Hayes and Garber - Cucurbit Breeding

CHAPTER XV
GRASSES, CLOVER, AND ALFALFA
The importance of hay crops in the world's agriculture makes
desirable their consideration from the standpoint of improvement
by breeding. Grasses, clover, and alfalfa differ strikingly
in (see Chapter III) amount of seed set when artificially selfpollinated.
Red clover (Trifolium pratense) is practically selfsterile;
white clover (Trifolium repens) sets few seeds when
protected from insect pollination; timothy (Phleum pratense)
under a bag produces few seeds; and brome grass (Bromus
arvensis) under the same conditions sets seed abundantly.
Although common alfalfa (Medicago saliva) and yellow alfalfa
(M. falcata) cross freely, seed of either may be produced by
selfing. Enough examples have been cited to show that there
are not only differences in the modes of pollination in the
three mentioned classes of hay crops but also differences within
each class. Carefully controlled experiments with grasses to
determine the percentage of naturally crossed and naturally selffertilized
seed are very
limited. To what extent decrease in
is also an un-
vigor will result from artificial self-pollination
answered question. When self -sterility is not a limiting factor,
the methods of breeding all these crops are essentially alike.
The ease with which some of them may be clonally reproduced
has led to slight modifications in breeding technic. In the
following brief discussion, the aim has been to choose a few
examples rather than to enter into an exhaustive treatment of
the entire field.
GRASSES
Timothy ranks far ahead of the other grasses in importance.
Some of the other hay grasses which may be mentioned are
orchard grass (Dactylis glomerata), tall oat-grass (Arrhenatherum
elatius) and brome
, grass (Bromus inermis)
. These three grasses
are adapted to certain conditions better than is timothy. Some
important pasture grasses are Kentucky bluegrass (Poa praten-
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