July 15,1925 
Bean Varietal Tests for Disease Resistance 
109 
inoculation. It soon became evident, however, that wilting alone 
was a poor index for comparison, since practically all plants inocu¬ 
lated snowed this symptom. On account of more or less abnormal 
growth of both inoculated and control plants under ordinary green¬ 
house illumination in the winter, it was unfortunately not practicable 
to conduct the experiments for a longer period. A number of tests 
on potted plants carried for two months brought out much greater 
differences and showed that a longer experimental period is essential. 
The field seedling inoculations, therefore, gave a much better test of 
the ultimate effect of this disease on the plant than either the green¬ 
house seedling tests or the field inoculations on older plants. 
WEATHER CONDITIONS AND PREVALENCE OF ANTHRACNOSE 
AND BLIGHT DURING THE PERIOD OF TEST 
ANTHRACNOSE 
During the entire period 1920 to 1923, inclusive, weather con¬ 
ditions were in general unfavorable for natural spread of anthracnose 
at both the Saginaw and East Lansing plots. At McMillan, Mich., 
on the other hand, epidemics developed during both years (1921 and 
1922) that plots of American varieties of beans were maintained 
there. The usual midseason hot, dry spell at Lansing effectively 
checked the spread of the disease until the cool, moist weather of 
late summer. Conditions in 1920 and 1923 were not so unfavorable 
as to prevent the obtaining of abundant infection by repeated 
artificial inoculations, so that not only were epidemics produced 
in the two 1923 Michigan plots, but Doctor Leach reported satis¬ 
factory results in the duplicate established at St. Paul, Minn. A 
fairly decisive test was, therefore, obtained on all varieties planted 
in 1923 
BACTERIAL BLIGHT 
Bacterial blight was generally prevalent and severe in all test 
plots during 1920, 1921, and 1923, and also on the late varieties 
following the extreme dry period of 1922. The disease was so 
destructive in parts of the Michigan bean section in 1921 that a 
number of fields of Red Kidneys were not harvested. 
RECORDS OF DISEASE PREVALENCE 
The data on the reaction of each variety to the various diseases, 
obtained from the different field plots during the entire period of 
test and from the greenhouse inoculations, have been critically re¬ 
viewed and classified according to six standard grades of infection 
extending from very severe at the one extreme to none at the other. 
Brief definitions of these classes, which necessarily depend upon a 
different set of symptoms for each disease, are given in Table I. 
Unfortunately suficient knowledge of the diseases and refinement 
of techinque are lacking to enable one to give a more definite expres¬ 
sion of resistance or susceptibility than is shown by the headings of 
Table I. This is especially true in the case of bacterial wilt, where 
the progress of the disease under varying field conditions is poorly 
understood. Likewise difficulties are encountered in attempting to 
define clearly what appear to be intermediate degrees of suscepti¬ 
bility to bacterial blight. For mosaic, prevalence has been largely 
relied upon, although, as mentioned earlier, the data on this disease 
were obtained incidentally as they were available in the course of 
the other studies. 
59837—25f-2 
