BACTERIAL CANKER OF TOMATO: TRANSMISSION 219 



Agriculture hothouses and infected various check tomato plants 

 and also a bed of West Indian plants {Solanum mammosum) 

 said to be resistant to Bacterium solanacearum. This unwelcome 

 infection was attributed to spatterings from the gardener's 

 hose. I first called attention to this method of dissemination 

 in 1914. The experiences of growers in New York and Massa- 

 chusetts show that it is capable of doing much damage to hot- 

 house tomatoes. 



Host Plants. — It is very important to determine whether 

 this parasite has other hosts than the tomato. I believe it 

 occurs also on the potato but the evidence is not yet conclusive. 



In the winter of 1918-19 I received potatoes from Berk- 

 shire Co., Mass., said to be fair samples of a great many occurring 

 in that locality. These tubers were sound externally but the 

 outer one-half inch or more of their flesh was mottled with 

 numerous brown spots, forked lines and streaks (Fig. 161). On 

 studying sections under the microscope, no distinct lesions 

 were observed but foci of bacteria were found in the center of 

 some of the spots. In all the tubers I examined, the stem end of 

 the tuber was always badly diseased, but often the eye-end 

 was free (Fig. 162). When the flesh of the tuber was examined 

 in thin section (1-3 mm.) by transmitted light, the brown spots 

 and streaks were seen to be surrounded by a narrow clear zone 

 indicating disappearance of the starch in the surrounding 

 tissues (Fig. 163) which was confirmed by tests with iodine. 

 Several organisms were cultivated out on potato. Some made 

 a pale whitish slime at first, becoming distinctly yellow, but in 

 other cases pure white cultures were obtained, and in many 

 instances nothing whatever. Inoculation tests on tomato 

 and potato gave nothing definite. 



This disease was not discovered by the planters in the field 

 but during the winter in the stored tubers (variety, Green 

 Mountain). This new disease has received the name of "Net- 

 necrosis." By some it has been ascribed to frost injuries, but 

 I cannot think the phenomena as it occurred in Massachusetts 

 in the winter of 1918-1919, and as shown on the accompany- 

 ing plates, w^as due to freezing. When the plates were made 

 I believed the disease due, probably, to bacteria, but now I 



