Hayes and Garber - Cucurbit Breeding

GRASSES, CLOVER, AND ALFALFA 215
tions induced the formation of a large percentage of infertile
ovules. All the cells remained sporophytic, no reduction taking
place with the formation of an embryo sac. As much as 100
per cent, ovule infertility was found in the first clover crop.
The rate of pollen tube growth was shown to be much slower in
self- than in cross-pollinated plants. It is probable that pollentube
growth is too slow to effect fertilization when the plant is
selfed. The pollen of red clover is easily burst by an excess
supply of moisture. Martin (1913) demonstrated that good
artificial germination of pollen could be obtained on membranes
which were just moist enough properly to regulate the supply of
water to the pollen. He suggests that the stigma of red clover
performs the same function as the membranes.
The above facts necessitate a method of breeding which
is essentially a restricted form of mass selection.
Before starting
selection it is desirable to make comparisons of the varieties produced
by other breeders and of commercial seed from different
sources to obtain the best form for further breeding operations.
A seed plot may then be used, in which each plant is spaced
so that its characters may be determined. Undesirable plants
should be removed before pollination. By repeating this process,
forms with the desired characteristics and with practical uniformity
may be isolated.
Selection for Disease-Resistant Clover.
Clover anthracnose
(Colletotrichum trifolii], causes serious injury to red clover in
certain regions. Bain and Essary (1906) issued a preliminary
report on isolating an anthracnose resistant red clover. Healthy
plants in a badly infested field were located late in the season
after most plants had been killed by the disease.
The seeds of
the chosen plants were planted separately in alternate rows with
ordinary commercial seed. Measures were taken to insure the
infection of every seedling with anthracnose. By June 1 the
commercial plants began to show symptoms of the disease and
by the middle of September not more than 5 per cent, of them
were living, while 95 per cent, of the selections were healthy
and making a fair average growth. Some of the latter showed
small lesions, but growth was not seriously injured.
ALFALFA
Alfalfa is one of the oldest, if not the oldest, plant cultivated
for its forage only (Piper, 1916). Most of the cultivated forms