Horizontal resistance in three Coffea arabica cultivars to Hemileia vastatrix :
The leaves of vertical and horizontal resistance to coffee rust were assessed in three Coffea arabica L. cultivars (Harar, Mundo Novo and Catuaí) under natural epidemic conditions. Disease assessment was effect monthly during two consecutive years, in three locations. Of the three methods available for assessing the disease (percent of infected leaves, lesions per leaf, and lesions per infected leaf), and the six transformations employed (logarithmic, logistic, monomolecular, Gompertz and Bertalanffy for n = 2 and n = 3), based on the coefficient of determination (R{ostrok}), the lesions per infected leaf parameter and the logistic transformation were proved to be the most adequate for the ascendant phase of the disease progress, while the percent of infected leaves parameter and the transformation of Bertalanffy (n = 2) were chosen for the descendant phase. Cultivars Mundo Novo and Catuaí presented values of xo (initial disease) and of r (apparent infection rate) significantly lower than those presented by cultivar Harar. The lower values of xo were due to the capacity that Mundo Novo and Catuai cultivars have of shedding infected leaves. Since this characteristic is not race-specific, this resistance mechanism constitutes un unusual type of horizontal mechanism characterized by a delay in the beginning of the disease whithin the plant population. The lower values of r were due to classic mechanisms of horizontal resistance. Of the three factors that influence the decrease of a disease under natural epidemic conditions, the data obtained in this research lead to the conclusion that the two main processes involved are dwindling inoculum, which usually starts in May, due to host conditions and unfavorable environment for the pathogen, and shedding of diseased leaves, which usually starts in July. On the other hand, dillution, which is the third factor that influences the decrease in level of disease does not play an outstanding role in the C. arabica-H. vastatrix
| Main Authors: | , , , |
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| Format: | biblioteca |
| Language: | eng |
| Published: |
1990
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| Subjects: | COFFEA ARABICA, VARIEDADES, HARRAR, MUNDO NOVO, CATUAI, HEMILEIA VASTATRIX, ROYA, ENFERMEDADES FUNGOSAS, RESISTENCIA A LA ENFERMEDAD, RESISTENCIA HORIZONTAL, BRASIL, |
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