Many factors contribute to a decline in production of cocoa beans worldwide. Plant diseases such as black pod, witches' broom, and frosty pod rot are major components of the decline in production. Plant pathologists and microbiologists must discover and devise means to reduce disease losses and to save chocolate for the enthusiastic consumers of the world. This review discusses the major disease of cacao and their effect on world production. Accepted for publication 14 June 2001. Published 9 July 2001.
Several commercial formulations of botanical extracts and essential oils are being investigated as possible alternatives to soil fumigation for control of Fusarium wilt diseases. Soil infested with Fusarium oxysporum f. sp. chrysanthemi was treated with 1, 5, and 10% aqueous emulsions of formulated extracts of clove (70% clove oil), neem (90% neem oil), pepper/mustard (chili pepper extract and essential oil of mustard), cassia (extract of cassia tree), and Banrot (a standard fungicide applied at different labeled rates) in separate experiments. Population densities of F. oxysporum f. sp. chrysanthemi were determined at 0 (before treatment), 1, 3, 7, 14, and 21 days after treatment. Treatment of the soil with 5 and 10% aqueous emulsions resulted in significant (P < 0.05) differences among treatment means at each assay date. After 3 days, pepper/mustard, cassia, and clove extracts added as 10% aqueous emulsions reduced the population density of F. oxysporum f. sp. chrysanthemi 99.9, 96.1, and 97.5%, respectively, compared with the untreated control. Neem oil extract increased the population density of F. oxysporum f. sp. chrysanthemi at all concentrations tested. Banrot did not reduce the population density of F. oxysporum f. sp. chrysanthemi in any experiment. In a second, related experiment, soil infested with Fusarium oxysporum f. sp. melonis also was treated with 1, 5, and 10% aqueous emulsions of formulated extracts, incubated in closed plastic bags for 1 week, and planted with muskmelon seeds (cv. Gold Star) in the greenhouse. Treatment of infested soil with 5 and 10% aqueous emulsions of the botanical extracts resulted in differences among treatments after 5 to 6 weeks. The pepper/mustard, cassia, and clove extracts suppressed disease development in repeated experiments (80 to 100% healthy plant stand) compared with the untreated infested soil (<20% stand). The observed reduction in the pathogen population and increased healthy plant stand in the greenhouse indicates that these extracts could have important roles in biologically based management strategies for control of Fusarium wilt diseases.
Lewis, Jack A.; and Chung, Soohee, "Biocontrol agents applied individually and in combination for suppression of soilborne diseases of cucumber" (2005 AbstractThe soilborne pathogens Rhizoctonia solani, Pythium ultimum, and Meloidogyne incognita can cause severe economic losses to field-and greenhouse-grown cucumber. A collection of bacterial isolates and isolates GL3 and GL21 of Trichoderma virens were screened for suppression of diseases caused by these pathogens. T. virens isolates GL3 and GL21 provided the most effective suppression of damping-off caused by R. solani in greenhouse bioassays. Burkholderia ambifaria BC-F, B. cepacia BC-1, and Serratia marcescens N1-14 also provided significant suppression of R. solani relative to the pathogen check in some experiments. T. virens isolates GL3 and GL21 and S. marcescens isolates N1-6, N1-14, and N2-4 provided the most consistent and effective suppression of damping-off of cucumber caused by P. ultimum in growth chamber experiments. No microbial treatment containing individual or combined microbes significantly suppressed populations of M. incognita on cucumber or improved plant vigor in greenhouse bioassays. T. virens GL21 applied as a granular formulation, in combination with B. cepacia BC-1 or B. ambifaria BC-F applied as a seed treatment, significantly improved suppression of damping-off caused by R. solani over individual applications of these microbes in at least one experiment. Treatments combining B. cepacia BC-1, B. ambifaria BC-F, or S. marcescens isolates N1-14 or N2-4 with T. virens GL21 in R. solani biocontrol assays always resulted in plant stands that were similar or greater than treatments containing individual applications of these microbes. B. ambifaria BC-F combined with T. virens GL21 in seed treatments resulted in significantly improved suppression of damping-off caused by P. ultimum in two of three experiments. Populations of T. virens GL3 and GL21 were both substantially reduced after coincubation with B. cepacia BC-1, or S. marcescens isolates N1-14 or N2-4 for 10 to 12 d in cucumber rhizospheres. Populations of T. virens GL21 were slightly reduced after coincubation with B. ambifaria BC-F. Results presented here substantiate other studies reporting enhanced biocontrol performance This article is a U.S. government work, and is not subject to copyright in the United States.with certain combinations of biocontrol agents. These results also indicate that antagonism among combinations of biocontrol agents can vary with the assay system employed. r
Formulated plant extracts and oils were investigated for control of diseases caused by Phytophthora spp. Soil infested with chlamydospores of Phytophthora nicotianae was treated by incorporating 1, 5, and 10% aqueous emulsions of formulations containing clove oil, neem oil, pepper extract and mustard oil, cassia extract, synthetic cinnamon oil, or the fungicide metalaxyl. Population densities of P. nicotianae were determined at 0 (before treatment), 1, 3, 7, 14, and 21 days after treatment. Treatment of the soil with 5 and 10% aqueous emulsions resulted in significant (P < 0.05) differences among treatment mean values at each assay date. After 1 day, population densities were reduced to below the limit of detection (<0.04 CFU/cm3) in soil treated with 10% aqueous emulsions of two pepper extract-mustard oil formulations and two cassia extract formulations, and near the limit of detection for a synthetic cinnamon oil formulation. Over time, populations of P. nicotianae were detected in the assay; however, after 21 days, populations of P. nicotianae in soil treated with one of the pepper extract-mustard oil formulations still were not detected. Formulations of clove oil, another pepper extract-mustard oil combination, the two cassia extracts, and the synthetic cinnamon oil reduced populations 98.4 to 99.9% after 21 days compared with the nontreated control soil. The neem oil formulation and metalaxyl did not reduce pathogen populations at any rate tested. In the greenhouse after 35 days, 10% aqueous emulsions of a pepper extract-mustard oil formulation, a cassia extract, and the synthetic cinnamon oil formulation suppressed disease development in periwinkle 93.0 to 96.7% compared with the nontreated infested soil. The observed reduction in the pathogen population and significantly more healthy plants in the greenhouse indicates that these formulations of plant extracts and oils could have important roles in biologically based management strategies for control of diseases caused by P. nicotianae.
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