June 15, 1921 
Varietal Susceptibility of Beans to Rust 
40 x 
relative susceptibility of a variety in the field. The greenhouse test is 
seemingly a more severe one than the field test. Some varieties which 
have developed a few sori in the greenhouse have remained entirely rust- 
free in the field. It seems to hold true that a variety which develops 
less than 50 per cent fertile infection in the greenhouse does not suffer 
material injury from rust in the field, and conversely that a variety 
which exceeds 50 per cent infection in the greenhouse may be expected 
to suffer material injury in the field. No exceptions to the first rule 
have been noted and only two apparent exceptions, Golden Cluster and 
Kentucky Wonder Wax, to the latter. Both these varieties were 
conspicuously rusted in the field, but both yielded fair crops. It is 
impossible to state the degree of injury sustained by these varieties, since 
no rust-free plants were available for comparison. 
CURTAILMENT OF YIELD DUE TO BEAN RUST 
Attempts have been made to obtain data on the amount of reduction 
in yield caused by bean rust, but the nature of the pathogene makes the 
securing of reliable data almost impossible. Yield data from rusted 
and rust-free plants should preferably be obtained from alternating rows 
in the same plot, but it is impossible to maintain rust-free plants of 
susceptible varieties in the same plot with rusted plants. It was thought 
that the difficulty might be overcome by growing both resistant and 
susceptible varieties in separate isolated rusted and rust-free plots, the 
resistant varieties being used as a criterion of the relative crop-producing 
capacities of the different soils. 
A planting of this type was made in 1918 with Improved Goddard as 
the resistant variety and Navy Pea and Tennessee Green Pod as the 
susceptible varieties. The soil of the two plots was similar in physical 
properties and apparently so in fertility. All plants in the rusted plot 
were inoculated with urediniospores, and a general and severe infection 
resulted on the rows of susceptible varieties. The rust-free plot was not 
inoculated. It became infected naturally later in the season but not 
early enough to cause any material reduction in yield. Unfortunately 
the rust-resistant variety was so severely attacked by anthracnose that 
no reliable yield data could be obtained. The difference in growth and 
yield of the rust-susceptible varieties on the two plots was very marked, 
almost no beans being produced in the rusted plot. The yields of shelled 
beans for single rows 65 feet in length were as follows: Tennessee Green 
Pod, rust-free plot 267 gm., rusted plot 9 difference 95 per cent, 
Navy Pea, rust-free plot 494 gm., rusted plot 95 gm., difference 81 
per cent. 
A similar test was made in 1920 with three susceptible and three 
resistant varieties. The two plots were on the same piece of land but 
were separated by a strip of corn. Rust was very abundant on the sus¬ 
ceptible varieties in the inoculated plot, while the control remained free 
