STUDIES ON THE BACTERIAL WILT OF THE SOLANACEAE IN PORTO RICO

Abstract

1. A. bacterial disease of solanaceous vegetable crops has been prevalent in Porto Rico for many years. 2. The disease affects tomato, potato, eggplant, and pepper; Solanum torvum, S. nigrum and zinnias become infected occasionally, while tobacco appears to be immune. 3. All imported varieties of tomato, pepper, and eggplant are more or less susceptible. The Marglobe and the Marvelosa tomatoes and the Bull Nose, World beater, Chinese Giant, Ruby King, Crimson Giant and Improved Ruby King peppers are very resistant. The most resistant of the imported eggplants is the New Orleans Market. The most susceptible of all suscepts used are the Ponderosa tomato, the Early Giant and Ruby Giant pepper's, and the Black Beauty eggplant. Four varieties of potato were found susceptible. 4. Peppers are more resistant than either eggplants or tomatoes. 5. Native varieties of eggplant are more resistant than the imported sorts; but all native peppers and tomatoes are very susceptible. Hot peppers proved to be more resistant than the sweet peppers. 6. The disease is very severe on tomatoes and to a less extent on eggplants, at the seedling stage. 7. Normally resistant varieties of eggplant may contract the disease if artificially inoculated. 8. Some diseased plants of the resistant eggplant recovered from the disease. 9. The symptoms of the disease are characterized as a yellowing and withering of the tender shoots and leaves and finally a complete wilting of the affected plant. Sometimes lesions having the appearance produced by scalding water or scorched by strong sunlight are evident. Cankers are formed occasionally in tomatoes. Histologic symptoms consist of a browning of the vascular bundles. 10. The pathogen is culturally indentical with Phytomonas solanaceara (E. F . S.) Com S. A. B. bacterium solanacearum E. F . S. or very similar to it. In cross-inoculation studies it is also similar to it, but is unable to infect tobacco. We are of the opinion that it is only a strain of that pathogen. 11. The organism loses it virulence very readily on most artificial culture media. 12. Successful inoculations with the pathogen in culture were obtained when the inoculum was used directly from the original isolation on the poured plate. Inoculations with the bacterial ooze obtained in more or less uncontaminated condition from the vascular bundles of diseased plants scarcely ever failed. 13. Natural infection occurs through wounds in the leaves and roots. 14. The pathogen may be disseminated by the green beetle, Diabrotica graminea Baly. 15. The pathogen seems to be harbored in manure, plant remains, etc., and appears to exist in soils for a number of year's. 16. It is believed that the first appearance of the disease coincides with periods of continued rainfall followed by periods of drought. 17. The production of resistant strains of the various crops seems to offer a logical means of control. Breeding work in the eggplant is in progress. 18. Grafting of susceptible varieties on Solanum Torvum only eliminates the chances of root infection. The writer wishes to express his gratitude to Hon. C. E. Chardón, former Commissioner of Agriculture and Labor of Porto Rico and to Mr. F. A. López Domínguez, formerly Director of the Insular Experiment Station, who encouraged and supported the work on this problem. He is also greatly indebted to Dr. Mel. T. Cook, Plant Pathologist of the Insular Experiment Station, for his helpful advice and criticisms and to Professors H. H. Whetzel, M. F. Barrus and W. H. Burkholder for help in the preparation of the manuscript.