﻿SYMPTOMS OF WHEAT ROSETTE. 3 



on soil of extremely high infestation appeared to be in a perfed stat< 

 of health during; the autumn. While certain fungi infect the outer 

 tissues of the subterranean tiller parts and the subcrown internode, 8 

 the general field appearance of the plants was far better than that di 

 varieties not known to develop wheat rosette. 



Plant symptoms. — While the characteristic plant symptoms of i he 

 disease do not develop in the fall, close observations and tiller counts 

 seem to indicate that the excessive development of tillers, which is 

 so characteristic of the disease in the spring, commences to a certain 

 extent in the autumn. However, since other important symptoms are 

 not associated with this fall condition, its importance as a fall symp- 

 tom and as an indicator of the development of the disease in the 

 spring is still a question. 



SPRING PERIOD. 



Field symptoms. — -The first positive indications of the disease 

 become evident early in the spring after the growth of the healthy 

 plants is well started. In the fields but slightly infested, distinct 

 patches of badly dwarfed plants show here and there without regard 

 to the type or condition of the soil (PI. I). Such patches may vary 

 in size from those containing but a few diseased plants to areas 

 many feet in diameter. Often these patches are almost circular in 

 shape, while others are irregular. It is not uncommon to find dis- 

 eased plants occurring singly intermixed with healthy plants. In 

 cases where spotting occurs, the edges of such spots are usually more 

 sharply defined than the margins of spots caused by unfavorable soil 

 conditions, especially poor 1 drainage. In the rosette-spotted areas 

 most of the plants are diseased and therefore stunted right up to 

 the edge of the spot. In spots caused by local unfavorable soil condi- 

 tions all the plants usually decrease in height gradually from the 

 edge toward the center. 



In fields more severely infested it is not uncommon to find a large 

 proportion or in some cases all of the field involved. In such cases 

 most of the plants may be affected. There is no case on record, how- 

 ever, where all plants in a large area have developed the disease. 

 Investigations have shown that apparently there are resistant strains 

 in the most susceptible varieties. 



A striking characteristic of fields affected by the disease in the 

 early spring is the comparative freedom from blank spaces or areas 

 due to dead plants. Practically all plants are intact, even though 

 diseased. Later in the spring, however, under certain conditions such 

 plants may die. During seasons of heavy rainfall diseased, plants 

 may be washed out of the soil, causing blank areas in the field, but 

 this condition is rather unusual. 



Plant symptoms. — Plants affected by rosette remain dormant in 

 the spring after healthy plants commence their spring growth. The 

 fall tillers of the diseased plants usually do not " shoot," or if they do 

 the process is delayed and of short duration. The leaves of diseased 

 plants are dark blue-green in color. They are rather broad and stiff. 

 Thus far, no parasites or external lesions have been found consistently 

 associated with the vital tissues of diseased plants during this period. 



2 The term subcrown internode is used to designate the elongated region which under 

 certain conditions develops between the seed and "the crown of the plant. 



