June 15, 1921 
Varietal Susceptibility of Beans to Rust 
403 
sisted of small telia borne in the centers of flecks. No infection was 
obtained on the horse bean, the asparagus bean, nor on any variety of 
cowpea. 
A second form distinct pathologically from the foregoing but similar 
morphologically was isolated in 1919 from leaves of cowpeas, variety Black 
Eye, which were sent us from California by Mr. D. C. Milbrath. It has 
been cultured in the greenhouse on plants of this variety and has been 
used for both greenhouse and field inoculations on a number of varieties 
of kidney beans and 18 varieties of cowpeas. Infection has been ob¬ 
tained on only the Black Eye variety of cowpea and on two similar strains, 
Extra Early Black Eye and Ramshom Black Eye. No tests have been 
made on lima, horse, tepary, or asparagus beans. 
These two strains may be designated the kidney-bean strain and the 
cowpea strain. They are distinct biologically, but their host ranges 
are as yet imperfectly known. It is possible that more than one 
biologic form occurs on kidney beans, but such evidence as is at hand 
would indicate that the strain which occurs commonly on kidney beans 
in the United States has the same host preferences as the one we have 
studied. The behavior of varieties in Maine, as observed by Morse (9), 
agrees in all essentials with our data, and the general mention of rust 
on Kentucky Wonder in other States points to this conclusion. It 
seems probable that a distinct biologic form occurs in South America. 
Gassner (5) records rust as severe on Mont d’Or and Flageolet, two- 
wax-pod varieties, while our strain produced flecks only on these. It 
is possible, however, that the varieties grown under these names by us 
were distinct from those used in South America. Gassner obtained 
his seed from Europe. 
SUMMARY 
A technic of inoculation and method of record is described which 
makes possible the expression of the relative rust susceptibility of 
varieties of beans in terms of percentage of a standard. 
Variations from the behavior of the susceptible standard which occur 
in different varieties following inoculation with urediniospores in the 
greenhouse are of the following types: (a) reduction in number of 
infections, (6) reduction in the size of the uredinium, ( c) abortion of 
infection or flecking, (d) immediate production of telia instead of 
uredinia, (e) lengthening of the incubation period. These variations 
are considered as responses to an unfavorable medium and as expres¬ 
sions of resistance. 
Of the varieties studied, those with indeterminate growth (pole beans) 
were more susceptible as a class than those with determinate growth 
(bush beans). Green-pod varieties were more susceptible as a class 
than wax-pod varieties. With respect to color of seed all varieties 
with solid red or red mottled seed were rust resistant, while varieties 
with white seed were more susceptible as a class than those of any 
42270°—21-3 
