Hayes and Garber - Cucurbit Breeding

178 BREEDING CROP PLANT*
which are resistant to wilt. A number of resistant high-yielding
varieties have been introduced in the cotton growing regions of
the United States. The character of wilt resistance was transmitted
in crosses but nearly every cross gave a
different result.
In general, resistance proved dominant but there was often considerable
variability, possibly due to the gametic composition
of the parents or to the nature of the reaction between the disease
organism and the host plant or to the lack of uniform evironmental
conditions. Wilt resistance does occur and varieties may be
obtained which are resistant and are also of good quality with
respect to yield and staple.
SORGHUM
Origin. The numerous diversified forms of sorghum indicate
that it has been cultivated a long time. Evidence has been found
that it was grown in Egypt as early as 2200 B.C. Hackel places
all the cultivated sorghums and the various forms of Johnson
grass in one botanical species. It has been pointed out by Piper
(1916) that two species exist the perennials, Johnson grass and
its varieties (Andropogon halepensis), and the annual sorghums
(Andropogon sorghum). The former possesses rootstocks, and
it is difficult to cross it with either the cultivated or wild forms of
sorghum.
The wild annual sorghums, which are found almost exclusively
in Africa, cross readily with the cultivated forms. Africa is
thought to be the native home of our cultivated sorghums.
Classification and Inheritance. On the basis of the three
economic characters production of grain, sugar, and broomstraw
three distinct types of sorghums have been developed.
All of these produce forage and some of them, as Sudan
grass, are grown primarily for this purpose. Piper, after Ball, has
suggested a group classification for all the forms of A. sorghum,
cultivated in America, to which the student is referred (Piper,
1916). Only a brief statement will be given here. Smallstemmed
sorghums, such as Sudan-grass and Tunis-grass,
comprise one group. The other group, the large-stemmed sorghums,
are divided on the basis of the character of the pith
whether it is juicy or dry. The juicy sorghums may be either
sweet or slightly sweet to sub-acid. The dry sorghums are further
classified into varieties on the basis of panicle characteristics.
Hilson (1916) found that a pithy stalk was dominant