May 15. 191S Seedling Diseases of Sugar Beets 155 



of the diseased seedlings examined have yielded cultures of Rhizoctonia. 

 The fungus is the cause of a very destructive crown- rot in the West 

 (PI. XX, XXI, and XXII), where it frequently becomes epidemic. It is 

 not uncommon to see entire fields of 50 or 100 acres practically destroyed 

 in August by root-rot, of which there is no evidence earlier in the season 

 (PI. XXI, fig. i). This form of rot is seen only occasionally in the more 

 eastern beet-growing districts, where it appears to be of no economic 

 importance. 



CONDITIONS INFLUENCING INFECTION 



The controlling influences in the distribution of the Rhizoctonia dis- 

 eases of the beet may conceivably be associated with the unequal dis- 

 tribution of the fungus or with differences in climate or in soil, or \nth 

 any combination of these. Some light has been shed upon this point 

 in the course of the inoculation experiments on growing beets. Field 

 inoculations were first made in Wisconsin, using cultures obtained from 

 Colorado and Kansas. The first series was made on August 21, 191 2, 

 by placing portions of mycelium upon agar among the heart leaves of 

 beets in the field. The inoculations were made just at dark, and the beet 

 leaves were moistened w4th water from a sprinkler, in imitation of a 

 heavy dew. The morning of the 2 2d was cloudy, and a very little rain 

 fell. The weather of the next few days was dry and hot. Examination 

 a few days later showed that infection had occurred in all except one of 

 the 29 beets inoculated. The disease, however, failed to make the 

 progress typical of western conditions. At the time of harvest, October 

 23, one beet showed no evidence of infection even at the point where 

 inoculation was made and where the original dried culture was clearly 

 seen. Six showed no injury other than slight lesions on petioles such 

 as shown in Plate XXI, figure 2. Five showed old lesions on the crown, 

 but they had entirely recovered. Eleven beets showed so slight evidence 

 of decay that it was observed only on close examination. Five showed 

 clearly defined decayed spots, but even these were restricted in area. 

 One had entirely lost its original crown of leaves, but had formed scar 

 tissue and had developed new leaves from the meristem at the sides. 

 (PI. XXII, fig. I .) This was the only beet which had been injured for the 

 commercial market, unless it might be that the sugar content of the 

 others had been lowered. 



A second set of inoculations were made on August 28. In this 

 instance 40 beets were inoculated by placing on the crown of each a 

 portion of Rhizoctonia myceHum growing on a sterilized beet block. 

 The results were very much Uke those of the first series. While the inoc- 

 ulations took in every case, most of the beets outgrew the infection. 

 Five beets were sufficiently injured to be unfit for market, but only one 

 was killed. In these cases of serious infection the progress of the dis- 

 ease corresponds closely to that seen in the West, although it was far 



