The search for Phytophthora pod rot resistance and escape at the Cocoa Research Institute of Nigeria during the 1960s
The research effort towards economic control of Phytophthora pod rot (Ppr) disease carried out in the 1960s at Cocoa research Institute of Nigeria CRIN consisted of, apart from efforts at chemical control, an intensive search for genotypes resisting and/or escaping the disease in the field. From among 152 clones carefully observed for natural infection for 3-6 years, 19 were identified as possibly resistant. Clones were shown to differ in seasonal pod production periodicity, and several escaped the epidemic altogether. Two screening methods were developed. The 'cotton-pad' method uses 3-5 months old unblemished pods on the tree. A zoospore suspension is soaked up in 5 x 5 cm squares of cotton wool-pad which are slapped on to the pod surface and left for 48 hours. With four fruits tested per genotype, the method gave results reflecting those of natural incidence studies, the resistance reaction taking the form of multiple pin-head infections. The 'root infection' method consisted of immersing the washed out roots of two months old seedlings in a zoospore suspension and re-potting the plants in washed river sand resulting in grossly retarded growth. The method was no tested for the relation of its results with those of the field studies as above. However, the discovery that Ppr infected feeder root tips make the floor of a plantation alive with Ppr propagules in the rainy season, indicated a more direct application of the method, i.e. breed for root resistance in order to frustrate the epidemic from the outset. Durable varieties should combine good agronomic and bean qualities, available levels of root and pod resistance and escape with a high pod value so that the beans are contained in relatively few pods. In this way, the amount of resistant substrate (the pods) available to the pathogen during the epidemic is very reduced, lowering level of natural incidence that may be further reduced by sound and frequent harvesting procedures.
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| Format: | biblioteca |
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Reading (RU) INGENIC
1999
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| Subjects: | THEOBROMA CACAO, PHYTOPHTHORA PALMIVORA, RESISTENCIA A LA ENFERMEDAD, ENFERMEDADES FUNGOSAS, FITOMEJORAMIENTO, CLONES, SEMILLAS, TAMAÑO DE LA MAZORCA, NIGERIA, |
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| Summary: | The research effort towards economic control of Phytophthora pod rot (Ppr) disease carried out in the 1960s at Cocoa research Institute of Nigeria CRIN consisted of, apart from efforts at chemical control, an intensive search for genotypes resisting and/or escaping the disease in the field. From among 152 clones carefully observed for natural infection for 3-6 years, 19 were identified as possibly resistant. Clones were shown to differ in seasonal pod production periodicity, and several escaped the epidemic altogether. Two screening methods were developed. The 'cotton-pad' method uses 3-5 months old unblemished pods on the tree. A zoospore suspension is soaked up in 5 x 5 cm squares of cotton wool-pad which are slapped on to the pod surface and left for 48 hours. With four fruits tested per genotype, the method gave results reflecting those of natural incidence studies, the resistance reaction taking the form of multiple pin-head infections. The 'root infection' method consisted of immersing the washed out roots of two months old seedlings in a zoospore suspension and re-potting the plants in washed river sand resulting in grossly retarded growth. The method was no tested for the relation of its results with those of the field studies as above. However, the discovery that Ppr infected feeder root tips make the floor of a plantation alive with Ppr propagules in the rainy season, indicated a more direct application of the method, i.e. breed for root resistance in order to frustrate the epidemic from the outset. Durable varieties should combine good agronomic and bean qualities, available levels of root and pod resistance and escape with a high pod value so that the beans are contained in relatively few pods. In this way, the amount of resistant substrate (the pods) available to the pathogen during the epidemic is very reduced, lowering level of natural incidence that may be further reduced by sound and frequent harvesting procedures. |
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