2J^ to
3 inches) that the plants can be separately observed. Others
scatter the seeds in short rows, placing them so close together
that individual plants cannot be differentiated at maturity. The
latter method more nearly approximates the rod-row plan and
needs less room. In either case the rows are usually a foot apart.
The field, after being carefully harrowed, is raked by hand, if
necessary. It is then marked out by the use of a sled marker,
from 7 to 12 rows being marked at a time. The rows are opened
with a wheel hoe and covered either with it or a rake or a hand
drag with numerous iron teeth.
Those selections which by field inspection seem to be of inferior
to have weak straw or other undesirable characters, are
vigor,
eliminated before harvesting. A few others are discarded on
the basis of yield, although the experimental error in a yield
comparison of this kind is much too large to justify rejection.
The following year each selection may be grown,
if sufficient
seed is available, in three systematically distributed 18-foot
rows, 1 foot being removed from each end of every row before
harvesting.
According to Love and Craig (1918a), J. B. Norton, of the
United States Department of Agriculture, was the first to put
the rod-row method into general use. By varying the length
of the row and obtaining the yield in grams it is possible to convert
yields into bushels per acre by multiplying by a simple
conversion factor. If the length of oat rows harvested is 15 ft.
and the yield is obtained in grams, the yield per acre in bushels
may be obtained by multiplying by 0.2. For wheat and barley,