Angular Leaf-Spot of Cucumbers 



475 



Some weeks later the experiment with copper sulphate was repeated. 

 To liter quantities of distilled water in Jena flasks, chemically pure copper 

 sulphate was added so as to obtain the following dilutions: i to 50,000; 

 I to 100,000; and I to 500,000. Some hours after full solution, 10 c. c. 

 of each dilution were pipetted into sterile test tubes and to each was 

 added a 3-mm. loop from a heavily clouded water suspension made from 

 a 24-hour agar slant culture. From each of these tubes three plates 

 were then poured at the end of 5 minutes, and again three more at the 

 end of 10 minutes. As a check, a 3-mm. loop of the cloudy bacterial 

 suspension was added to 10 c. c. of distilled water and from this tube 

 three plates were also poured. The agar for the first set of poured plates 

 was seeded with a 3-mm. loop from the dilution tube, that for the second 

 set with a 2-mm. loop, and that for the third set with a needle dipped 

 one-half inch into the fluid. The results in colonies are given in Table II, 

 the counts being made on the sixth day. 



SUMMARY 



(i) The angular leaf -spot of cucumbers is a widespread disease occur- 

 ring in many of the Eastern and Middle Western States. 



(2) It is characterized by angular brown spots which tear or drop out 

 when dry, giving to the leaves a ragged appearance. In the early stages 

 a bacterial exudate collects in drops on the lower surface during the 

 night and dries whitish. 



(3) Young stems and petioles may become soft-rotted or cracked open. 



(4) A virulent outbreak often materially reduces the crop by destroy- 

 ing the needed active leaf surface. 



(5) The spot is caused by Bacterium lachrymans, n. sp., which enters 

 through stomata, no wounds being necessary. This organism is quite 

 diflterent from the one described by Burger ^ in his papers on cucum- 

 ber rot. No direct connection has been found between the leaf-spot 

 and the soft-rots of the fruit. 



(6) Considering the results obtained in the laboratory with copper 

 sulphate, it would seem that Bordeaux mixture properly applied is the 

 remedy for this disease. Thorough field tests with it should at least be 

 undertaken where the disease is troublesome. 



' Burger. O. F. Op. cit. 



