Hayes and Garber - Cucurbit Breeding

FLAX AND TOBACCO 163
The Broadleaf variety is commonly grown in one section of the
Connecticut Valley and is especially valuable for cigar wrappers.
Sumatra which is an imported variety produces many leaves
per plant but they are small. As may be seen from an examination
of the table, the FI had an intermediate number of leaves.
Segregation occurred in F 2 and selected F 2 plants gave F 3 families
which differed in the average number of leaves. 5-1-14, showed
the lowest coefficient of variability of any F 3 family. Progeny
of this same F 2 plant were also grown at another locality and
they proved uniform in number of leaves, the calculated coefficient
of variability being 6.44 + 0.27. #-1-10 gave a low coefficient
of variability and a mean leaf number which was about the
same as in the FI generation, i.e., intermediate between the
parents.
A cross
was studied between Connecticut Havana, which is
grown as a wrapper and binder tobacco both in the Connecticut
Valley and in Wisconsin, and Cuban, a variety commonly grown
under shade. The parents and FI gave about the same number
of leaves but in F 2 there was a great increase of variability, forms
being obtained with a higher and lower leaf number than in either
parent. The inheritance of size and shape of leaf was likewise
investigated. The Cuban variety gives a short broad leaf and
the Havana a longer leaf which is proportionally narrower than
the Cuban. Lines were obtained in F 3 which bred true, respectively,
to the parental leaf shapes.
East (1916a) has listed eight requirements, most of them independent
mathematically, which should be met if size inheritance
is typically Mendelian, when all populations succeeding the
original cross are obtained by growing progeny of single selffertilized
plants. These are:
"1. Crosses between individuals belonging to races which from long
continued self-fertilization or other close inbreeding approach a homozygous
condition, should give FI populations comparable to the parental
races in uniformity.
"2. In all cases where the parental individuals may reasonably be
presumed to approach complete homozygosity, F 2 frequency distributions
arising from extreme variants of the FI population should be practically
identical, since in this case all FI variation should be due to
external conditions.
"3. The variability of the F 2 population from such crosses should be
much greater than that of the FI population.