Mar. 22, 1924 
Nematode Disease Caused by Tylenchus tritici 
927 
the healthy plants three lots of 100 culms each were similarly cut. In no 
case was any special selection made, the culms being taken as they came. 
Each lot of 100 culms from the infected plants was hand-threshed sep¬ 
arately. The galls were separated from the kernels in each case, and for 
each lot the weights of the straw, kernels, and galls were determined 
separately. Similarly, each lot of 100 culms from the healthy plants was 
hand-threshed separately. In each case the weights of the grain and of 
the straw from each lot were secured. The results are given inTable I. 
Table I .—Weight of straw and weight and volume of threshed grain from three lots of 
healthy and four lots of nematode-infected rye culms, 100 culms in each lot, Arlington 
Experiment Farm, Rosslyn, Va. } June, IQ20 
1 
2 
3 
4 
Lot No. 
Yield of straw from— 
Yield of grain from— 
Volume of grain from— 
Healthy culms. 
Infected 
culms. 
Healthy culms. 
Infected culms. 
Healthy culms. 
Infected culms. 
, 
Weight. 
Reduction. 
Kernels. 
Galls. 
Kernels. 
Galls. 
Weight. 
Reduction. 
Weight. 
Volume. 
Reduction. 
Volume. 
Gm. 
Gm . 
P. ct. 
Gm. 
Gm. 
P.ct. 
Gm. 
P.ct . 
Cc. 
Cc. 
P. ct. 
Cc. 
P. ct. 
311.9 
178. 6 
43 
141. 7 
49 - 0 
65 
4-5 
8 
190 
70 
63 
15 
18 
269.3 
174.1 
35 
H 3.4 
38.5 
66 
6.0 
13 
150 
55 
63 
15 
21 
212.6 
151- 2 
29 
85.0 
33 -o 
61 
5 - 5 
14 
IIO 
40 
64 
10 
20 
IS 7 - 2 
27.0 
4 - 5 
*4 
45 
20 
3 * 
Average.... 
264. 6 
165-3 
36 
113.4 
36. 9 
64 
5 - i 
12 
150 
52. 5 
63 
is 
22 
It is of especial interest to note that although the average percentages 
of galls are only 12 and 22 per cent by weight and by volume, respec¬ 
tively, the actual average reduction in the yield of kernels from infected 
plants as compared with the yield from uninfected plants is 64 and 63 per 
cent by weight and by volume, respectively. This seems to indicate 
that the percentage by weight or volume of galls in infested grain does 
not truly represent the actual reduction in yield caused by the disease. 
This is shown also in Tables VII and VIII. 
Reports of reduced yields caused by the nematode disease may vary 
widely owing to the different methods used to determine the amount of 
reduction. Percentages of infection may be based on the relative num¬ 
ber of seedlings showing symptoms, the relative number of heads con¬ 
taining galls, or the percentage of galls in the threshed grain. Head 
counts may take into consideration partially infected and totally infected 
heads. The percentage of galls in the threshed grain may be based on 
the relative number, volume, or weight of galls and kernels. In order 
to compare these different methods of taking and recording percentages 
of infection, the data were tabulated from an experiment conducted at 
the Arlington Experiment Farm in the crop year 1919-20, in which the 
relative susceptibility of wheat, rye, emmer, and spelt was studied. 
These percentages are given in Table II. 
