120 abstracts: phytopathology 



plants in the same year, occurring in widely separated areas — the nas- 

 turtium leaf-spot in Virginia, and the sugar-beet leaf-spot in Utah. 



The cause of the disease, a bacterium, was isolated from each host, 

 and the organism isolated was proved up in each case by means of in- 

 oculations. As it was supposed that two distinct diseases were being 

 dealt with, work was carried on independently for two years, when, 

 through comparison of cultural and morphological tests and by cross- 

 inoculations, it was proved that the organisms causing the leaf-spot 

 disease on both hosts were identical. The same organism also pro- 

 duces spots on bean leaves and pods, also on leaves of lettuce, pepper, 

 and eggplant. 



The organism is called Bacterium aptatum. It belongs to the green 

 fluorescent group of bacteria, and has been shown to be different from 

 Bacterium xanthochlorum , an organism in this group pathogenic 

 to potato ; and from Pseudomonas tenuis, which has been given the 

 same group number in the descriptive chart of the Society of American 

 Bacteriologists. It is also different from Bacterium phaseoU, although 

 both organisms produce the spotting of bean leaves and pods. 



N. A. B. 



PHYTOPATHOLOGY.— T'/ie/oo^-ro^ of the sweet potato. L. L. Harter. 

 Journal of Agricultural Research 1: 251-273. 1913. 

 The foot-rot, a new disease of the sweet potato, is caused by the fungus 

 Plenodomus destruens. It was found in Mrginia for the first time during 

 the summer of 1912 and caused extensive damage that season and in 

 1913. In some fields as much as 95 per cent of the plants were killed. 

 The organism kills the plants primarily by. the destruction of the cor- 

 tex of the stem, although occasionally it may be found on the vines 

 several feet from the hill. Numerous inoculations have proven the 

 parasitism of this fungus. Experiments have shown that it will grow 

 from diseased roots into the slips produced therefrom; also from dis- 

 eased slips into the roots. The fungus lives over the winter on dead 

 vines in the field and probably on the roots used for seed. The disease 

 occurs in the hot bed, so that it is likely that the sale or exchange of 

 slips and seed potatoes is largely responsible for its distribution. Sani- 

 tary methods and careful selection of only sound healthy potatoes for 

 seed are recommended as means of control. L. L. H. 



