Some Fungous and Bacterial Diseases of tKe Potato 



Douglas 'Weir, B.S A... Biological Department, Macdonald College 



(Continued from last issue) 



PROF. L. R. JONES, of the Vermont 

 Agricultural College, Burlington, 

 has recently published the results of 

 some interesting experiments with the 

 fungus rot (18th report, Vermont Agri- 

 cultural Experiment Station) and as the 

 climatic conditions of Vermont and 



"Little Potatoes," Rhizoctonia 



ormed on stem or branches above the point of injury. 

 I rom Bulletin No. 70. Colorado Ex[>erimcnt Station.) 



yucbec are similar, his experiments may 

 I)crhaps deserve our attention. 



Professor Jones selected Delaware 

 jwtatoes which were planted in the early 

 part of June in a heavy, moist, clay- 

 loam. On August 2, the surface of 

 •he soil immediately under and sur- 

 "lunding the potato plants was sprayed, 

 ' ith Bordeaux mixture (copper sulphate 

 lbs., lime 4 lbs., water 40 gals.), care 

 being taken lo prevent the mixture fall 

 ing on the foliage. Spraying was re 

 peated on August 18, and up to this 

 ime no phytophthora bhght had been 

 (■en. Soon after the second spraying, 

 however, the blight appeared and de- 

 veloped rapidly throughout the rows 

 luring September. The final spraying 

 '.as given on August 28, so that after 

 jjraying had been concluded, one-half 

 he plants had been treated three times 

 11(1 the other half remained untreated 

 lor comparison. . As September was a 

 wet. warm month, the blight developed 



profusely and the results of the experi- 

 ment were consequently well marked. 

 The following are the yields recorded in 

 pounds: Soil sprayed — sound tubers, 

 60.2; rotten tubers, 12.5. Soil un- 

 spraved — sound tubers, 13.5; rotten 

 tubers, 57.9. 



DISCUSSION OF RESULTS 



Professor Jones writes: "The results 

 of the two trials arc in general agree- 

 ment in showing, not only that the 

 disease passes from leaf to tuber, but 

 that the main channel at least is through 

 the soil rather than through the stem." 

 The professor, in concluding, informs 

 us that the rot appeared in spite of the 

 spraying, and in view of this fact all the 

 infection cannot be explained by the 

 sporulation from the leaves or the pass- 

 ing of the fungus threads through the 

 stem; but undoubtedly some spread 

 occurs from tuber to tuber in the soil. 

 Professor Jones fails, however, to state 

 whether the potato sets used in his ex- 

 periments were free from blight when 

 planted. Some of the questions that 

 would naturally present themselves to 

 the potato grower in this connection are : 



tribute the consequent infection to 

 spores, blown from diseased plants, 

 effecting an entrance through tuber or 

 leaf, or to spores from decayed tubers 

 or stems already in the ground. 



If the sets were gathered at random, 

 some would undoubtedly be infected. 

 If, however, they were known to actually 

 contain the dormant hybemating my- 

 celium of the phytophthora blight at the 

 time of planting, we would have a 

 clearer basis to work on and the results 

 of the experiment would be more com- 

 prehensive. At all events. Professor 

 Jones proves that, after the plant is in- 

 fected the further spread of the fungus 

 is largely by the leaf spores (conidia) 

 falling to the ground and being carried 

 by rains to the tubers as previously 

 mentioned. 



AN EXPERIMENT 



Another experiment conducted under 

 the direction of Professor Jones, with a 

 view to ascertaining whether the fungus 

 spreads from tuber to tuber in the soil, 

 proved this to be the case. Professor 

 Jones states that "upon digging at dif- 

 ferent times and places during the last 



Tomatoes Grown in Alberta — See Next Page 



(a) Were the potato sets experi- 

 mented with free from phytophthora 

 bUght? 



{b) Were they gathered at random? 



(c) Did they actually contain the 

 hybernating mycelium and show the 

 characteristic markings? 



If the sets were free from the fungus 

 when planted, we would naturally at- 



half of the month (Sept., 1905), the 

 fungus (phytophthora) was frequently 

 found growing in tufts from the surface 

 of decaying tubers ; and such tufts were 

 always richly covered with spores. 

 Moreover, the soil conditions were favor- 

 able for their develojjment and for 

 further infection of tubers, as was 

 shown by the fact that some of these 



