ANTHRACNOSE OF CUCURBITS. 53 



Table VI. — Laboratory tests of seed inoculated with spores of the anthracnose fungus . 



Date of 

 test, 

 1917. 



Number 

 of seed. 



Medium used. 



Days. 



Result. 



Mar. 14 

 14 



15 



50 

 28 



6 

 6 

 6 



12 

 100+ 



Sterile sand, in damp chamber 



2 per cent dextrose solution, in filter 

 paper. 



29 

 14 



15 

 13 

 17 



17 

 18 



16 out of 45 seedlings diseased. 

 Anthracnose detected on five. 



No anthracnose. 



23 

 23 



23 

 23 



Wet filter paper 



2 per cent dextrose solution, in filter 

 paper. 



Prune decoction, in filter paper 



Wet filter paper, in damp chamber . . . 



1 seedling diseased at heel. 

 No anthracnose. 



Do. 

 Do. 



As a result of the difficulties encountered and negative results 

 secured in the endeavor to prove by laboratory methods the presence 

 of the anthracnose fungus on commercial seed, the problem was ap- 

 proached in another way. 



FIELD TESTS WITH DISINFECTED SEED. 



Certain theoretical considerations form the basis of this method 

 of attack. Since observation indicated that the number of original 

 centers per acre was usually rather low, ranging perhaps from 1 to 10, 

 and since about 2 pounds, or approximately 70,000 seeds, are used 

 per acre, it was to be assumed on the basis of seed carriage of disease 

 that not more than 1 to 10 seeds out of 70,000 were acting as suc- 

 cessful bearers of the disease. In view of this possibility, the failure 

 of the laboratory tests might be attributed in part to the relatively 

 small numbers of seeds tested. 



To obtain a test with larger numbers of seeds, recourse to field con- 

 ditions was necessary. It was obvious that if the fungus could be 

 eliminated by surface sterilization of .the seed, the appearance of the 

 disease in a new field planted with such seed should be prevented, 

 while in a field planted with untreated seed the disease would nor- 

 mally be expected were the fungus present on the seed. 



As to the character and effect of various seed treatments, more 

 will be presented later. Suffice it to state here that the surfaces of 

 seeds immersed in mercuric chlorid of a strength of 1 to 1,000 for 5 

 minutes were found by agar-plate tests to be sterile. With the other 

 disinfectants employed, the effectiveness against the anthracnose 

 fungus was assumed. Two classes of tests were made in the season 

 of 1917, one limited to a few fields at Madison, the other being more 

 extensive. 



At Madison a mixture of 1916 Ohio seed previously tested with a 

 new consignment from the same source was tested in four well- 

 separated one-half acre fields on soil not previously in cucumbers or 

 melons. In one field untreated seed was planted, while in the others 

 seed treated as shown in Table VII was used. By planting double 



