Hayes and Garber - Cucurbit Breeding

92 BREEDING CROP PLANTS
development. Nilsson-Ehle (191 la) first used the hypothesis
that the yellow gene inhibited the development of awns. This
hypothesis was substantiated by careful experiments. A number
of crosses betwen Avena fatua, hairy awns on both grains,
with early oats belonging to the Avena saliva group have been
studied. Using Sixty Day with yellow grains as the awnless
parent, Love and Craig (1918c) observed the FI to have
the lower grain often awned but the upper grain awnless.
They
concluded that the yellow factor inhibited the complete development
of awns. In a similar cross, Surface (1916) obtained like
results in FI and concluded that one main factor difference was
necessary to explain the results. Modifying factors were involved
which affected the degree of development of awns. No significant
evidence was found that the yellow gene inhibited the
development of awns.
Fraser (1919) has studied a cross between an awnless Sixty
Day and Burt, the latter being a variety of the A vena sterilis
group. The Sixty Day parent produced bright yellow grains
with no awns. The Burt parent usually produced awns on the
lower grains and frequently on the upper but they show weak development.
Fraser classified awns as strong, intermediate, and
weak. The strong awn is twisted at the base and has a sharp
bend about three eighths of the way from the base to the tip. It
The intermediate awn lacks the bend of the
is also stiff and long.
strong awn and is less stiff. It is generally twisted at the base
and is often curved. The weak awns vary greatly from almost
imperceptible structures to weakly developed ones. The FI
plants of Burt X Sixty Day were practically awnless. In Fz
there was a ratio of fully awned (awned like Burt or with awns
more completely developed) to awnless and partly awned of 1 :
3. The fully awned bred true in later generations. Results
substantiated the hypothesis that Sixty Day carried a factor for
awning which was inhibited from development by the yellow
factor.
Color of Grain and Straw. Color of the lemma when ripe
is a character which is easily affected by environment. Weather
conditions at ripening are important and greatly modify the
expression of inheritance of these color characters. With bright
sunshine a deeper color is developed than in wet, cloudy weather.
Black or yellow grained varieties under unfavorable environmental
conditions are much less intensely colored, The stage of matu-