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Avalia??o de cultivares de mandioca, para consumo in natura, quanto à resistência à mancha parda da folha

DOI: 10.1590/S0102-05362004000200014

Keywords: cercosporidium henningsii, manihot esculenta, resistance, epidemiology.

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Abstract:

two field experiments were conducted to confirm the etiological agent of the cassava 'brown leaf spot', to study the progress of the disease and to evaluate resistance, agronomic and nutritional traits of different cassava cultivars. the experiments were performed in rio de janeiro state, brazil. in the first experiment, six cassava cultivars (amarelinha, marcos op, iac-264, baiana, mantiqueira and sonora), were evaluated from february/1997 to june/1998. in the second experiment, performed from january to august/1999, the same cultivars, plus 'saracura', and 'rosada de sc' were evaluated, in a randomized complete block design, with three replicates. the intensity of the disease, initiated from natural infection, was quantified at seven and 15 days, when the severity and the incidence of injured leaves were considered. at harvest, the severity and incidence of injured leaves, defoliation rates and number of injured leaves were estimated. disease progress curves were built for the incidence and for severity data; the area under the curves was used to calculate the disease severity and infected leaf severity. there were differences among the cultivars in relation to brown leaf spot resistance, caused by cercosporidium henningsii. cultivar 'amarelinha' was the most susceptible, and 'baiana' and 'sonora' the most resistant. there were no differences between the cultivars in yield and root characteristics, except 'amarelinha' with higher root weight. there was a negative and significant correlation between the severity of the disease (expressed by the values of the area under the disease progress curve) and the number and weight of roots.

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