PATHOGENICITY OF H. SATIVUM 39 



Many factors that are difficult to control enter into field experiments 

 and complicate the results in such a way as to make them indicative 

 rather than conclusive. In these experiments foot- and root-rot de- 

 veloped slightly more vigorously on Lion barley in the wettest soil and 

 on the two varieties of wheat in the driest soil. This may be only a 

 confirmation of the earlier greenhouse experience that root infection 

 tends to be worse under either extremely dry or extremely wet conditions. 



INFLUENCE OF SOIL FERTILITY 



The effect of soil fertilization on the development of foot- and root- 

 rot caused by H. sativum was studied in field plots on Lion and Man- 

 churia barley, and on Marquis and Bluestem wheat. Potassium and 

 nitrogen in the form of muriate of potash and nitrate of soda were 

 added to square-rod plots at the rate of 600 and 300 pounds of fertilizer 

 to the acre. Treble superphosphate was added at the rate of 200 and 

 100 pounds. These fertilizers were so applied that there were plots 

 with a heavy and a light application of each alone and in combination 

 with a heavy and light application of each of the others, except that 

 there were no combinations of nitrogen and potassium. In addition to 

 these, complete fertilizer was applied at the rate of 600 and 300 pounds 

 and manure at the rate of 20 tons and 10 tons per acre. Unfertilized 

 plots were left as checks. All the plots were run in duplicate, one series 

 planted with wheat and one with barley. The north half of the wheat 

 plots was planted with Marquis, the south half with Bluestem, the 

 north half of the barley plots with Lion, the south half with Manchuria. 



Several days before planting, H. sativum grown on sterilized wheat 

 seed was applied on the surface of the soil at the rate of one half gallon 

 of the culture to the square rod. The plots were seeded with a field 

 drill, wheat at the rate of 90 pounds to the acre, and barley at the rate 

 of 86 pounds. This is the normal rate of seeding for this section of 

 the country. 



Practically no seedling blight developed on any of the plots. Leaf 

 lesions and foot-rot first appeared on the barley during the second and 

 third weeks, and soon after lesions developed also on the wheat. 



There was considerable difference in the vigor and height of plants 

 on the different plots in response to the different fertilizers. During 

 the latter part of the season, there were differences in the amount of 

 lodging on the various plots. Final data on the amount of foot- and 

 root-rot were taken just previous to the ripening of the grain. In order 

 to obtain an approximately quantitative expression for the amount of 

 infection in each plot, 50 plants were selected from each half square 

 rod, 10 from eacfi corner, two feet in from the margins, and 10 from 

 the center of the plot. For each of these plants the following data 



