866 
Journal of Agricultural Research 
Vol. XXVII, No. ir 
Table III shows that, as in the previous year, scab infections were more 
than a hundred per cent greater where wheat followed com than where 
wheat followed other crops. It also shows that infection is much worse 
when all the cornstalks are left on the field than when nearly all of them 
are removed. It must be borne in mind, however, that the corn stubbles 
were left exposed and that they were thus an important factor in in¬ 
creasing the disease in fields 610, 133, and 109, as compared with fields 
611, 132, and 107, respectively. 
The study of the influence of the previous crop on the development 
of wheat scab had shown that the abundant development of perithecia 
on the old cornstalks determined to a large measure the relative amount 
of wheat scab. It was important, therefore, to determine the extent 
to which these perithecia would develop on stalks of relatively resistant 
strains of com. Such strains of corn were available, as considerable 
work had been done by J. R. Holbert and his associates (10, 12 4 ) in the 
breeding and selection of strains resistant to the root and stalk rots. 
In the fall of 1920 an experiment was planned with this corn to deter¬ 
mine the extent to which the perithecia of Gibberella would develop on 
stalks from corn showing considerable resistance to the root- and stalk- 
rots. Stalks were obtained from three different selections: (1) The most 
disease-resistant obtainable; (2) comparatively disease-resistant; and 
(3) disease-susceptible. A large bundle of each kind was taken to a 
wheat field in the fall after the wheat had been sown and each bundle 
was scattered sufficiently to insure that each stalk came in contact with 
the soil. Just prior to wheat harvest the following year the cornstalks 
were collected and taken to the laboratory to determine the relative 
abundance of Gibberella perithecia on those from each selection. Esti¬ 
mates were made on representative portions from each stalk, each portion 
including a node and an internode. To establish standards, five pieces 
were selected with perithecia ranging in abundance from few to very 
numerous. On the piece where the perithecia were very numerous they 
covered about half the surface. Therefore, this sample was classed as 
50 per cent covered. The piece having only a few perithecia was rated 
as 10 per cent, as this was about the proportion of surface covered. The 
other three portions were intermediate, differing by about 10 per cent, 
thus making the series 10, 20, 30, 40, and 50 per cent covered. These 
samples were used as standards in estimating the percentages of surface 
covered on all the portions of each stalk. These percentages were then 
averaged to get the average percentage for each stalk. The results are 
given in Table IV. 
It will be noticed that there were not so many perithecia on stalks of 
the resistant selections. Nevertheless there were sufficient perithecia 
even on these to cause an epidemic of wheat scab under favorable con¬ 
ditions. These corn plants were resistant to fungus invasion during 
their active growing and maturing period, but after maturity and death 
of the tissues any com plant is readily invaded by many soil-borne, 
facultative parasites, and among these Gibberella saubinetii is very com¬ 
mon. It seems evident, therefore, that growing only disease-resistant 
com will not aid materially in avoiding higher percentages of scab in¬ 
fection when wheat follows a crop of com. 
4 Holbert, J. R., and others, physical characters op the corn ear in relation to disease resist¬ 
ance and yield. Ill. Agr. Exp. Sta. (In press.) 
