34 



BULLETIN 828, U. S. DEPARTMENT OF AGRICULTURE. 



all, in 15 to 20 days after inoculation (fig. 8). However, in 26 out 



of the 51 sets of inoculations the plants all recovered after partial 



wilting. It will be noted that the first signs of the disease and wilting 



of the first leaf were only a little slower in appearing than in cucumber, 



but in general a much longer time elapsed before the whole plant 



became involved. A far greater percentage of recovery was exhibited 



than in cucumber. 



Field records during 1916 in the spray plat at East Marion, Long 



Island (fig. 1, Field Ila), showed that among the cucumbers where 



wilting of the first leaves appeared on July 12 the larger number of 



plants had completely succumbed six days later (July 18). The 



vines at this time were 1 to 2 feet in length, which was approximately 



the size of those used 

 30i — 



FIRSTSI6NS OFWILT 



WILT OF FIRST LEAF 



WHOLE PLANT WILTED 



co 



o20 



<o 



»— 



CO 



I— 



U- 



°|0 



Cer 

 LU 



CO 



18 



*** • 



10 



in the greenhouse in- 

 oculation tests above 

 noted, and it will be 

 seen at once that the 

 period between the 

 wilting of the first 

 leaves and the total 

 wilting of the plant 

 corresponds very 

 closely under the field 

 conditions and the 

 greenhouse con- 

 ditions. 



Of the plants which 

 showed wilting of the 

 first leaves on July 1 8 

 the larger number had completely wilted 1 1 days later, while of those 

 with first wilt on July 29 the larger number lived for 1 7 days longer. 

 Complete records of later infections could not be obtained, on ac- 

 count of the appearance of downy mildew. 



As would be expected, the larger the plant the longer the period of 

 time elapsing between initial and total wilting. However, the two 

 are not directly proportional, since in the older plants the absolute 

 progress of the disease is slowed down through some relation to the 

 condition of senility in the host. (Cf. pp. 31 and 32.) 



DISTRIBUTION OF BACTERIAL WILT. 



Bacterial wilt of cucurbits was reported by Dr. Erwin F. Smith x 

 as occurring (fig. 9) in Canada, Massachusetts, Vermont (?), Rhode 

 Island, Connecticut, New York, New Jersey, Delaware, Maryland, 

 District of Columbia, Virginia, West Virginia, Pennsylvania, Ken- 



w At 10 20 30 



A/umber of pays 



Fig. 8. — Diagram showing the progress of wilt in 51 inoculation tests 

 on squash (mostly the W"hite Bush Scallop variety), with two or 

 more plants to a test and in all using 21 different isolations of 

 Bacillus tracheiphilus. 



i Op. cit., p. 209-211. 



