Hayes and Garber - Cucurbit Breeding

CLASSIFICATION AND INHERITANCE IN WHEAT 81
chaff,
Spike Density. Compactness of spike, color of seed and
texture of seed, and presence or absence of awns are frequently
used in wheat variety classification.
Nilsson-Ehle (19116), in crosses between compact and squarehead
(mid-dense) wheats, obtained compact forms in FI and
segregation into compact, mid-dense and lax in F%. He explained
the results by supposing the main factor differences to be as
follows;
Swedish Binkel (compact) CCLiLiL 2Z/ 2
Squarehead
cclililzh
The C factor was considered to inhibit the expression of the
lengthening factors Z/i and L 2 ,
and also to produce spikes with
short internodes. While these factors gave a satisfactory
explanation of his crosses Mayer Gmelin (1917) showed that they
did not explain the production of compact spiked forms which he
obtained from crosses of spelt (lax) and Essex Velvet Chaff,
which is mid-dense. In F z generations grown from individual
plants of a cross between white spring emmer and Marquis,
studied at the Minnesota Experiment Station, a very common
sort of segregation was from lax, keeled, speltlike wheats to
compact, keelless, naked wheats. This might indicate that
spelt wheats contain a compact factor which is prevented from
expression by some other genetic factor.
Crosses between T. compactum and T. vulgare by Spillman
(1909) and Gaines (1917) have shown one main factor difference
for compactness. Parker (1914) made careful measurements of
internode length in crosses of wheats belonging to T. compactum
with those of T. vulgare. He was able to demonstrate segregation
but found the condition very complex. Results of this nature
have been satisfactorily explained by the multiple factor hypothesis.
The number of factors involved cannot accurately
be determined. Nilsson-Ehle, likewise, states that besides the
main factor differences there are other minor factors which
influence spike density and account for a wide range of homozygous
forms.
Seed Characters.
Color of seed, which results from a brownish,
red pigment in one of the bran layers (remains of nucellus)
has been quite consistently used in variety classification. This
is a plant character and not, therefore, immediately affected by
pollination. Red is dominant over white and in the second
G