Relationship of inoculum densities of Phytophthora spp. in soil to cacao roots disease
Responses of cacao seedlings to infection by defined levels and forms of inoculum of P. capsici, P. citrophthora, P. heveae, P. megakarya and P. palmivora in soil were determined. Inoculations were done with 100, 250 or 500 chlamydospores or oospores per gram of soil or 10 exponent 5, 5 x 10 exponent 5 or 10 exponent 6 zoospores per plant. Cacao seedlings of a susceptible and a tolerant cultivar were used and at least 10 plants of each of the cultivars were inoculated. All of the experiments were performed twice with each form of inoculum. The plants were harvested eight weeks after planting and their root systems plated on PARPH. Wilted plants were also recorded. Infection occurred in roots of both susceptible and tolerant cultivars using all forms of inoculum. Levels of infection and severity of disease varied with the species of Phytophthora, inoculum concentration and cultivar tested. Damage was greatest at highest inoculum levels but, mortality was caused only by P. citrophthora and P. palmivora. These two species also caused more root damage than other species. Plants that do not show external symptoms may function as reservoirs of inoculum.
| Main Authors: | , , |
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| Format: | biblioteca |
| Published: |
Jul
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| Subjects: | THEOBROMA CACAO, PLANTULAS, PHYTOPHTHORA CAPSICI, PHYTOPHTHORA CITROPHTHORA, PHYTOPHTHORA HEVEAE, PHYTOPHTHORA MEGAKARYA, PHYTOPHTHORA PALMIVORA, ENFERMEDADES FUNGOSAS, INOCULACION, BRASIL, |
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| Summary: | Responses of cacao seedlings to infection by defined levels and forms of inoculum of P. capsici, P. citrophthora, P. heveae, P. megakarya and P. palmivora in soil were determined. Inoculations were done with 100, 250 or 500 chlamydospores or oospores per gram of soil or 10 exponent 5, 5 x 10 exponent 5 or 10 exponent 6 zoospores per plant. Cacao seedlings of a susceptible and a tolerant cultivar were used and at least 10 plants of each of the cultivars were inoculated. All of the experiments were performed twice with each form of inoculum. The plants were harvested eight weeks after planting and their root systems plated on PARPH. Wilted plants were also recorded. Infection occurred in roots of both susceptible and tolerant cultivars using all forms of inoculum. Levels of infection and severity of disease varied with the species of Phytophthora, inoculum concentration and cultivar tested. Damage was greatest at highest inoculum levels but, mortality was caused only by P. citrophthora and P. palmivora. These two species also caused more root damage than other species. Plants that do not show external symptoms may function as reservoirs of inoculum. |
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