THE EGGPLANT BLIGHT AND FRUIT ROT IN PORTO RICO

Abstract

1. A serious disease of eggplants known in Porto Rico as "lunares de la hoja y tallo" and "podredumhre de la fruta", in the United States of North America as leaf blight, foot-rot, leaf-spot, stem-blight. fruit-rot, eggplant-blight and seedling-stem-blight and in Cuba as "mancha de la hoja" and "enfermedad del tallo" exists in Porto Rico. 2. All varieties of eggplant are more or less equally susceptible under Porto Rican conditions. Color of plant or of fruit has no bearing on susceptibility or resistance. 3. The disease usually brings a loss of 50 per cent or over of the crop. 4. The symptoms of the disease appear on all above-ground parts of the plant. A seedling blight, stem and petiole cankers, spots on leaf blades, fruit stalks and calices and a rotting of the young and mature fruit are produced. 5. The fungus may occur inside the seed. 6. The pathogene responsible for the malady is Phomopsis vexans (Sacc. & Sydow) Harter. 7. Variations of the fungus as have been observed elsewhere do not appear to occur in the fungus in Porto Rico. 8. The size of the pyenidiospores ranges from 5 to 8 microns in length to 1.3 to 3 microns in width. 9. The germ tube of a germinating spore may either enter through a stoma, enter through a wound or force its penetration through the cuticle. 10. Secondary cycles repeatedly occur in fields. 11. The fungus is capable of a saprophytic existence. 12. The prevailing temperature in Porto Rico seems adequate for spore germination. 13. Moisture is a very important factor in outbreaks of the disease. 14. The disease is probably controlled by a three- or four-years rotation. 15. Plants with the symptoms of the disease should be promptly removed from fields. 16. Although seed treatment is beneficial it never completely eliminates the pathogene. 17. Clean seed from unaffected fruit should be demanded. 18. Infested soils should be avoided in preparing seedbeds. 19. Inoculated soils can he rendered safe for seedlings if drenched with a 1-50 formaldehyde solution at the rate of one-half gallon per square foot of soil surface. An application of 4-4-50 Bordeaux mixture is highly beneficial but the formaldehyde treatment is to be preferred. The latter treatment will cost about two-thirds of one cent per seedling. 20. Bordeaux mixture (4-4-50) is quite effective in preventing seedling blight. The treatment is too expensive and therefore inapplicable under ordinary conditions. Bordeaux mixture may be of practical application where labor cost is reduced. The safest and cheapest control measure is to grow healthy seedlings and set them on in uninfested soils.