6. Variation for incomplete resistance to Hemileia vastatrix in Coffea arabica :
Disease level in the field was scored on a 0 to 9 scale. Components of resistance observed in laboratory and greenhouse tests were latency period (LP), lesion density (LD) and leaf retention period (LRP). Lines of Mundo Novo and Catuai showed relatively small but significant differences for disease level in the field. Heritability was low (0.31) and part of the variance (34) was explained by a significant correlation between disease level and yield of the lines. Among accessions from Ethiopia great variation was observed for disease level in the field. A significant part of the variance (35) was explained by differences in yield. Variation for resistance components was observed between accessions tested in the greenhouse and laboratory. However, results of the two tests were inconsistent. Transgressive segregation for incomplete resistance was observed in F2 populations of a cross between Agaro C1164-19 and Catuai, tested in the laboratory and greenhouse. Resistance was expressed by a longer LP, a lower LD, a certain percentage of nonsporulating lesions and, in some populations, early necrosis of lesions. Prospects for breeding for incomplete resistance are discussed. Factors which may hamper selection progress are: (a) the positive correlation between yield and disease level in the field, (b) the relatively small genetic variation for incomplete resistance among cultivars and productive breeding lines and (c) inconsistency of results between resistance tests
| Main Authors: | , |
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| Format: | biblioteca |
| Language: | eng |
| Published: |
1983
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| Subjects: | COFFEA ARABICA, HEMILEIA VASTATRIX, ROYA, ENFERMEDADES FUNGOSAS, RESISTENCIA A LA ENFERMEDAD, HEREDABILIDAD, RENDIMIENTO, |
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| Summary: | Disease level in the field was scored on a 0 to 9 scale. Components of resistance observed in laboratory and greenhouse tests were latency period (LP), lesion density (LD) and leaf retention period (LRP). Lines of Mundo Novo and Catuai showed relatively small but significant differences for disease level in the field. Heritability was low (0.31) and part of the variance (34) was explained by a significant correlation between disease level and yield of the lines. Among accessions from Ethiopia great variation was observed for disease level in the field. A significant part of the variance (35) was explained by differences in yield. Variation for resistance components was observed between accessions tested in the greenhouse and laboratory. However, results of the two tests were inconsistent. Transgressive segregation for incomplete resistance was observed in F2 populations of a cross between Agaro C1164-19 and Catuai, tested in the laboratory and greenhouse. Resistance was expressed by a longer LP, a lower LD, a certain percentage of nonsporulating lesions and, in some populations, early necrosis of lesions. Prospects for breeding for incomplete resistance are discussed. Factors which may hamper selection progress are: (a) the positive correlation between yield and disease level in the field, (b) the relatively small genetic variation for incomplete resistance among cultivars and productive breeding lines and (c) inconsistency of results between resistance tests |
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