GRAND RAPIDS TOMATO DISEASE. 



163 



ADDITIONAL OBSERVATIONS, INOCULATION EXPERIMENTS, AND INFERENCES. 



Inoculations in a hot-house in the fall of 1909 on tomatoes were very successful (plates 

 12 to 15). Subsequently the disease escaped to numerous check tomato plants growing in 

 the same house. It also attacked the spiny Porto Rican weed, which we were cultivating 

 because it had been reported to be immune to the attack of Bacterium solanacearum (p. 182). 

 The outbreak swept the house, much to my chagrin. 



The readiness with which the disease escaped from control indicated easy infection 

 through the stomata of leaves and stems. The bacteria for such infection were known to be 

 available in large numbers owing to the fact that under the influence of this disease the soft 

 stems of the tomato crack open as they shrivel and allow the bacteria to come to the surface, 

 from which the gardener's hose and various insects would afford a ready means of dis- 

 semination. 



Subsequently we obtained experimental proof of stomatal infection. We found that 

 the disease could be produced very readily on tomatoes by making a water suspension of 



young agar cultures and spraying 

 this upon the healthy plants; and 

 sections of very early infections 

 thus obtained showed the bacteria 

 to be located in the substomatic 

 chamber. 



Fig. 72/ 



Fig. 73-t 



Prom these observations and experiments we may conclude that many infections take 

 place above ground and that frequent germicidal sprayings might be expected to hold the 

 disease in check. Anyway, Bordeaux mixture should be tried and also the self-boiled lime- 

 sulphur mixture as made by Scott for the prevention of Monilia on peaches (see Bull. 174, 

 Bureau of Plant Industry, U. S. Department of Agriculture, 1910), and if immediate good 

 results are not obtained the method should not be condemned, since the sprayed plants may 

 have been infected prior to the spraying, the progress of the disease being rather slow. 



The signs of the disease are shown on the plates already mentioned, and the morbid 

 anatomy so far as worked out is given in figs. 72 to 75. 



*Fig. 72. Cross-section of the softer upper part of a tomato stem some months after inoculation with a pure cul- 

 ture of Aplanobacter michiganense and at a distance of several decimeters from the place where the needle entered. For 

 appearance of the plants see plates 12 to 15. Pith in the upper part of the section; a and b, bacterial cavities in the 

 inner phloem similar to the one in the outer phloem but older, and the bacteria and tissue fragments washed out in prep- 

 aration of the section; the lower heavily shaded parts represent collenchyma (all more or less shriveled by alcohol). 

 Slide 539 F 4, upper row, left section. Camera drawing, Zeiss 16 mm. obj., and No. 8 comp. ocular. Inoculation of 1909. 



fFiG. 73. A detail from fig. 72 to show the individual bacteria. The drawing is taken from the margin of the 

 cavity in the outer phloem. Zeiss 2 mm. apochromatic obj., and No. 12 comp. ocular. 



