Investigations on a disease of Coffea arabica caused by a form of Colletotrichum coffeanum Noack, 1: Some factors affecting by the pathogen
The berry disease of Coffea arabica, caused by a form of Colletotrichum coffeanum Noack, may have arisen by mutation of the fungus from a mildly parasitic to a virulent form at some time prior to 1922. Conidia from different sources were found to vary in viability and infectivity, those from lessions on ripe berries being superior to those from green, and conidia from pure cultures on potato-dextrose agar being the least satisfactory. Different stages of the crop varied markedly in susceptibility, flowers, very young fruit, and ripe berries being the most susceptible; germination rates of conidia on the surface of flowers were comparable with those on nutrient agar. All parts of the plant can be attacked, and the fungus, which habitually colonizes the maturing bark external to the developing phellogens, can cause a disease of twigs (Elgon die-back) under abnormal conditions. There is a difference in varietal reaction to attack, berries of the Harar variety and its derivatives being the most susceptible known, and Blue Mountain the most resistant. Wounding increased susceptibility in all varieties; addition to the infection drop of extracts from berries of several different varieties increased susceptibility, with Blue Mountain having the greatest stimulatory effect and Harar none. Varietal reaction of a berry to infection cannot, however, be correlated either with the amount of germination on its surface, or with stomatal numbers, but increased germination does increase the invasion rate in dividual flowers or berries. Variation between varieties in susceptibility is ascribed to some chemical or physical difference in the cuticle, making penetration relatively more difficult in the resistant variety. At the optimum temperature of around 22ð C., and at a suitable humidity, infection can take place in as little as 2 hr
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| Format: | biblioteca |
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| Subjects: | COFFEA ARABICA, COLLETOTRICHUM, MARCHITEZ DESCENDENTE, ENFERMEDADES FUNGOSAS, EPIDEMIOLOGIA, COLLETOTRICHUM COFFEANUM, PATOGENICIDAD, |
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