Mayis, igis Seedling Diseascs of Sugav Beets 145 



often observed in commercial fields, and it is probably safe to say 

 that, under advantageous conditions of climate and cultivation, 75 

 per cent of the beets attacked by Phoma betae are not killed, but throw 

 off the parasite sufficiently to make a good growth while continuing to 

 carry the fungus in a dormant condition upon the crown. When the 

 vitality of the host is sufficiently reduced, the parasite may become active 

 again and develop either in the root, where it causes a black rot, or on 

 the aerial portions of the plant, where it causes a spot disease, which, 

 while it does not injure the host to an appreciable extent, enables the 

 fungus to infect the seed growing on mother plants. The rot is, of course, 

 more serious to the plants attacked. Cases of this so-called heart-rot in 

 the field have been very destructive at times in certain sections of 

 Europe and are not infrequent in America. Important instances of 

 its occurrence in Michigan, Wisconsin, and Colorado, and a less serious 

 case in New York, have come to the writer's attention. Material from 

 the three States first mentioned was available for study. The fungus 

 was easily secured in pure culture from the beets that were partially 

 decayed by the black rot typical of the disease (PI. XVIII, fig. i). 

 Many roots presented unmistakable evidence of having been diseased 

 in the seedling stage. In some cases the original taproot had been de- 

 stroyed, and only a knob of tissue just below the crown had survived. 



Additional evidence that the fungus is capable of living upon its host 

 for a long time in an inconspicuous and apparently harmless form until 

 those conditions appear which are favorable to its development is readily 

 found upon examination of beets in storage or those which have been 

 kept over for seed purposes. Such examination in the spring has never 

 failed to reveal the presence of the fungus. Sometimes the entire root 

 is destroyed, but more frequently beets that are apparently healthy may 

 be found to show black spots in certain sections in or near their vascular 

 tissue, especially in the top of the crown. These areas usually develop 

 longitudinally and are frequently confined to the vicinity of a single 

 vascular bundle (Pi. XIX). When the conditions of storage have been 

 unfavorable, the rot may assume an epidemic form and lead to the total 

 destruction of roots which were apparently healthy and sound when 

 placed in storage. 



INOCULATION EXPERIMENTS ON GROWING BEETS 



Evidence that the infection takes place only in the seedling stage or 

 through the leaves in old age is found in the results of inoculation experi- 

 ments made with cultures of Phoma betae. In August, 191 2, 100 ap- 

 parently healthy beets growing in the field at Madison, Wis., were 

 inoculated. A portion of the infections were made directly upon the 

 uninjured crown with vegetative cultures upon beet blocks. Other 

 inoculations were made through wounds near the surface of the soil and 



