THE BLACK-SHANK OF TOBACCO IN PORTO RICO

Abstract

1. A disease known in Porto Rico as "pata-prieta" and probably the same as the black-shank from the Southern United States and the "Lanas" or "bibit" of the Dutch East Indies has been destructive in Porto Rico during the last few year's on tobacco. 2. The pathogene which is responsible for this disease may also attack Ricinus communis, potato plants, pepper, tomato and eggplant seedlings under certain conditions in Porto Rico. 3. A non-commercial variety of tobacco (mammoth-type) proved to be the most susceptible of all varieties to the malady. Of the two important commercial cigar-wrapper varietie's in Porto Rico, one was found to be very susceptible and the other very resistant; while all the cigar-filler varieties were slightly susceptible. New strains of a Porto Rican variety of cigar-wrapper tobacco have exhibited a high resistance. 4. First generation populations of crosses between a very susceptible variety and other susceptible or slightly resistant types were very snsceptible to the attacks of the pathogene. On the other hand, those crosses of resistant varieties with susceptible ones were more resistant than the susceptible parent. 5. The symptoms of the disease are produced on plants of all ages. A bed rot and seedling blight, a rotting of transplants, a blackening of the basal parts of the stems of plants of all ages and a leaf spot on big plants, are the most important morphological symptoms. 6. The causal organism also produces a severe rotting of seedlings in the seedbeds. 7. The black-shank pathogene was the cause of a disease of transplants called "hinchado" (water-soaked or swollen). 8. The causal pathogene is here given as Phytophthora nicotianae Breda de Haan. The organism from Porto Rico appears to be morphologically different from that of Florida. The Porto Rican fungus is, therefore, considered a different strain. The Porto Rico and the Florida strains were not compared culturally or morphologically with the strain from Sumatra. 9. The Florida strain does not differ from the Porto Rican strain essentially in cultural characteristics or in pathogenicity. 10. The size of chlamydospores is of no value in the separation of the strains. Use was made only of the size of sporangia. 11. Moisture is a dominating factor in outbreaks of damping-off caused by the black-shank pathogene. 12. Irrigation water is an important agent in the transportation of the pathogene from one field to the other. 13. P. nicotianae lives in the soil as a saprophyte on plant debris, old tobacco stems or manure. 14. As control measures are recommended: (a) the removal of diseased individuals, (b) the rigid selection of seedlings before setting out in the field, (c) the dipping of healthy seedling's obtained from a diseased bed in a 4-4-50 or a 5-5-50 Bordeaux mixture before transplanting, (d) the selection and breeding of resistant varieties. 15. The treatment of the soil with Bordeaux mixture was not effective in preventing the disease.